Litter type affects the activity of aerobic decomposers in a boreal ...

Biogeosciences 8 2741ndash2755 2011wwwbiogeosciencesnet827412011doi105194bg-8-2741-2011copy Author(s) 2011 CC Attribution 30 License

Biogeosciences

Litter type affects the activity of aerobic decomposers in a borealpeatland more than site nutrient and water table regimes

P Strakova12 R M Niemi3 C Freeman4 K Peltoniemi2 H Toberman45 I Heiskanen3 H Fritze2 and R Laiho1

1Peatland Ecology Group Department of Forest Sciences Univ of Helsinki PO Box 27 00014 Helsinki Finland2Finnish Forest Research Institute Vantaa Research Unit PO Box 18 01301 Vantaa Finland3Finnish Environment Institute PO Box 140 00251 Helsinki Finland4Wolfson Carbon Capture Laboratory School of Biol Sciences University of Wales Deiniol Road LL57 2DG Bangor UK5Environmental Futures Centre Griffith School of Environment Griffith University Nathan Qld 4111 Australia

Received 6 December 2010 ndash Published in Biogeosciences Discuss 28 February 2011Revised 7 September 2011 ndash Accepted 11 September 2011 ndash Published 27 September 2011

Abstract Peatlands are carbon (C) storage ecosystems sus-tained by a high water table (WT) High WT creates anoxicconditions that suppress the activity of aerobic decomposersand provide conditions for peat accumulation Peatland func-tion can be dramatically affected by WT drawdown causedby climate andor land-use change Aerobic decomposersare directly affected by WT drawdown through environmen-tal factors such as increased oxygenation and nutrient avail-ability Additionally they are indirectly affected via changesin plant community composition and litter quality We stud-ied the relative importance of direct and indirect effects ofWT drawdown on aerobic decomposer activity in plant lit-ter at two stages of decomposition (incubated in the fieldfor 1 or 2 years) We did this by profiling 11 extracellularenzymes involved in the mineralization of organic C nitro-gen (N) phosphorus (P) and sulphur Our study sites repre-sented a three-stage chronosequence from pristine to short-term (years) and long-term (decades) WT drawdown condi-tions under two nutrient regimes (bog and fen) The littertypes included reflected the prevalent vegetationSphagnummosses graminoids shrubs and trees

Litter type was the main factor shaping microbial activitypatterns and explained about 30 of the variation in enzymeactivities and activity allocation Overall enzyme activitieswere higher in vascular plant litters compared toSphagnumlitters and the allocation of enzyme activities towards C ornutrient acquisition was related to the initial litter quality

Correspondence toP Strakova(petrastrakovahelsinkifi)

(chemical composition) Direct effects of WT regime sitenutrient regime and litter decomposition stage (length of in-cubation period) summed to only about 40 of the littertype effect WT regime alone explained about 5 of thevariation in enzyme activities and activity allocation Gener-ally enzyme activity increased following the long-term WTdrawdown and the activity allocation turned from P and Nacquisition towards C acquisition This caused an increasein the rate of litter decomposition The effects of the short-term WT drawdown were minor compared to those of thelong-term WT drawdown eg the increase in the activity ofC-acquiring enzymes was up to 120 (bog) or 320 (fen)higher after the long-term WT drawdown compared to theshort-term WT drawdown In general the patterns of mi-crobial activity as well as their responses to WT drawdowndepended on peatland type eg the shift in activity allo-cation to C-acquisition was up to 100 stronger at the fencompared to the bog

Our results imply that changes in plant community compo-sition in response to persistent WT drawdown will stronglyaffect the C dynamics of peatlands The predictions of de-composer activity under changing climate andor land-usethus cannot be based on the direct effects of the changedenvironment only but need to consider the indirect effectsof environmental changes the changes in plant communitycomposition their dependence on peatland type and theirtime scale

Published by Copernicus Publications on behalf of the European Geosciences Union

2742 P Strakova et al Litter type affects the activity of aerobic decomposers

1 Introduction

Peatlands are a significant atmospheric carbon (C) sink dueto a long-term imbalance between litter production and de-composition This imbalance is caused by high water tables(WT) and consequent anoxia that slows down decomposition(eg Gorham 1991 Schulze and Freibauer 2005) Globalclimate change is predicted to result in lowered WT in north-ern peatlands (Gorham 1991 Roulet et al 1992 Gitay etal 2001) via changes in precipitation patterns andor in-creased temperature and evapotranspiration Another impor-tant issue is currently the C balance of peatlands drained forforestry by ditching which is the most extensively appliedland-use practise on peatlands of Nordic countries and Rus-sia (Minkkinen et al 2008) Because peatlands representa large portion of the terrestrial C pool it is important tounderstand their role in the global C cycle and predict theirresponse to climate andor land-use change (Limpens et al2008)

Persistent lowering of the WT promotes several changesin peatland environmental conditions (Laiho 2006) that mayhave direct effects on decomposition Decreased water con-tent in the surface peat and increased soil aeration maystimulate the activity of aerobic decomposers Increasedpeat compaction may in turn slow down their activityDirect effects of WT drawdown on the current vegetationcover include changes in nutrient concentrations because ofchanges in nutrient availability or root functioning Howeverany direct effects may be overruled by the indirect effectsthrough changes in plant community structure (Dorrepaal etal 2005) These effects have not yet been thoroughly evalu-ated

A persistent change in the WT affects plant communitystructure (Weltzin et al 2000 2003 Robroek et al 2007Breeuwer et al 2009) and eventually can lead to a completeturnover of species adapted to the new conditions (Laineet al 1995a) Such changes tend to be more pronouncedin nutrient-rich sites and intensify over time (Laine et al1995a) In consequence the quantity and quality of plantlitter produced after the long-term WT drawdown greatly dif-fer from that produced under pristine conditions (Laiho et al2003 Strakova et al 2010) Such changes may have impor-tant consequences for soil C dynamics (eg Hobbie 1996Dorrepaal et al 2005 Cornelissen et al 2007 Suding et al2008)

The structure of the peatland microbial community varieswith the plant community (Borga et al 1994 Fisk et al2003 Thormann et al 2004 Jaatinen et al 2007 2008)and it has been shown that changes in peatland hydrologyaffect both (Jaatinen et al 2007 Peltoniemi et al 2009)Microbial responses in the form of enzyme activities havebeen detected (Fenner et al 2005a Toberman et al 2010)and may be directly induced by the increased availabilityof oxygen andor changes in pH The presence of bimolec-ular oxygen activates phenol oxidase enzymes that degrade

highly recalcitrant polyphenolic compounds Phenol oxidasemay also activate extracellular hydrolase enzymes by theirrelease from phenolic inhibition the ldquoenzymic latch theoryrdquo(Freeman et al 2001 2004) Decomposition is a summativeeffect of several enzymes produced by the microbial commu-nity and changes in the quality and quantity of litter inputsmay affect the activity of each enzyme in a unique manner(Hernandez and Hobbie 2010)

Indirect effects of WT drawdown on the composition andactivity of aerobic microbial decomposers in peatlands viachanges in plant community structure are in spite of theirsignificance still poorly understood (Laiho 2006 Thor-mann 2006) Furthermore soil nutrient availability may in-fluence community-level decomposition processes (Hobbieand Gough 2004) Plant communities and consequently lit-ter qualities vary along with environmental factors such asWT soil pH and nutrient availability that can affect differentspecies in different ways (Hobbie and Gough 2004) Con-sequently it is difficult to predict changes in decompositionrates in situations where the plant community andor soil fac-tors are changing As a first step we focus on the relative im-portance of substrate quality soil conditions and microbialcommunity composition on microbial activity

The aim of our study was thus to disentangle (1) direct and(2) indirect effects of WT drawdown on the activity of aer-obic microbial decomposers in boreal peatland ecosystemsand to link the activity to microbial community compositionlitter quality and litter decomposition rates We characterizedmicrobial activity by quantifying 11 extracellular enzymesinvolved in mineralization of organic C nitrogen (N) phos-phorus (P) and sulphur (S) in selected litter types typical ofour sites at two stages of decomposition By this we aimedto capture both spatial (litter type) and temporal (decompo-sition stage) variation in microbial activity The selection ofC- N- and P-acquiring enzymes was based on previous stud-ies aiming to include enzymes that play principal roles in theprocess of organic matter decomposition (eg Sinsabaugh1994 Allison and Vitousek 2004 Vepsalainen et al 2004Fenner et al 2005b Rejmankova and Sirova 2007) Addi-tionally we included the S-acquiring enzyme arylsulphatasean important enzyme of wetland soils (Kang and Freeman1999 Rejmankova and Sirova 2007)

We hypothesized that WT drawdown has (1) direct pos-itive effects on microbial enzyme activities caused by im-proved environmental conditions for aerobic decomposersand (2) indirect effects via changes in plant communitystructure and thus litter quality as the substrate for decom-posers Following WT drawdown direct effects will be ob-served as an increase in microbial enzyme activity in lit-ter types common to all WT regimes Indirect effects willbe observed as variation in enzyme activity allocation (stan-dardized activities of each enzyme within a sample) betweenthe different litter types reflecting the changes in the plantcommunities Furthermore we hypothesized that (3) therelatively nutrient-rich fen will have a higher production of

Biogeosciences 8 2741ndash2755 2011 wwwbiogeosciencesnet827412011

P Strakova et al Litter type affects the activity of aerobic decomposers 2743

C-acquiring enzymes and consequently a faster decomposi-tion rate compared to the nutrient-poor bog

WT in a peatland usually fluctuates within a certain rangedepending on season and weather conditions Such fluc-tuations have their specific effects on biogeochemical pro-cesses (Corstanje and Reddy 2004) and these may differfrom those of a persistent change (Hughes et al 1999) Inthis study we focus on a persistent change in average WTOur results may thus not be applied on temporal WT fluctu-ations or short-term droughts

2 Material and methods

21 Study sites

The research was carried out at Lakkasuo a raised bog com-plex in Central Finland (6148prime N 2419prime E ca 150 m asl)Annual rainfall in this area is 710 mm of which about one-third falls as snow The average annual temperature sum(threshold value 5C) is 1160 degree days and average tem-peratures for January and July are ndash89 and 153C respec-tively (Finnish Meteorological Institute Juupajoki weatherstation 1961ndash1990)

We had two study sites with differing nutrient regimesombrotrophic bog (precipitation-fed nutrient-poor) andmesotrophic fen (additionally groundwater-fed morenutrient-rich) Both sites included a pristine control plot aplot with short-term (ca 4 years) and a plot with long-term(ca 40 years) WT drawdown (Laine et al 2004) Togetherthese plots formed a gradient from a wet pristine peatlandthrough a drying environment and finally towards a peatlandforest ecosystem (Laiho et al 2003) Within each site allplots supported the same plant community and had similarsoil composition and structure before the WT drawdownThe pristine and long-term drained plots were about 900 m2

and the short-term drained plots about 500 m2Water tables in the experimental plots were manipu-

lated by ditching The long-term WT drawdown had beenachieved with practical-scale drainage for forestry in 1961and the short-term WT drawdown with new ditches for ourexperimental purposes in 2001 The short-term WT draw-down had led to the average WT being 10 (bog) to 20 (fen)cm deeper than in the corresponding pristine plots whichis close to the estimate given by Roulet et al (1992) for theshort-term impact of climate change on WT in northern peat-lands In the long-term drained plots the average WT was15 (bog) to 40 (fen) cm deeper than in the pristine plotsWe assumed that the initial post-drainage drop in WT wasclose to that observed in our short-term drained plots andthat further lowering was due to increased evapotranspira-tion caused by local tree stands (Sarkkola et al 2010) Thedifference between fen and bog also largely derives from thehigher tree stand evapotranspiration in fens where the treestands develop faster (Minkkinen et al 2001) As the WT

Table 1 Experimental layout litter types included in this study andthe number of replicate litterbags per litter type plot (water tableregime) and site (nutrient regime fen and bog) prepared for annualrecovery Litter ofBetula nanaandPinus sylvestriswas present atall sites and plots (common litter) while the other litter types weretypical of certain sites or plots (specific litter) The samples repre-sent a subset of an ongoing long-term decomposition study

Fen Bog

Litter type pristine STD LTD pristine STD LTD

Carex lasiocarpaleaves 2 2Betula nanaleaves 3 3 3 3 3 3Pinus sylvestrisneedles 2 2 2 2 2 2Sphagnum fallax 3 3Sphagnum angustifolium 3 3Sphagnum balticum 3 3Sphagnum fuscum 2 2 2

Plots pristine undrained STD short-term water table drawdownLTD long-term water table drawdown

depth is clearly different (usually lower) next to a drainageditch than is the average of the drained area (Grieve et al1995 Schlotzhauer and Price 1999) no measurements weremade next to the ditches (minimum distancegt1 m for theshort-term WT drawdown and 10 m for the long-term WTdrawdown)

The short-term four-year WT drawdown had a minor ef-fect on plant community composition In the long-term 40years the changes in plant community composition were dra-matic WT drawdown transformed an open peatland domi-nated bySphagnumand graminoids into a forest ecosystemdominated by pine and birch (Strakova et al 2010) In addi-tion to a lower WT the change in flora was associated with adrop in pH and increase in nutrient (N and P) concentrationsof surface peat (Strakova et al 2010)

22 The litter material

We collected 7 litter types that reflected the dominant speciesgrowing under the different nutrient and WT regimes (sitesand plots) and were of different plant groups with distinc-tive chemical composition (Strakova et al 2010) NamelyCarex lasiocarpaleaf litter Betula nanaleaf litter Pinussylvestrisneedle litter and moss litter ofSphagnum angus-tifolium Sphagnum balticum Sphagnum fallaxandSphag-num fuscum Litter of B nanaandP sylvestriswas presentin all nutrient and WT regimes (ldquocommon litterrdquo) and couldbe used to evaluate the direct effect of WT drawdown on mi-crobial activity Other litter types in our study were typical ofcertain nutrient and WT regimes (ldquospecific litterrdquo) (Table 1)and thus reflected indirect effects

Vascular plant litter was collected by harvesting senescentleaves and needles from living plants moss litter by cut-ting a 3ndash5 cm thick layer below the living moss with scissors(thus excluding both the upper green and the lower already

wwwbiogeosciencesnet827412011 Biogeosciences 8 2741ndash2755 2011


decomposing layers) Litter samples were examined and anygreen or clearly decomposing material was removed Har-vesting took place in September and October 2004 during pe-riods of highest natural litter fall at our sites (Anttila 2008)Each litter type was air-dried at room temperature (20C) toconstant mass (about 92ndash94 dry mass) and gently mixedTwo sub-samples per litter type and plot were withdrawn todetermine initial litter quality (Strakova et al 2010) Drymass content was determined by drying two sub-samples at105C overnight

Of the litter types testedB nanaleaf litter generally hadthe highest concentration of nutrients extractives (substancesextractable by hot water) and Klason lignin and the low-est concentration of holocellulose The opposite pattern wasfound for Sphagnummoss litter except for the concentra-tion of P that was also high inSphagnum Detailed chemicalcharacterization of the different litter types was presented byStrakova et al (2010)

23 Decomposition measurements

Litter decomposition was studied using the litterbag methodwhich in spite of some known sources of inaccuracy (Tay-lor 1998 Domisch et al 2000 Kurz-Besson et al 2005) isthe most practical and widely used method for determiningmass loss rates of different materials in situ To minimize thenegative effect of air-drying on litter decomposition (Taylor1998) litterbags were remoistened with surface water fromthe test plot before installation We assumed that this helpedthe microbial communities typical of the plots to re-colonizethe litter Nylon bags had a mesh size of 1times 1 mm and con-tained on average 5 g and 4 g of air-dried litter for vascularplants and moss respectively For each plot (nutrient andWT regime) 2ndash3 replicates per litter type were prepared forannual recovery (Table 1)

Litterbags with vascular plant litter were placed horizon-tally on the surface where litters naturally fall always in con-tact with fallen litter of the same type Litterbags contain-ing moss litter were installed under the living parts of mossshoots of the given species where moss litter is naturallyformed and begins to decompose Installation took place inOctoberndashNovember 2004 Incubation periods presented hereare years 1 and 2 and represent a subset of an ongoing long-term study

After each recovery litterbags were transported to the lab-oratory where their contents were cleaned by removing alladditional (ingrowth) materials weighed to determine the re-maining ldquofreshrdquo mass and gently homogenized before sub-sampling Two sub-samples were taken from each litterbagfor the enzyme assays one for the microbial communitycomposition analysis and two for dry mass content determi-nation Dry mass content of the ldquofreshrdquo samples was deter-mined by drying two sub-samples at 105C overnight De-composition rates were expressed as dry mass loss after eachincubation period (Appendix A)

24 Enzyme assays

Measurements of extracellular enzyme activities in soil arevery sensitive to sample handling and storage Further theyare strongly affected by the pH of the reaction mixture andthe incubation temperature In earlier studies both ldquolabora-toryrdquo (pH-buffered reaction mixture incubation temperaturehigher than in the field) and ldquonaturalrdquo conditions have beenapplied (eg Kang and Freeman 1999 Vepsalainen et al2001 Sinsabaugh et al 2002 Fenner et al 2005b Niemiand Vepsalainen 2005 Romanı et al 2006) The first ap-proach gives information about the potential enzyme activi-ties and especially the quantity of active enzymes (Kang andFreeman 1999) The second approach more closely reflectsthe actual natural processes including the influence of possi-ble litter type or environmentally-related differences in pHas well as the influence of site temperature that might berather low in some environments Outcomes may vary be-tween the two approaches (Freeman et al 1995)

We measured enzyme activities using both approachesHenceforth we refer to the outcomes potential activities (PA)and actual activities (AA) for those assayed in buffered con-ditions with incubation temperature 20C and non-bufferedconditions with incubation temperature 5C respectivelyAssays were performed in separate laboratories both havingextensive experience with the given approach (eg Freemanet al 2001 Vepsalainen et al 2001)

241 Potential activities (PA)

PA were assayed according to Vepsalainen et al (2004) us-ing the ZymProfilerreg test kit Substrates used for the as-says are listed in Table 2 The substrate and standard so-lutions were freeze-dried on multiwell plates and stored atndash20C until assayed Prior to the measurements 20 microl ofdimethyl sulfoxide was added to the wells used for chitinaseand phosphomonoesterase activity measurements to improvesubstrate dissolution

Based on the pH values of the litters (Appendix A) andpeat soil (Table 1 in Strakova et al 2010) at our sites weused site-specific buffer to control pH 05 M sodium acetatebuffer at pH 55 for samples from the fen pristine and short-term drained plot and Modified Universal Buffer (MUB)(Tabatabai 1994) at pH 4 for samples from the fen long-termdrained plot and all three bog plots To examine the effectof the buffer pH on enzyme activities samples from the fenlong-term drained plot were assayed using both buffers

Litter samples were stored at ndash20C and assayed 6 monthsafter the litterbag recovery An aliquot of 10 g or 50 g of thefrozen foliar or moss litter respectively was homogenisedin 35 ml of buffer using an OmniMixer (Omni InternationalUSA) for 3 min at 9600 rev minminus1 in an ice bath The ho-mogenates were further diluted by the buffer to a final dilu-tion of 1100 and 5100 for the foliar and moss litter respec-tively and 200 microl aliquots of the homogenates were added



Table 2 Fluorogenic substrates used for the enzyme activity measurements

Enzyme Assay Substrate Element Macromolecule degraded

Arylsulphatase PA MUF-sulphate S Organic sulphurα -Glucosidase PA MUF-α-D-glucopyranoside C Starch and glycogen

β-GlucosidaseAA MUF-β-D-glucoside

C CellulosePA MUF-β-D-glucopyranosideβ-Xylosidase PA MUF-β-D-xylopyranoside C Xylane xylobioseCellobiosidase PA MUF-β-cellobiopyranoside C CelluloseChitinase AA PA MUF-N-acetyl-β-D-glucosaminide C N Chitin chitobiosePhenol oxidase AA L-DOPA C Phenolic compoundsPhosphomonoesterase AA PA MUF-phosphate P Hydrolysis of phosphate estersPhosphodiesterase PA bis-MUF-phosphate P Hydrolysis of phosphate diestersAlanine-aminopeptidase PA L-alanine-AMC N Oligopeptidesrarr amino acidsLeucine-aminopeptidase PA L-leucine-AMC N Oligopeptidesrarr amino acids

Assays AA actual activities PA potential activities (see text for details) Substrates AMC 7-amido-4-methylcoumarin DOPA dihydroxyphenylalanine MUF 4-methylumbelliferone

directly to the freeze-dried substrates to yield substrate con-centrations of 500 microM Similarly 200 microl aliquots of the ho-mogenate were used in the standard measurements to yieldconcentrations ranging from 05 to 100 microM for MUF (4-methylumbelliferone) substrates and from 01 to 50 microM forAMC (7-amido-4-methylcoumarin) substrates

The reference blank fluorescence of the samples was mea-sured immediately after adding the sample homogenate Flu-orescence values of the end products were obtained from themeasurements after 15 h (MUF substrates) or 3 h (AMC sub-strates) incubation on a multiwell shaker at 20C in the darkFluorescence was measured with a Wallac Victor2TM multi-label counter (EGampG Wallac Finland) using an excitationfilter of 355 nm and an emission filter of 460 nm

A mean based on four replicate blanks was subtractedfrom corresponding enzyme activity measurements and theMUF and the AMC concentrations were calculated usingstandard curves Results from three replicate reaction wellswere averaged for each enzyme and litterbag and the enzymeactivity was expressed as micromol of substrate converted perminute and per g of litter dry mass

242 Actual activities (AA)

AA of β-glucosidase chitinase and phosphomonoesterasewere assayed according to Gusewell and Freeman (2005) us-ing MUF substrates (Table 2) Litter samples were stored at4C and assayed within 2 weeks of litterbag recovery Lit-ter was coarsely chopped with scissors and 1 cm3 of foliaror 2 cm3 of moss litter was mixed with 6 or 7 ml ultra-purewater respectively using a Stomacher machine (Seward Col-worth model 400 London UK) to minimize cell disruptionFor each of the hydrolases assayed a 05 ml aliquot of theextract (without large litter pieces) was transferred to an Ep-pendorf reaction vial and 025 ml of the appropriate substratesolution (Table 2) was added Substrates were pre-dissolved

in cellosolve (2-ethoxyethanol) as they have minimal solubil-ity in pure water The concentration of the substrate solutionwas 400 microM for the activity ofβ-glucosidase and chitinaseand 200 microM for the activity of phosphomonoesterase

Samples were mixed and incubated at field temperature(5C) for 45 min (phosphomonoesterase) or 60 min (β-glucosidase and chitinase) Reactions were terminated bycentrifugation at 10 000 rpm for 5 min and the fluorescence ofthe supernatant was measured immediately on a microplatereader (Perkin-Elmer) at 460 nm emission and 355 nm ex-citation wavelength For each assay a range of standardconcentrations of MUF in cellosolve was made up in litterextract obtained and incubated under identical conditions asthose described above except for the substrates Thus cal-ibration curves accounted for possible interactions betweenMUF and other compounds in the litter extracts Enzymeactivities were expressed as micromol of substrate converted perminute and per g of litter dry mass Results from two repli-cate assays were averaged for each litterbag

Extracellular phenol oxidase activity was determined ac-cording to Fenner et al (2005a) using 10 mmL-DOPA (di-hydroxyphenylalanine) solution as substrate A suspensionof 1 cm3 litter and 9 ml of ultra-pure water was prepared inthe same way as for the hydrolases and 300 microl aliquots of theextract were transferred into two 15 ml Eppendorf reactionvials Extracts were diluted with 450 microl of ultra-pure waterand 750 microl of either 10 mmL-DOPA solution or ultra purewater (control) was added to each vial The samples weremixed and incubated at field temperature (5C) for 9 min(mixed once at 45 min) The reaction was terminated by cen-trifugation at 10 000 rpm for 5 min From each reaction vial300 microl aliquots of the supernatant were immediately pipet-ted into three wells of a clear microplate and absorbance wasmeasured at 460 nm Mean absorbance of the three controlwells was subtracted from that of the threeL-DOPA wells



and phenol oxidase activity was calculated using the Beer-Lambert law

c = Aεl (1)

wherec = concentration of theL-DOPA product (M)A = av-erage absorbance calculated as described aboveε = molarabsorbency coefficient for theL-DOPA product (37times 104)l = path length (cm)

Phenol oxidase activity was expressed as micromol ofthe L-DOPA product (23-dihydroindole-56-quinone-2-carboxylate diqc) produced per minute and per g of litterdry mass Results from three replicate assays were averagedfor each litterbag All solutions required for the assays weremaintained at field temperature (5C)

25 Microbial community analyses

In oxic conditions aerobic bacteria and fungi are the mostimportant and effective decomposers of organic matter inpeatlands (Peltoniemi 2010 and references therein) To pro-file the active microbial community analyses were based onribosomal RNA extracted directly from the litter samplesRNA is more short-lived compared to DNA and is a bet-ter index of the microorganisms that were active at the timeof sampling Total RNA was extracted from deep-frozen (ndash80C) litters following Korkama-Rajala et al (2008) withminor modifications Reverse transcription of rRNA into itscomplementary DNA (cDNA) was conducted as in Pennanenet al (2004) with primer FR1 (Vainio and Hantula 2000) andwith universal bacterial primer R1378 (Nubel et al 1996)PCR from diluted cDNA template was conducted with fun-gal 18S rRNA primers and with actinobacterial 16S rRNAprimers The amplified cDNA products were analyzed bydenaturing gradient gel electrophoresis (DGGE) The DGGEbands were selected for sequencing excised reamplified pu-rified and sequenced The partial fungal and actinobacterialDGGE-derived sequences were aligned with sequences re-trieved from databases of GenBankEMBLDDBJ and RDP-II release 944 (Cole et al 2005) True chimeric and clearlynon-fungal or non-actinobacterial sequences were eliminatedfrom further analyses Phylogenetic analyses were con-ducted as in Jaatinen et al (2008)

We assumed that discrete bands within a profile differen-tiated by PCR-DGGE represent different taxa from a micro-bial consortium In this study the data recovered were usedto indicate the composition of litter-degrading actinobacte-ria and fungi in relation to enzyme activities The microbialdata are a subset of a more extensive study on the microbialcommunities in the same sites (Peltoniemi 2010)

26 Data analyses

261 General patterns

Ordination methods were applied due to the presence ofmultiple intercorrelated variables We chose linear response

models (redundancy analysis RDA and principal compo-nent analysis PCA) based on the heterogeneity of the re-sponse variable data ie the extent of response variableturnover This was evaluated using detrended correspon-dence analysis (DCA) (Leps andSmilauer 2003) Standard-ized values of enzyme activities were used to minimize scaleeffects The ordinations were performed using Canoco forWindows version 45 (ter Braak andSmilauer 2002) Basedon preliminary tests the AA and PA data ofβ-glucosidasechitinase and phosphomonoesterase (the enzymes assayed byboth methods) were merged for the final ordinations in orderto simplify the main patterns presented in this paper

To estimate the proportion of total variation in enzyme ac-tivities explained by litter type nutrient regime WT and litterdecomposition stage (length of incubation period) variationwas partitioned by RDA Enzyme activity values were usedas response variables and a group of binary variables describ-ing either litter type nutrient regime (site) WT regime (plot)or decomposition stage (incubation period year 1 and 2) wasused as explanatory variables while the others were used ascovariables To analyse the overall pattern (including the in-direct effects via changes in plant community structure seehypotheses) all litter types (common and specific see Ta-ble 1) were included in the analysis The significance of thecanonical axes was evaluated using a Monte Carlo permu-tation test with 499 permutations with a reduced model andcovariables as blocks for permutations

Standardized activities of each enzyme within a samplewere calculated (henceforth called ldquoenzyme activity alloca-tionrdquo) and PCA was used to explore the main gradient in ac-tivity allocation To examine possible correlation betweenpatterns of phenol oxidase and hydrolases PCA was carriedout using the hydrolase activities as response variables Cor-relations between the resulting PCA sample scores and theactivity of phenol oxidase were then measured

262 Direct effects of site nutrient and WT regime

The direct effects of WT drawdown (Hypothesis 1) site nu-trient regime (Hypothesis 3) or incubation period on enzymeactivities were analyzed by repeated measures ANOVA onthe common litter followed by Tukeyrsquos post-hoc compari-son to test significance among the WT regimes or sites atp le 005 Separate analyses were performed for each en-zyme

The effect of buffer pH on enzyme activities (estimatedfor samples from the fen long-term drained plot only) wasestimated by ANOVA with litter type and pH as groupingfactors In all cases ANOVA was performed using Statisticafor Windows version 61 (StatSoft 2003)

263 Litter type effects

The effect of litter type on enzyme activity allocation (Hy-pothesis 2) was estimated based on the variation partitioning



results obtained by RDA (described under General patterns)To explore correlations between the main gradients in en-

zyme activities and litter quality and mass loss sample scoresfrom the PCA analysis on enzyme activity allocation (de-scribed under General patterns) were plotted with differentlitter quality parameters and mass loss rates

264 Effects of microbial community composition

To explore the correlation between the patterns of enzymeactivities and microbial community composition PCA wascarried out using binary variables describing presence or ab-sence of microbial DGGE bands as response variables Theresulting PCA sample scores were then used as explanatoryvariables in RDA where enzyme activities were used as re-sponse variables Sequences showing a significant correla-tion with enzyme activities were selected by RDA with man-ual forward selection of explanatory variables Measured ac-tivities of different enzymes were used as response variablesand binary variables describing presence or absence of mi-crobial DGGE bands as explanatory variables The signifi-cance of the contribution of each explanatory variable to thefinal model was evaluated using a Monte Carlo permutationtest with 499 permutations with a reduced model atp le 005

The number of DGGE bands per sample was used as a sur-rogate for microbial diversity To estimate the correlation be-tween patterns of enzyme activities and microbial diversityRDA was carried out using activities of different enzymes asresponse variables and the number of DGGE bands per sam-ple as the explanatory variable

3 Results

31 General patterns

Litter type explained the most variation in enzyme activities(Table 3) Effects of site nutrient and WT regime and lit-ter decomposition stage (incubation period) summed to onlyabout 40 of the litter type effect

The main gradient (32 ) in enzyme activity allocationwas attributed to the acquisition of C and P (negative mutualcorrelation not shown) The second main gradient (21 )was attributed to the acquisition of N (not shown)


The enzyme activities were generally higher in vascular plantlitters compared toSphagnumlitters (Appendix A) InBnana leaf litter enzyme activities were allocated mainly toC acquisition whereas P acquisition was the main activity inSphagnumandC lasiocarpalitters (Figs 1 and 2)Sphag-num fallaxlitter was distinguished from other moss speciesby allocating enzyme activities into N and S acquisition (notshown)

Fig 1 Differences between litter types based on redundancy anal-ysis (RDA) of the enzyme activity allocation Dummy variablesindicating incubation periods and plots of different nutrient andwater table regimes were used as covariables The first and thesecond axis account for 223 and 50 of the total variationrespectively Grey arrows potential activity black arrows ac-tual activity (see Material and Methods) Enzymesα-GLU α-glucosidaseβ-GLU β-glucosidaseβ-XYL β-xylosidase ALAalanine-aminopeptidase ARY arylsulphatase CEL cellobiosidaseCHI chitinase LEU leucine-aminopeptidase PDE phosphodi-esterase PHOX phenol oxidase PME phosphomonoesterase

Allocation of enzyme activity towards C acquisition (in-creased activity of C enzymes relative to the activity of PN and S enzymes) was positively correlated with litter massloss and the initial concentration of extractives (substancesextractable by hot water) and Klason lignin (both high infoliar litter and low in Sphagnum) and negatively corre-lated with the initial concentration of holocellulose (high inSphagnumand low in foliar litter) (Fig 2) Allocation ofenzyme activity towards P acquisition (increased activity ofP enzymes relative to the activity of C N and S enzymes)was positively correlated with CP and NP ratios in vascularplant foliar litter (high inC lasiocarpa low in B nana)

33 Environmental effects

The long-term WT drawdown had a direct positive effecton the quantitative measures of C-acquiring enzymes whilethe effect of the short-term WT drawdown was minor The



Table 3 Variation partitioning using redundancy analysis (RDA) showing percentage of the total variation in enzyme activities and activityallocation explained by litter type nutrient and water table regime and litter decomposition stage (incubation period) To analyse the overallpattern rather than the direct effects (see hypotheses) all litter types (common and specific see Table 1) were included in the analysis Alleffects were significant atp lt 0002

Enzyme activities Activity allocationMain effect F -ratio Explanatory power () F -ratio Explanatory power ()

litter type123 78 255 102 311water table regime234 34 39 57 59site nutrient regime134 86 48 95 49incubation period124 40 24 39 20

Covariables used in the test1 water table regime2 nutrient regime3 incubation period4 litter type

increase in the activity of C-acquiring enzymes was 10ndash120 (bog) to 110ndash320 (fen) higher after the long-termWT drawdown compared to the short-term WT drawdown(Fig 3) Enzyme activities generally turned from N and P ac-quisition towards C acquisition following the long-term WTdrawdown (Fig 4) Site nutrient regime had a direct effecton the allocation of enzyme activities The observed patternrejected our hypothesis in that enzyme activity actually em-phasized N and P acquisition at the nutrient-rich fen morethan at the nutrient-poor bog (Fig 4) The shift in allocationof enzyme activities from N and P acquisition towards C ac-quisition was 10ndash100 stronger at the fen compared to thebog (Fig 4)


Microbial community composition explained about 20 ofthe total variation in the enzyme activities (not shown) How-ever no strong patterns emerged and the influence of micro-bial community on enzyme activity was difficult to interpretFurthermore there were no clear changes in enzyme activ-ities between the two stages of litter decomposition eventhough the incubation period accounted for some part of thetotal variation (Table 3) and the microbial community com-position changed (not shown)

4 Discussion

41 Litter type effects overruled the direct effects of WTdrawdown

As hypothesized litter type was the main factor determiningmicrobial activity in decomposing litter In reflection of litterquality (Strakova et al 2010) microbial activity of vascularplant litters generally differed from that of mosses andClasiocarpalitter was more similar to moss litters than othervascular plant litters Considering the dramatic changes inenvironment induced by WT drawdown in our study sites itis noteworthy that change in litter type (indirect effect of WT

Fig 2 Correlations between the main gradient in enzyme activityallocation and litter mass loss initial concentration of extractives(substances easily extractable by hot water) Klason lignin holo-cellulose CP and NP ratio The main gradient in enzyme activityallocation (vertical axis of the graphs) represents the first axis fromprincipal component analysis (PCA) on standardized activities ofeach enzyme within a sample This main gradient accounted for32 of the total variation in enzyme activities and was positivelyassociated with the acquisition of C (ie positively correlated withthe standardized activities of C-acquiring enzymes) and negativelyassociated with the acquisition of P (ie negatively correlated withthe standardized activities of P-acquiring enzymes)



Fig 3 Direct effects of water table (WT) drawdown and site nutri-ent regime on activities of C-acquiring enzymes Enzyme activitydata are presented as averages per litter type and plot (nutrient andWT regime) the error bars represent standard error of mean SiteWT regimes STD short-term WT drawdown LTD long-term WTdrawdown

Fig 4 Direct effects of water table (WT) drawdown and site nu-trient regime on enzyme activity allocation Data are presented asaverages per litter type and plot (nutrient and WT regime) the er-ror bars represent standard error of mean (se) For N-acquiringenzymes se was less than 05 C C-acquiring enzymes N N-acquiring enzymes P P-acquiring enzymes Site WT regimesSTD short-term WT drawdown LTD long-term WT drawdownPatterned bar fill marks the bog site

drawdown) overwhelmed the direct effects of WT drawdownon aerobic microbial activity Our results are further sup-ported by microbial community composition that revealedsimilar patterns (Peltoniemi 2010)

Because litter quality within litter types did not vary muchbetween nutrient and WT regimes (Strakova et al 2010) thedetailed characterization of litter quality did not allow us toaccount for more variation in enzyme activities than the littertype alone Still some noteworthy points are revealed whenexamining the chemical parameters P is often the limitingnutrient in boreal peatlands If P limitation of decomposersis reduced in P-rich litter decomposers seem to invest intoC-acquiring enzymes that produce high litter decompositionrates This was the case inB nanaleaf litter with initially lowCP and NP ratio and high concentration of easily assimil-able compounds (extractives) but also a high concentrationof more recalcitrant compounds captured in the Klason ligninfraction (Fig 2)

Enzyme activity allocation towards nutrient acquisitionis believed to reflect microbial nutrient demand (eg Sins-abaugh 1994 Allison and Vitousek 2004) Enzyme activ-ity allocation towards P acquisition was detected inSphag-nummoss litters irrespective of their initial CP or NP ratiowhich varied among species Unlike other litter types de-composingSphagnumlitter was heavily colonized by plantroots that had penetrated the litterbags Some enzymes par-ticularly phosphatases may have been produced by roots orassociated mycorrhiza (Nannipieri et al 2002) and thus theactivities of P-acquiring enzymes we detected inSphagnumlitter may in part be confounded by these external sources

We found no clear relationship between the activity of phe-nol oxidase and the hydrolases in the decomposing litter un-like in earlier studies where phenol oxidase released extra-cellular hydrolases from phenolic inhibition in oxic peat soillayers (Freeman et al 2001 2004) Our decomposing littersrepresented rather fresh material compared to peat and whenthe litters become more decomposed ie have a higher con-centration of recalcitrant compounds phenol oxidase mayplay a more important role in regulating decomposition Phe-nol oxidase activity tended to be rather high inSphagnumlit-ter that had high concentrations of hemicellulose and cellu-lose but also a relatively high content of p-hydroxy phenols(CuO oxidation phenolic products) and other componentsthat were captured in the soluble lignin and Klason ligninfractions (Strakova et al 2010) It seems that inSphagnumlitter microbes are not able to directly use C from hemicel-lulose and cellulose (Hajek et al 2011) and need to producephenol oxidase to release C from the polyphenols and otherldquolignin-like componentsrdquo Decomposition ofSphagnumwasthus slow compared to other types (Fig 2) in line with ear-lier research

42 Direct environmental effects were significant butrather small

421 Water table effect

As hypothesized WT drawdown had a direct positive ef-fect on microbial activity leading to higher activity of C-acquiring enzymes and faster decomposition rates In our ex-periment litter was generally decomposing in the oxic layerin all WT regimes Thus the aerobic decomposer communitywas not restricted by saturation even in the pristine plots un-like in peat (Fenner et al 2005a) and factors other than in-creased substrate aeration affected microbial activity follow-ing WT drawdown These might include an increase in theaeration and consequently nutrient availability of the sur-face peat as well as changes in peat and litter pH



Fig 5 Effect of pH on the enzyme activities Increase (positive val-ues) or decrease (negative values) () of the activity with decreasedpH (activity at pH 4 compared to that at pH 55) Data are pre-sented as averagesplusmn standard error of meann = 16 lowastlowastp le 0002lowastp le 005 NS nonsignificant C C-acquiring enzymes N N-acquiring enzymes P P-acquiring enzymes S S-acquiring en-zymes

Peat and litter pH became more acidic with the long-termWT drawdown at the fen site probably as a result of iso-lation from the supply of base-rich groundwater that has aneutralizing effect in pristine fens enhanced oxidation of or-ganic and inorganic compounds as well as increased inputsof organic acids and greater uptake of base ions after the es-tablishment of tree cover (Laine et al 1995b) Loweringof soil pH following the long-term WT drawdown has beenreported previously (Laine et al 1995a) and affects severalprocesses in peatlands (Laiho 2006) It is likely that the low-ered pH contributed to the increased activity of C-acquiringenzymes at the fen site following the long-term WT draw-down (Fig 5 Niemi and Vepsalainen 2005) that producedhigh litter decomposition rates

Contrary to our findings for decomposing litter suppres-sion of phenol oxidase (also a C-acquiring enzyme) activityin peat as a result of lowered peat pH following the long-termWT drawdown was detected at the same sites (Tobermann etal 2010) For both peat and litter the same patterns werealso observed at the bog although no drop in pH was detectedat this site following the long-term WT drawdown These ob-servations suggest that there are different factors regulatingmicrobial activity in peat and litter and these factors mayvary between bog and fen sites Its noteworthy that the ef-fects of WT drawdown on microbial activity were dominantin the long-term when the dramatic changes in vegetationcomposition (indirect effect of WT drawdown) overruled thedirect effects of the changed environment

422 Site effect

Contrary to our expectations an increased production ofC-acquiring enzymes and faster decomposition rate wasobserved at the nutrient-poor bog compared to the morenutrient-rich fen site One possible explanation of this find-ing is adaptation and specialization of decomposers to plantspecies characteristic of a given community a ldquohome fieldadvantagerdquo (Hunt et al 1988 Gholz et al 2000 Bragazzaet al 2007 Strickland et al 2009) Litter types included incommon litter represent plant species more typical of bogsie B nanaandP sylvestris This is logical since no typ-ical fen plants can be found in bogs Such litters may thendecompose more slowly in the fen communities that havelower abundance of comparable plant material and associatedmicrobial decomposers irrespective of a favorable environ-ment This mechanism may also be involved in the increaseof decomposition rates of common litter following WT draw-down as the species are also typical of drained plots (an indi-rect effect of WT drawdown)

Finally the site effect we detected might be influenced bypeat and litter pH as discussed above for the WT effect Theactivity response to pH varied among enzymes (Fig 5) inline with other studies (Niemi and Vepsalainen 2005 Kangand Freeman 1999) Lower pH resulted in generally higheractivities of C-acquiring enzymes in the bog and P- N- andS-acquiring enzymes in the fen

43 Vague effects of microbial community composition

Microbial community composition (presenceabsence of aDGGE band) accounted for some part of the total variationin enzyme activities However the role of microbial com-munity composition in shaping the patterns of enzyme ac-tivities was difficult to interpret Quantitative data concern-ing the microbial community would likely be more informa-tive From the sequences that showed a significant correla-tion with enzyme activities fungal sequences were related tovarious saprotrophic fungi found previously in soil and plantlitter Most of the actinobacterial sequences were related tosome unknown clones or isolates coming from various en-vironments emphasizing the need to examine this microbialgroup more closely

Succession of microbial communities as decompositionproceeds and litter quality changes (Kubartova et al 2007Peltoniemi 2010) should be reflected in enzyme activitiesHowever the effect of decomposition stage (length of incu-bation period) on enzyme activities in our litters was rela-tively trivial and of no clear pattern Stabilisation of enzymesdue to the attachment of particles (Gianfreda and Bollag1996) could partly explain this absence of variation whereone might expect it Also litter decomposition in the envi-ronment is regulated by substrate availability that cannot beincluded in laboratory assays



Table A1 Enzyme activity (micromol of substrate converted per minute and per g of litter dry weight) mass loss () and pH mean values perlitter type and plot of different nutrient andor water table regimes with standard error of mean in parenthesis The standard error indicatesvariation in enzyme activities and mass loss within a plot

AA

β-glucosidase chitinase phosphomonoesterase phenol oxidaselitter type nutrient and WT regime n yr1 yr2 yr1 yr2 yr1 yr2 yr1 yr2

CL-L fen -PR 2 179 (010) 425 (033) 277 (018) 318 (132) 1321 (103) 3026 (188) 2993 (1998) 1382 (1382)CL-L fen -STD 2 1041 (202) 626 (016) 937 (237) 417 (099) 4127 (633) 2152 (601) 0 1413 (1413)BN-L fen -PR 3 459 (256) 899 (544) 312 (192) 1573 (1282) 865 (281) 2092 (337) 2051 (814) 1728 (593)BN-L fen -STD 3 1045 (501) 1358 (369) 302 (162) 1248 (1036) 1666 (552) 1628 (464) 989 (625) 4461 (844)BN-L fen -LTD 3 967 (193) 1547 (051) 218 (032) 1018 (905) 852 (086) 1511 (327) 3389 (974) 902 (382)BN-L bog -PR 3 172 (028) 1484 (043) 128 (064) 603 (167) 585 (163) 2102 (250) 319 (319) 1461 (269)BN-L bog -STD 3 867 (265) 1460 (309) 319 (148) 1403 (560) 1452 (403) 2254 (094) 196 (196) 097 (097)BN-L bog -LTD 3 1192 (374) 1174 (232) 789 (213) 356 (041) 1625 (097) 1202 (312) 1159 (588) 248 (238)P-N fen -PR 2 265 (184) 169 (015) 328 (161) 578 (463) 2229 (391) 2418 (047) 1620 (1620) 341 (341)P-N fen -STD 2 367 (122) 1617 (013) 384 (156) 486 (389) 2188 (189) 1821 (071) 262 (262) 509 (509)P-N fen -LTD 2 371 (219) 891 (160) 405 (066) 1115 (537) 2181 (602) 1458 (091) 2634 (1201) 4600 (444)P-N bog -PR 2 163 (016) 2142 (636) 295 (036) 942 (032) 2047 (295) 1964 (137) 0 0P-N bog -STD 2 622 (348) 2661 (033) 265 (084) 1751 (072) 1651 (181) 2140 (052) 0 720 (568)P-N bog -LTD 2 614 (043) 1616 (224) 1027 (357) 2284 (1209) 1667 (256) 1948 (439) 3439 (429) 1593 (497)SFA fen -PR 3 248 (032) 394 (057) 102 (011) 269 (055) 1410 (270) 2750 (437) 2032 (2032) 2408 (795)SFA fen -STD 3 214 (034) 310 (053) 125 (017) 222 (037) 1424 (187) 3309 (649) 504 (504) 893 (224)SA fen -LTD 3 218 (058) 286 (088) 206 (015) 288 (015) 1419 (157) 2113 (243) 4287 (1466) 2205 (544)SA bog -LTD 3 252 (090) 215 (114) 297 (098) 218 (054) 3428 (907) 2235 (621) 4719 (2231) 1715 (490)SB bog -PR 3 097 (010) 125 (009) 069 (008) 086 (008) 866 (096) 1012 (096) 3008 (2116) 223 (183)SB bog -STD 3 095 (019) 138 (010) 073 (007) 108 (003) 1067 (281) 926 (109) 1990 (1522) 487 (160)SFC bog -PR 2 080 (0003) 122 (003) 080 (007) 086 (003) 579 (106) 958 (254) 022 (022) 124 (124)SFC bog -STD 2 100 (023) 193 (050) 126 (024) 154 (036) 1306 (527) 1670 (130) 820 (284) 1811 (121)SFC bog -LTD 2 208 (075) 106 (004) 488 (327) 178 (039) 3519 (1559) 1540 (197) 7789 (4879) 1055 (515)

Table A1 Continued

PA

αminusglucosidase β-glucosidase cellobiosidase β-xylosidaselitter type nutrient and WT regime n yr1 yr2 yr1 yr2 yr1 yr2 yr1 yr2

CL-L fen-PR 2 059 (006) 061 (016) 1083 (453) 650 (042) 360 (152) 254 (058) 454 (099) 345 (126)CL-L fen-STD 2 108 (043) 073 (025) 1586 (290) 1069 (056) 365 (012) 482 (169) 508 (200) 556 (148)BN-L fen -PR 3 085 (013) 117 (007) 1024 (380) 528 (158) 254 (074) 171 (012) 347 (044) 272 (037)BN-L fen -STD 3 116 (024) 133 (036) 780 (218) 895 (117) 365 (153) 263 (079) 290 (063) 394 (094)BN-L fen -LTD 3 144 (009) 194 (085) 6017 (1820) 4096 (395) 1243 (194) 1015 (212) 837 (076) 1110 (278)BN-L bog-PR 3 109 (012) 143 (029) 8741 (1280) 8596 (1582) 1667 (301) 1665 (506) 857 (023) 1201 (363)BN-L bog -STD 3 151 (019) 161 (019) 8399 (871) 7983 (3274) 2219 (246) 1305 (599) 1044 (127) 1083 (326)BN-L bog -LTD 3 149 (004) 182 (060) 9457 (436) 8398 (2454) 2029 (205) 2714 (1731) 1170 (120) 1028 (310)P-N fen -PR 2 074 (003) 075 (019) 192 (008) 192 (030) 019 (019) 087 (037) 076 (002) 067 (006)P-N fen -STD 2 086 (013) 101 (008) 542 (021) 957 (028) 100 (006) 243 (012) 161 (013) 258 (013)P-N fen -LTD 2 064 (005) 139 (008) 1800 (013) 3871 (2215) 578 (157) 766 (131) 269 (097) 569 (076)P-N bog -PR 2 073 (015) 128 (043) 1509 (321) 2686 (908) 278 (096) 552 (181) 271 (038) 325 (085)P-N bog -STD 2 072 (002) 074 (017) 1735 (239) 2450 (215) 360 (036) 585 (187) 273 (013) 303 (079)P-N bog -LTD 2 120 (007) 147 (064) 3023 (801) 4963 (1368) 729 (055) 1034 (251) 407 (026) 634 (297)SFA fen -PR 3 165 (049) 010 (005) 1231 (288) 109 (032) 450 (160) 041 (017) 693 (079) 066 (003)SFA fen -STD 3 115 (072) 013 (009) 564 (282) 128 (021) 272 (156) 032 (008) 300 (168) 063 (004)SA fen -LTD 3 005 (005) 022 (018) 1859(728) 994 (535) 400 (256) 168 (107) 394 (215) 311 (169)SA bog -LTD 3 057 (029) 004 (004) 2635 (1036) 288 (122) 500 (179) 068 (017) 594 (189) 080 (021)SB bog -PR 3 0 0 1251 (473) 024 (013) 0 0 240 (095) 017 (008)SB bog -STD 3 036 (029) 004 (002) 821 (648) 145 (016) 130 (094) 018 (004) 219 (158) 046 (001)SFC bog -PR 2 121 (081) 038 (016) 1126 (812) 170 (020) 187 (099) 048 (017) 357 (247) 097 (017)SFC bog -STD 2 156 (115) 033 (009) 840 (432) 516 (154) 124 (060) 086 (023) 223 (134) 122 (016)SFC bog -LTD 2 113 (009) 094 (024) 1134 (591) 663 (071) 254 (007) 106 (031) 377 (046) 247 (032)



Table A1 Continued

PA

chitinase leucine-aminopeptidase alanine-aminopeptidase arylsulphataselitter type nutrient and WT regime n yr1 yr2 yr1 yr2 yr1 yr2 yr1 yr2

CL-L fen -PR 2 1018 (501) 571 (311) 409 (069) 635 (079) 367 (152) 544 (188) 046 (034) 076 (067)CL-L fen -STD 2 3063 (1224) 875 (004) 427 (196) 491 (151) 685 (423) 508 (214) 003 (003) 011 (005)BN-L fen -PR 3 544 (242) 2310 (1580) 285 (023) 359 (010) 311 (029) 433 (014) 028 (017) 059 (019)BN-L fen -STD 3 1585 (859) 5459 (5033) 282 (002) 630 (334) 509 (169) 431 (154) 023 (005) 030 (014)BN-L fen -LTD 3 4897 (3558) 6471 (5789) 087 (016) 097 (031) 115 (014) 122 (030) 018 (009) 042 (033)BN-L bog -PR 3 3199 (1278) 4601 (2637) 059 (011) 086 (022) 073 (006) 110 (031) 012 (003) 026 (010)BN-L bog -STD 3 3250 (1310) 3470 (910) 062 (005) 077 (005) 064 (008) 089 (010) 018 (001) 033 (004)BN-L bog -LTD 3 4774 (522) 2004 (731) 102 (009) 098 (023) 105 (017) 119 (023) 024 (002) 020 (008)P-N fen -PR 2 299 (026) 504 (343) 075 (018) 181 (009) 096 (016) 206 (009) 006 (003) 007 (001)P-N fen -STD 2 382 (080) 675 (192) 124 (023) 233 (071) 143 (043) 206 (032) 005 (001) 018 (004)P-N fen -LTD 2 1975 (347) 2848 (762) 035 (005) 127 (027) 057 (002) 108 (007) 004 (002) 010 (0001)P-N bog -PR 2 967 (120) 1192 (185) 049 (021) 056 (016) 057 (023) 072 (018) 004 (004) 012 (005)P-N bog -STD 2 1147 (072) 1209 (129) 035 (002) 041 (003) 036 (001) 060 (018) 004 (001) 008 (002)P-N bog -LTD 2 2056 (080) 4707 (1663) 036 (003) 084 (045) 048 (005) 109 (050) 008 (001) 016 (014)SFA fen -PR 3 579 (164) 051 (008) 112 (022) 281 (044) 113 (016) 263 (051) 775 (144) 034 (020)SFA fen -STD 3 325 (143) 128 (029) 440 (163) 377 (008) 332 (094) 309 (042) 026 (017) 004 (004)SA fen -LTD 3 1780 (1002) 1834 (560) 032 (008) 036 (013) 044 (012) 052 (023) 0 0SA bog -LTD 3 1960 (309) 361 (100) 027 (001) 069 (003) 036 (001) 091 (003) 0 0SB bog -PR 3 659 (234) 064 (020) 025 (013) 046 (005) 031 (014) 054 (004) 0 0SB bog -STD 3 882 (626) 153 (035) 050 (016) 040 (002) 058 (016) 051 (004) 0 0SFC bog -PR 2 592 (343) 271 (053) 030 (014) 044 (002) 034 (017) 056 (005) 0 0SFC bog -STD 2 819 (632) 310 (0001) 031 (011) 037 (003) 034 (012) 046 (005) 0 0SFC bog -LTD 2 2893 (962) 1395 (024) 021 (002) 020 (001) 025 (004) 026 (004) 0 0

Table A1 Continued

PA mass loss pH

phosphomonoesterase phosphodiesteraselitter type nutrient and WT regime n yr1 yr2 yr1 yr2 yr1 yr2 yr1 yr2

CL-L fen -PR 2 7410 (2635) 13017 (6366) 2323 (085) 2685 (266) 2318 (682) 3885 (159) 564 (016) 512 (064)CL-L fen -STD 2 19539 (3892) 16158 (3853) 2808 (1837) 2161 (486) 3620 (265) 4824 (1268) 531 (021) 527 (044)BN-L fen -PR 3 4608 (441) 6454 (1762) 636 (073) 797 (064) 3617 (151) 4535 (216) 467 (004) 481 (007)BN-L fen -STD 3 10928 (5171) 10582 (6331) 889 (246) 992 (489) 3514 (501) 5367 (1291) 554 (018) 565 (022)BN-L fen -LTD 3 10232 (1581) 11941 (8477) 968 (215) 1191 (751) 4134 (391) 5318 (773) 415 (021) 565 (014)BN-L bog -PR 3 10483 (1191) 16938 (733) 964 (071) 1770 (426) 4028 (400) 5054 (837) 480 (053) 485 (018)BN-L bog -STD 3 10747 (1323) 16976 (2618) 1476 (297) 1840 (396) 4386 (167) 6229 (522) 447 (005) 479 (007)BN-L bog -LTD 3 8850 (911) 8859 (2813) 996 (138) 679 (175) 4269 (521) 6022 (647) 452 (006) 453 (019)P-N fen -PR 2 6611 (1557) 8264 (1560) 1201 (082) 1518 (152) 3258 (093) 4243 (132) 447 (012) 446 (021)P-N fen -STD 2 8898 (2381) 8797 (084) 1730 (545) 1718 (049) 3291 (424) 5018 (134) 442 (006) 478 (001)P-N fen -LTD 2 8500 (821) 8801 (3590) 1083 (090) 1625 (1 53) 3798 (311) 5472 (101) 415 (028) 403 (015)P-N bog -PR 2 4418 (497) 7253 (154) 801 (190) 913 (130) 3243 (024) 4934 (103) 465 (009) 428 (016)P-N bog -STD 2 4300 (357) 7294 (850) 884 (069) 948 (062) 3021 (058) 4621 (274) 439 (013) 429 (018)P-N bog -LTD 2 3655 (140) 11536 (4034) 888 (026) 886 (368) 3659 (106) 5335 (787) 353 (007) 365 (017)SFA fen -PR 3 41644 (2173) 5738 (893) 2676 (402) 421 (077) 1607 (068) 2530 (155) 394 (002) 376 (016)SFA fen -STD 3 20800 (14091) 5320 (1262) 1409 (840) 409 (055) 3290 (369) 4232 (848) 497 (023) 418 (010)SA fen -LTD 3 21712 (7780) 17954 (6204) 1022 (405) 1346 (443) 2706 (164) 3022 (1026) 446 (003) 447 (005)SA bog -LTD 3 28732 (1872) 5257 (888) 1448 (096) 303 (026) 2655 (111) 4273 (206) 405 (003) 406 (005)SB bog -PR 3 9703 (3306) 2882 (430) 1239 (501) 475 (031) 1491 (051) 1944 (277) 446 (050) 384 (013)SB bog -STD 3 9511 (5426) 5147 (207) 740 (416) 510 (141) 2136 (042) 2625 (283) 485 (005) 452 (013)SFC bog -PR 2 7492 (5078) 3683 (610) 1002 (704) 427 (023) 1621 (165) 2360 (058) 450 (024) 457 (014)SFC bog -STD 2 15121 (10343) 5313 (144) 885 (627) 444 (001) 1675 (031) 2355 (321) 410 (017) 413 (019)SFC bog -LTD 2 26031 (1384) 19128 (5949) 1508 (357) 1076 (045) 1918 (154) 2651 (106) 397 (019) 385 (011)

AA actual activities PA potential activities (see Material and Methods)n number of samples per litter type and nutrient andor water table(WT) regime yr1 litter decomposing for one year yr2 litter decomposing for two years WT regimes LTD long-term WT drawdownPR pristine STD short-term WT drawdown Litter types BN-LBetula nanaleaves CL-LCarex lasiocarpaleaves P-NPinus sylvestrisneedles SASphagnum angustifolium SBS balticum SFAS fallax SFCS fuscum



5 Conclusions

We combined analyses of litter quality litter decompositionrates microbial community composition and extracellularenzyme activities to estimate how WT drawdown may affectlitter decomposition and element cycling in a range of peat-land sites differing in soil nutrient availability These factorshave never before been examined simultaneously

Litter type was the main factor shaping the patterns of en-zyme activities and overruled the direct effects of WT draw-down on aerobic microbial activity Our results imply thatchange in the structure of plant communities in response topersistent WT drawdown will strongly affect the C dynam-ics of peatlands The dynamics of plant community compo-sition and consequent litterfall need to be considered alongwith soil factors when estimating the impacts of global cli-mate change on C cycling in peatlands The soil factors needto include pH since that also changes along with persistentWT drawdown

Enzyme activities generally turned from N and P acqui-sition towards C acquisition following the long-term WTdrawdown suggesting reduced nutrient limitation of decom-posers Decomposers then seemed to invest into C-acquiringenzymes that produced high litter decomposition rates

Sphagnummosses exhibited low enzyme activities and de-composed slowly compared to vascular plants Yet we ob-served abundant fine root growth and an enzyme activity al-location shift towards P acquisition This may have beeninduced by the roots of arboreal plants and suggests thatmosses or their degradation products may be used as a sub-strate by trees and shrubs SinceSphagnumis generally con-sidered to be a hostile environment this feature would de-serve further study

Coupled with the findings of earlier research our observa-tions suggest that different factors regulate microbial activityin peat and in the litter that contributes new C to this im-portant pool These factors also vary between bog and fensites Thus C cycling in litter and in peat should be exam-ined separately in order to improve our understanding of Cdynamics under changing environmental conditions (see alsoLaiho 2006) To further complicate reaching clear conclu-sions about peatland responses to climate change our resultsemphasize that bogs and fens may respond in different man-ners and that there may be notable spatial variation relatedto plant community composition

Our results emphasize the importance of considering thetime-scale of the environmental changes The effects of envi-ronmental changes on soil processes are getting dominant inthe long-term following the dramatic changes in vegetationcomposition (indirect effect of the environmental changes)

AcknowledgementsThis study was supported by the Academyof Finland (projects 104425 and 106197) a Royal Society Inter-national Collaboration Grant the European Science Foundationand the Graduate School of Forest Sciences We thank KaisaHeinonen Nathalie Fenner Tim Jones Tim Ellis and Satu Repofor their valuable help with the laboratory work Juul Limpens andBjorn Berg for their thorough and constructive comments on themanuscript and Michael Hardman for revising the language

Edited by D Zona

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Allison S D and Vitousek P M Extracellular enzyme activitiesand carbon chemistry as drivers of tropical plant litter decompo-sition Biotropica 36 285ndash296 2004

Anttila J Lyhyt- ja pitkaaikaisen kuivatuksen aiheuttamat muu-tokset soiden maanpaallisen karikkeen tuotossa [Effects of short-term and long-term water-level drawdown on the above-groundlitter inputs into peatland ecosystems] MSc thesis Departmentof Forest Ecology University of Helsinki Finland 56 pp 2008

Borga P Nilsson M and Tunlid A Bacterial communities inpeat in relation to botanical composition as revealed by phos-pholipid fatty acid analysis Soil Biol Biochem 26 841ndash8481994

Bragazza L Siffi C Iacumin P and Gerdol R Mass loss andnutrient release during litter decay in peatland The role of mi-crobial adaptability to litter chemistry Soil Biol Biochem 39257ndash267 2007

Breeuwer A J G Robroek B J M Limpens J Heijmans MM P D Schouten M G C and Berendse F Decreased sum-mer water table depth affects peatland vegetation Basic ApplEcol 10 330ndash339 2009

Cole J R Chai B Farris R J Wang Q Kulam S A Mc-Garrell D M Garrity G M and Tiedje J M The Ribo-somal Database Project (RDP-II) sequences and tools for high-throughput rRNA analysis Nucleic Acids Research 33 (DatabaseIssue) D294ndashD296 2005

Cornelissen J H van Bodegom P M Aerts R Callaghan TV van Logtestijn R S Alatalo J Chapin F S Gerdol RGudmundsson J Gwynn-Jones D Hartley A E Hik D SHofgaard A Jonsdottir I S Karlsson S Klein J A Laun-dre J Magnusson B Michelsen A Molau U OnipchenkoV G Quested H M Sandvik S M Schmidt I K Shaver GR Solheim B Soudzilovskaia N A Stenstrom A TolvanenA Totland Oslash Wada N Welker and J M Zhao Global neg-ative vegetation feedback to climate warming responses of leaflitter decomposition rates in cold biomes Ecol Lett 10 619ndash627 2007

Corstanje R and Reddy K R Response of biogeochemical indi-cators to a drawdown and subsequent reflood J Environ Qual33 2357ndash2366 2004

Domisch T Finer L Laiho R Karsisto M and Laine J De-composition of Scots pine litter and the fate of released carbon inpristine and drained pine mires Soil Biol Biochem 32 1571ndash1580 2000

Dorrepaal E Cornelissen J H C Aerts R Wallen B and vanLogtestijn R S P Are growth forms consistent predictors of



leaf litter quality and decomposability across peatlands along alatitudinal gradient Jour Ecol 93 817ndash828 2005

Farrish K W and Grigal D G Decomposition in an om-brotrophic bog and a minerotrophic fen in Minnesota Soil Sci145 353ndash358 1988

Fenner N Freeman C and Reynolds B Hydrological effects onthe diversity of phenolic degrading bacteria in a peatland impli-cations for carbon cycling Soil Biol Biochem 37 1277ndash12872005a

Fenner N Freeman C and Reynolds B Observations of a sea-sonally shifting thermal optimum in peatland carbon-cycling pro-cesses implications for the global carbon cycle and soil enzymemethodologies Soil Biol Biochem 37 1814ndash1821 2005b

Fisk M C Ruether K F and Yavitt J B Microbial activ-ity and functional composition among northern peatland ecosys-tems Soil Biol Biochem 35 591ndash602 2003

Freeman C Liska G Ostle N J Jones S E and Lock M AThe use of fluorogenic substrates for measuring enzyme activityin peatlands Plant Soil 175 147ndash152 1995

Freeman C Ostle N and Kang H An enzymic rsquolatchrsquo on aglobal carbon store Nature 409 149 2001

Freeman C Ostle N J Fenner N and Kang H A regulatoryrole for phenol oxidase during decomposition in peatlands SoilBiol Biochem 36 1663ndash1667 2004

Gholz H L Wedin D A Smitherman S M Harmon M Eand Parton W J Long-term dynamics of pine and hardwoodlitter in contrasting environments toward a global model of de-composition Glob Change Biol 6 751ndash765 2000

Gianfreda L and Bollag J M Influence of natural and anthro-pogenic factors on enzyme activity in soil in Soil Biochemistryedited by Stotzky G and Bollag J M Mercel Dekker NewYork 123ndash193 1996

Gitay H Brown S Easterling W Jallow B Antle J AppsM J Beamish R Chapin T Cramer W Frangi J LaineJ Erda L Magnuson J Noble I Price J Prowse T RootT Schulze E Sirotenko O Sohngen B and Soussana JEcosystems and their goods and services in Climate Change2001 Impacts Adaptation and Vulnerability edited by Mc-Carthy J J Canziani O F Leary N A Dokken D J andWhite K S Cambridge University Press Cambridge 235-3422001

Gorham E Northern peatlands role in the carbon cycle and prob-able responses to climatic warming Ecol Appl 1 182ndash1951991

Grieve I C Gilvear D G and Bryant R G Hydrochemical andwater source variations across a floodplain mire Insh MarshesScotland Hydrol Process 9 99ndash110 1995

Gusewell S and Freeman C Phosphorus-limited decompositionof litter from phosphorus-limited plants grown in strong sunlightFunct Ecol 19 582-593 2005

Hajek T Ballance S Limpens J Zijlstra M and Verhoeven JT A Cell-wall polysaccharides play an important role in decayresistance ofSphagnumand actively depressed decomposition invitro Biogeochemistry 103 45ndash57 2011

Hernandez D L and Hobbie S E The effects of substrate com-position quantity and diversity on microbial activity Plant Soil335 397ndash397 2010

Hobbie S E Temperature and plant species control over litterdecomposition in Alaskan tundra Ecol Monogr 66 503ndash522

1996Hobbie S E and Gough L Litter decomposition in moist acidic

and non-acidic tundra with different glacial histories Oecologia140 113ndash124 2004

Hughes S Dowrick D J Freeman C Hudson J A andReynolds B Methane emissions from a gully mire in mid-Wales UK under consecutive summer water table drawdownEnviron Sci Technol 33 362ndash365 1999

Hunt H W Ingham E R Coleman D C Elliot E T and ReidC P P Nitrogen limitation of production and decomposition inprairie mountain meadow and pine forest Ecology 69 1009ndash1016 1988

Jaatinen K Fritze H Laine J and Laiho R Effects of short-and long-term water-level drawdown on the populations and ac-tivity of aerobic decomposers in a boreal peatland Glob ChangeBiol 13 491ndash510 2007

Jaatinen K Laiho R Vuorenmaa A del Castillo U Minkki-nen K Pennanen T Penttila T and Fritze H Responsesof aerobic microbial communities and soil respiration to a water-level drawdown in a northern boreal fen Environ Microbiol 10339ndash353 2008

Kang H and Freeman C Phosphatase and arylsulphatase activ-ities in wetland soils annual variation and controlling factorsSoil Biol Biochem 31 449ndash454 1999

Korkama-Rajala T Muller M and Pennanen T Decompositionand fungi of needle litter from slow- and fast-growing Norwayspruce (Picea abies) clones Microbial Ecol 56 76ndash89 2008

Kubartova A Moukoumi J Beguiristain T Ranger J andBerthelin J Microbial diversity during cellulose decompositionin different forest stands I Microbial communities and environ-mental conditions Microbial Ecol 54 393ndash405 2007

Kurz-Besson C Couteaux M M Thiery J M Berg B andRemacle J A comparison of litterbag and direct observationmethods of Scots pine needle decomposition measurement SoilBiol Biochem 37 2315ndash2318 2005

Laiho R Vasander H Penttila T and Laine J Dynamicsof plant-mediated organic matter and nutrient cycling followingwater-level drawdown in boreal peatlands Global BiogeochemCy 17 1053 doi1010292002GB002015 2003

Laiho R Decomposition in peatlands Reconciling seeminglycontrasting results on the impacts of lowered water levels SoilBiol Biochem 38 2011ndash2024 2006

Laine J Vasander H and Laiho R Long-term effects of waterlevel drawdown on the vegetation of drained pine mires in south-ern Finland J Appl Ecol 32 785ndash802 1995a

Laine J Vasander H and Sallantaus T Ecological effects ofpeatland drainage for forestry Environ Rev 3 286ndash303 1995b

Laine J Komulainen V-M Laiho R Minkkinen K Ras-inmaki A Sallantaus T Sarkkola S Silvan N TolonenK Tuittila E-S Vasander H and Paivanen J Lakkasuo ndasha guide to mire ecosystem Department of Forest Ecology Publi-cations University of Helsinki 31 123 pp 2004

Limpens J Berendse F Blodau C Canadell J G FreemanC Holden J Roulet N Rydin H and Schaepman-StrubG Peatlands and the carbon cycle from local processes toglobal implications - a synthesis Biogeosciences 5 1475ndash1491doi105194bg-5-1475-2008 2008

Leps J andSmilauer P Multivariate analysis of ecological datausing CANOCO Cambridge University Press Cambridge 2003



Minkkinen K Byrne K A and Trettin C Climate impacts ofpeatland forestry in Peatlands and climate change edited byStrack M International Peat Society Jyvaskyla 98ndash122 2008

Minkkinen K Laine J and Hokka H Tree stand developmentand carbon sequestration in drained peatland stands in Finland ndasha simulation study Silva Fenn 35 55ndash69 2001

Nannipieri P Kandeler E and Ruggiero P Enzyme activitiesand microbiological and biochemical processes in soil in En-zymes in the Environment Activity Ecology and Applicationseduted by Burns R G and Dickand R P Marcel Dekker NewYork 1ndash33 2002

Niemi R M and Vepsalainen M Stability of the fluorogenic en-zyme substrates and pH optima of enzyme activities in differentFinnish soils J Microbiol Meth 60 195ndash205 2005

Nubel U Engelen B Felske A Snaidr J Wieshuber AAmann R I Ludwig W and Backhaus H Sequence het-erogeneities of genes encoding 16S rRNAs inPaenibacilluspolymyxadetected by temperature gradient gel electrophoresisJ Bacteriol 178 5636ndash5643 1996

Peltoniemi K Aerobic carbon-cycle related microbial commu-nities in boreal peatlands responses to water-level drawdownDissertationes Forestales 101 Finnish Society of Forest Sci-ence Helsinki 54 phttpwwwmetlafidissertationesdf101htm 2010

Peltoniemi K Fritze H and Laiho R Response of fungal andactinobacterial communities to water-level drawdown in borealpeatland sites Soil Biol Biochem 41 1902ndash1914 2009

Pennanen T Caul S Daniell T J Griffiths B S Ritz K andWheatley R E Community-level responses of metabolically-active soil microorganisms to the quantity and quality of sub-strate inputs Soil Biol Biochem 36 841ndash848 2004

Rejmankova E and Sirova D Wetland macrophyte decomposi-tion under different nutrient conditions relationships betweendecomposition rate enzyme activities and microbial biomassSoil Biol Biochem 39 526ndash538 2007

Robroek B J M Limpens J Breeuwer A and Schouten MG C Effects of water level and temperature on performance offour Sphagnummosses Plant Ecol 190 97ndash107 2007

Romanı A M Fischer H Mille-Lindblom C and Tranvik L JInteractions of bacteria and fungi on decomposing litter Differ-ential extracellular enzyme activities Ecology 87 2559ndash25692006

Roulet N Moore T Bubier J and Lafleur P Northern fensmethane flux and climatic change Tellus 44B 100ndash105 1992

Sarkkola S Hokka H Koivusalo H Nieminen M Ahti EPaivanen J and Laine J Role of tree stand evapotranspirationin maintaining satisfactory drainage conditions in drained peat-lands Can J For Res 40 1485ndash1496 2010

Schlotzhauer S M and Price J S Soil water flow dynamics in amanaged cutover peat field Quebec Field and laboratory inves-tigations Water Resour Res 35 3675ndash3683 1999

Schulze E D and Freibauer A Carbon unlocked from soils Na-ture 437 205ndash206 2005

Sinsabaugh R L Enzymic analysis of microbial pattern and pro-cess Biol Fertil Soils 17 69ndash74 1994

Sinsabaugh R L Carreiro M M and Repert D A Allocationof extracellular enzymatic activity in relation to litter composi-tion N deposition and mass loss Biogeochemistry 60 1ndash242002

Strakova P Anttila J Spetz P Kitunen V Tapanila Tand Laiho R Litter quality and its response to water leveldrawdown in boreal peatlands at plant species and communitylevel Plant Soil 335 501ndash520doi101007s11104-010-0447-62010 2010

Strickland M S Osburn E Lauber C Fierer N and BradfordM A Litter quality is in the eye of the beholder initial decom-position rates as a function of inoculum characteristics FunctEcol 23 627ndash636 2009

Suding K N Lavorel S Chapin F S Cornelissen H DiazS Garnier E Goldberg D Hooper D U Jackson S Tand Navas M L Scaling environmental change through thecommunity-level a trait-based response-and-effect frameworkfor plants Glob Change Biol 14 1125ndash1140 2008

Tabatabai M A Soil enzymes in Methods of Soil AnalysesPart 2 Microbiological and Biochemical Properties edited byWeaver R W Angle J S and Bottomly P S Soil ScienceSociety of America Madison WI USA 775ndash833 1994

Taylor B R Air-drying depresses rates of leaf litter decomposi-tion Soil Biol Biochem 30 403ndash412 1998

ter Braak C J F andSmilauer P CANOCO Reference Manualand CanoDraw for Windows Userrsquos guide Software for Canoni-cal Community Ordination (version 45) Microcomputer PowerIthaca USA 2002

Thormann M N Diversity and function of fungi in peatlands Acarbon cycling perspective Can J Soil Sci 86 281ndash293 2006

Thormann M N Bayley S E and Currah R S Microcosm testsof the effects of temperature and microbial species number on thedecomposition ofCarex aquatilisand Sphagnum fuscumlitterfrom southern boreal peatlands Can J Microbiol 50 793ndash8022004

Toberman H Laiho R Evans C Artz R Fenner N StrakovaP and Freeman C Long-term drainage for forestry inhibitsextracellular phenol oxidase activity in Finnish boreal mire peatEur J Soil Sci 61 950ndash957 2010

Vainio E J and Hantula J Direct analysis of wood-inhabitingfungi using denaturing gradient gel electrophoresis of amplifiedribosomal DNA Mycol Res 104 927ndash936 2000

Vepsalainen M Erkomaa K Kukkonen S Vestberg M Wal-lenius K and Niemi R M The impact of crop plant cultiva-tion and peat amendment on soil microbial activity and structurePlant Soil 264 273ndash286 2004

Vepsalainen M Kukkonen S Vestberg M Sirvio H andNiemi R M Application of soil enzyme activity test kit in afield experiment Soil Biol Biochem 33 1665ndash1672 2001

Weltzin J F Bridgham S D Pastor J Chen J Q and HarthC Potential effects of warming and drying on peatland plantcommunity composition Glob Change Biol 9 141ndash151 2003

Weltzin J F Pastor J Harth C Bridgham S D Updegraff Kand Chapin C T Response of bog and fen plant communitiesto warming and water-table manipulations Ecology 81 3464ndash3478 2000



1 Introduction

Peatlands are a significant atmospheric carbon (C) sink dueto a long-term imbalance between litter production and de-composition This imbalance is caused by high water tables(WT) and consequent anoxia that slows down decomposition(eg Gorham 1991 Schulze and Freibauer 2005) Globalclimate change is predicted to result in lowered WT in north-ern peatlands (Gorham 1991 Roulet et al 1992 Gitay etal 2001) via changes in precipitation patterns andor in-creased temperature and evapotranspiration Another impor-tant issue is currently the C balance of peatlands drained forforestry by ditching which is the most extensively appliedland-use practise on peatlands of Nordic countries and Rus-sia (Minkkinen et al 2008) Because peatlands representa large portion of the terrestrial C pool it is important tounderstand their role in the global C cycle and predict theirresponse to climate andor land-use change (Limpens et al2008)

Persistent lowering of the WT promotes several changesin peatland environmental conditions (Laiho 2006) that mayhave direct effects on decomposition Decreased water con-tent in the surface peat and increased soil aeration maystimulate the activity of aerobic decomposers Increasedpeat compaction may in turn slow down their activityDirect effects of WT drawdown on the current vegetationcover include changes in nutrient concentrations because ofchanges in nutrient availability or root functioning Howeverany direct effects may be overruled by the indirect effectsthrough changes in plant community structure (Dorrepaal etal 2005) These effects have not yet been thoroughly evalu-ated

A persistent change in the WT affects plant communitystructure (Weltzin et al 2000 2003 Robroek et al 2007Breeuwer et al 2009) and eventually can lead to a completeturnover of species adapted to the new conditions (Laineet al 1995a) Such changes tend to be more pronouncedin nutrient-rich sites and intensify over time (Laine et al1995a) In consequence the quantity and quality of plantlitter produced after the long-term WT drawdown greatly dif-fer from that produced under pristine conditions (Laiho et al2003 Strakova et al 2010) Such changes may have impor-tant consequences for soil C dynamics (eg Hobbie 1996Dorrepaal et al 2005 Cornelissen et al 2007 Suding et al2008)

The structure of the peatland microbial community varieswith the plant community (Borga et al 1994 Fisk et al2003 Thormann et al 2004 Jaatinen et al 2007 2008)and it has been shown that changes in peatland hydrologyaffect both (Jaatinen et al 2007 Peltoniemi et al 2009)Microbial responses in the form of enzyme activities havebeen detected (Fenner et al 2005a Toberman et al 2010)and may be directly induced by the increased availabilityof oxygen andor changes in pH The presence of bimolec-ular oxygen activates phenol oxidase enzymes that degrade

highly recalcitrant polyphenolic compounds Phenol oxidasemay also activate extracellular hydrolase enzymes by theirrelease from phenolic inhibition the ldquoenzymic latch theoryrdquo(Freeman et al 2001 2004) Decomposition is a summativeeffect of several enzymes produced by the microbial commu-nity and changes in the quality and quantity of litter inputsmay affect the activity of each enzyme in a unique manner(Hernandez and Hobbie 2010)

Indirect effects of WT drawdown on the composition andactivity of aerobic microbial decomposers in peatlands viachanges in plant community structure are in spite of theirsignificance still poorly understood (Laiho 2006 Thor-mann 2006) Furthermore soil nutrient availability may in-fluence community-level decomposition processes (Hobbieand Gough 2004) Plant communities and consequently lit-ter qualities vary along with environmental factors such asWT soil pH and nutrient availability that can affect differentspecies in different ways (Hobbie and Gough 2004) Con-sequently it is difficult to predict changes in decompositionrates in situations where the plant community andor soil fac-tors are changing As a first step we focus on the relative im-portance of substrate quality soil conditions and microbialcommunity composition on microbial activity

The aim of our study was thus to disentangle (1) direct and(2) indirect effects of WT drawdown on the activity of aer-obic microbial decomposers in boreal peatland ecosystemsand to link the activity to microbial community compositionlitter quality and litter decomposition rates We characterizedmicrobial activity by quantifying 11 extracellular enzymesinvolved in mineralization of organic C nitrogen (N) phos-phorus (P) and sulphur (S) in selected litter types typical ofour sites at two stages of decomposition By this we aimedto capture both spatial (litter type) and temporal (decompo-sition stage) variation in microbial activity The selection ofC- N- and P-acquiring enzymes was based on previous stud-ies aiming to include enzymes that play principal roles in theprocess of organic matter decomposition (eg Sinsabaugh1994 Allison and Vitousek 2004 Vepsalainen et al 2004Fenner et al 2005b Rejmankova and Sirova 2007) Addi-tionally we included the S-acquiring enzyme arylsulphatasean important enzyme of wetland soils (Kang and Freeman1999 Rejmankova and Sirova 2007)

We hypothesized that WT drawdown has (1) direct pos-itive effects on microbial enzyme activities caused by im-proved environmental conditions for aerobic decomposersand (2) indirect effects via changes in plant communitystructure and thus litter quality as the substrate for decom-posers Following WT drawdown direct effects will be ob-served as an increase in microbial enzyme activity in lit-ter types common to all WT regimes Indirect effects willbe observed as variation in enzyme activity allocation (stan-dardized activities of each enzyme within a sample) betweenthe different litter types reflecting the changes in the plantcommunities Furthermore we hypothesized that (3) therelatively nutrient-rich fen will have a higher production of






21 Study sites






Fen Bog

















24 Enzyme assays


























c = Aεl (1)






26 Data analyses


















3 Results

31 General patterns


















4 Discussion




















422 Site effect









AA



Table A1 Continued

PA





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Table A1 Continued

PA mass loss pH






5 Conclusions








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21 Study sites






Fen Bog

















24 Enzyme assays


























c = Aεl (1)






26 Data analyses


















3 Results

31 General patterns


















4 Discussion




















422 Site effect









AA



Table A1 Continued

PA





Table A1 Continued

PA



Table A1 Continued

PA mass loss pH






5 Conclusions








Edited by D Zona

References
























































































24 Enzyme assays


























c = Aεl (1)






26 Data analyses


















3 Results

31 General patterns


















4 Discussion




















422 Site effect









AA



Table A1 Continued

PA





Table A1 Continued

PA



Table A1 Continued

PA mass loss pH






5 Conclusions








Edited by D Zona

References



































































































c = Aεl (1)






26 Data analyses


















3 Results

31 General patterns


















4 Discussion




















422 Site effect









AA



Table A1 Continued

PA





Table A1 Continued

PA



Table A1 Continued

PA mass loss pH






5 Conclusions








Edited by D Zona

References























































































3 Results

31 General patterns


















4 Discussion




















422 Site effect









AA



Table A1 Continued

PA





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PA



Table A1 Continued

PA mass loss pH






5 Conclusions








Edited by D Zona

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4 Discussion




















422 Site effect









AA



Table A1 Continued

PA





Table A1 Continued

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Table A1 Continued

PA mass loss pH






5 Conclusions








Edited by D Zona

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422 Site effect









AA



Table A1 Continued

PA





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Table A1 Continued

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5 Conclusions








Edited by D Zona

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AA



Table A1 Continued

PA





Table A1 Continued

PA



Table A1 Continued

PA mass loss pH






5 Conclusions








Edited by D Zona

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Table A1 Continued

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Table A1 Continued

PA mass loss pH






5 Conclusions








Edited by D Zona

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5 Conclusions








Edited by D Zona

References

















































































Litter type affects the activity of aerobic decomposers in a boreal ...

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