Amanda Brennan 1, Elise Pendall 1, Dave Risk 2, Yolima Carrillo 3 1 University of Wyoming,...
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Transcript of Amanda Brennan 1, Elise Pendall 1, Dave Risk 2, Yolima Carrillo 3 1 University of Wyoming,...
Amanda Brennan1, Elise Pendall1, Dave Risk2, Yolima Carrillo3
1 University of Wyoming, Department of Botany and Program in Ecology, Laramie, WY 82071, contact: [email protected] 2 Dept. of Earth Sciences, St. Francis Xavier University, Antigonish, NS, Canada; 3 University of Sydney, Australia
AcknowledgementsWe thank Dan LeCain and Jack Morgan for technical support. This project was supported by USDA-CSREES Soil Processes Program , DOE and NSF, with travel support from UW Program in Ecology and Department of Botany.
B51B-0547
Continuous soil respiration at the Prairie Heating and CO2 Enrichment site using forced diffusion chambers
Introduction
Variation in soil respiration is regulated by plant and microbial
responses to environmental changes, such as soil moisture. Our first
objective was to determine the reliability of forced diffusion chambers
housing non-dispersive infrared CO2 sensors for continuous fluxes in
semi-arid grasslands (Risk et al. 2011). We also compared the
response of soil respiration to environmental drivers under different
climatic treatments. We hypothesized that elevated CO2 would
stimulate both total soil and microbial respiration, due to increased
belowground allocation, whereas warming would reduce soil and
microbial respiration as a result of soil drying. We further hypothesized
that total soil respiration would be more sensitive to soil moisture,
whereas microbial respiration in the plant-free plots would be more
sensitive to changes in soil temperature.
Study site• Prairie Heating and CO2 Enrichment (PHACE) is located in northern mixed-grass prairie near Cheyenne, WY, USA (http://www.ars.usda.gov/npa/rrru/phace) • Vegetation dominated by cool season (C3) grasses with an important warm season (C4) species• Mean annual precipitation is 370 mm; mean temperature is 7°C• PHACE rings are 3-m diameter, elevated [CO2] is raised to 600 ppm by direct injection in daytime during the growth season, and temperature is warmed to +1.5/+3°C day/night year-round with ceramic heaters. [CO2] treatment started in 2006, warming in 2007.
Observations
Conclusions and Future Work•Prairie soil respiration was not consistently affected by climate change treatments, but was largely influenced by environmental drivers.•Treatment effects were stronger on microbial respiration with less effects of environmental drivers.•The drift in CO2 concentration over time needs to be addressed before flux-driver relationships can be better understood.
Infra-red Heaters
Free Air CO2 Enrichment Ring
PHACE Treatments
ct = ambient [CO2] and temperature
cT = ambient [CO2] and elevated temperature
Ct = elevated [CO2] and ambient temperature.
Soil Efflux and Environmental Controls
CO2 ConcentrationsContinuous Timeseries- Forced Diffusion•Soil Emissions pass into a dynamic chamber along a slightly restrictive membrane with known diffusivity; background air is monitored in a chamber sealed off from the soil•Vaisala GMP-222 IRGAs inside the chambers continuously measure [CO2]
Plant-free plots had glyphosate added in May 2008 and a root barrier to 25 cm is maintained by manual removal.
Daily Averages for Background Air [CO2]
[CO
2]
pp
m
400
500
600
700
800
900 CtcTct
Daily averages for plant-free chamber [CO2]
[CO
2]
pp
m
400
500
600
700
800
900
Daily averages for mixed grass prairie chamber [CO2]
Day of Year
0 100 200 300
[CO
2]
pp
m
400
500
600
700
800
900
ReferencesRisk D, Nickerson N, Creelman C, McArthur G, Owens J (2011). Forced Diffusion soil flux: A new technique for continuous monitoring of soil gas efflux. Agricultural and Forest Meteorology 151: 12, 1622-1631.
Mixed grass prairie soil respiration
Soil
Re
sp
iratio
n (
mo
l m-2
s-1)
2
4
6
8
10
12
14
Plant-free soil respiration
Soil
Re
sp
iratio
n (
mo
l m-2
s-1)
2
4
6
8
10
12
14
CtcTct
Soil Temperature at 3 cm depth
Tem
pera
ture
o C
-10
0
10
20
30
Volumetric Water Content at 0-10 cm
Day of Year
0 100 200 300
VW
C (
%)
4
6
8
10
12
14
16
18
20
22
Risk et al. 2011
Mixed-grass chamber
Plant-free chamber
Air Chamber