SER – Summer School 2009 – Münster University Department Biology Hamburg University The...

SE

R –

Sum

mer

Sch

ool 2

009

– M

ünst

er U

nive

rsity

Department Biology

HamburgUniversity

The (potential) role of seed ecology in restoration:

Germination, seed banks and establishment

Kai Jensen

Applied Plant Ecology

University of Hamburg

[email protected]

Outline

Introduction

Germination

• Influence of abiotic factors

Persistence and Seed Banks

• Primary and secondary dormancy

• Seed bank types

Dispersal

• Hydrochorous seed transport

Establishment

• Seed- versus microsite-limitation

Summary and conclusions

02.07.09Kai Jensen SER Summer School 2009

ConclusionsEstablishmentSeed banksGerminationIntroduction Dispersal

1000 m

1950

1985

2002

Drainage, Eutrophication

Abandonment

Changes of fen grassland area and distribution

(1950 – 2002; Lake Vollstedt, Northern Germany



Yacoub (2002)

Seed banks and succession in changing landscapes

You have only to dig a pond anywhere … and you will soon have … the usual waterplants (Thoreau 1860)

• Early phase of farm abandonment in New England

• Forest recovery

You have only to restore the site conditions including a proper hydroregime anywhere and you will soon have the usual wetland species

• Application of fertilizers led to an eutrophication of the landscape

• Widespread land use has greatly homogenized formerly dissimilar habitats

• Human development and land-use changes are accompanied with habitat fragmentation



Questions

Are seed banks and seedling establishment important for the conservation and/or restoration of wetlands?

Which factors affect the longevity of seeds in the soil?

• Germination requirements?

• Dormancy pattern?

• Seed morphology (weight, shape)?

Which factors affect hydrochorous dispersal?

• Seed buyoancy?

• Seed production?

Which factors limit the establishment of species in wetlands?

• Seed availability (seed banks, seed dispersal)?

• Microsite availability (gaps, disturbance)?



Germination Ecology

Germination is a complex process which includes the imbibition of water, an increase in respiration activity, the mobilization of nutrient reserves and the initiation of growth in the embryo. Finally, germination results in the bursting of the testa and the extrusion of the plumule or radicle.

How is germination of wetland species affected by abiotic factors?

• Temperature and temperature fluctuations

• Light quantity and light quality

• Salinity

Do germination requirements of individual wetland species vary?

• Within individuals?

• Among populations?

• Temporally?



Temperature and germination

Patzelt et al. (2001)

Silene flos-cuculi

Senecio aquaticus

0

20

40

60

80

100

0

20

40

60

80

100

Ger

min

atio

n [

%]

Temperature [°C]

Methods

• Dry-stored seeds

• Constant tempe-ratures (3 – 35°C)

• Fluctuating tempe-ratures (5/15°C; 10/25°C)

• Diurnal light regime



Temperature fluctuations and germination

Schütz (1999)

Carex elongata

Carex elata

Ger

min

atio

n [

%]

0

20

40

60

80

100

0 2 4 6 8 10 12 14 16

light

darkness

0

20

40

60

80

100

0 2 4 6 8 10 12 14 16

Amplitude [°C]

Methods

• Dry-stored seeds

• Daily fluctuating temperatures (amplitudes from 0 – 16°C)

• Mean temperature 22°C



Canopy effects on light quantity and quality

Above leaf-canopy

• red : far-red = 1.2

Below leaf-canopy

• red : far-red = 0.18

PFRPR

R660

FR730

germi-nation

Phytochrome-System



Pons (19xy)

Light quality and germination

Maas (1989)

0

20

40

60

80

100

white dark red far_red

Ge

rmin

ati

on

[%

]

0

20

40

60

80

100

white dark red far_red

Ge

rmin

ati

on

[%

]

Primula farinosa

Tofieldia calyculata



Seed mass and light-requirement for germination

Seed mass [mg]

Pro

po

rtio

n o

f g

erm

inat

ion

in d

arkn

ess

inre

lati

on

to

ger

min

atio

n in

lig

ht

[%]

0

20

40

60

80

100

0.01 0.10 1.00 10.00

r = 0.57 p < 0.001

Jensen & Gutekunst (2003)



Germination in light and in darkness

0.00

0.20

0.40

0.60

0.80

1.00

Maas (1989)

Jensen(1999)

Jensen &Gutekunst(in press)

Schütz &Rave(1999)

total

unaffected

promoted by light

N = 25 17 35 23 100

(2003)



Variation of germination within single inflorescences

0

5

10

15

20

25

30

35

40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Days

center

margin

0

5

10

15

20

25

30

35

40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Days

centre

margin

Nu

mb

er o

f g

erm

inat

ed s

eed

s

Days Brändel (2004)

Dispersal ability

low high

Bidens

frondosa

25°C

10/20°C



Temporal changes of germination requirements

0

20

40

60

80

100

oct

dec

feb

apr

jun aug

oct

dec

feb

apr

jun aug

oct

light

darkness

Ger

min

atio

n [

%]

1991 1992 1993

Milberg (1994)

primary dormancy

secondary dormancy

Dormancy release

Dormancy induction

Silene flos-cuculi



Germination ecology and zonation in wetlands

Salinity [%]

Ger

min

atio

n p

erce

nta

ge

0.0 0.7 1.4 2.1 2.8 3.5

0

20

40

60

80

100Elymus athericus

Spartina anglica Germination of both species is

negatively affected by increased salinity

Interaction between species and salinity

Spartina has a higher germination percentage than Elymus at high salinity

Elymus has a higher germination than Spartina at low salinities



Summary: Germination

Most (temperate) wetland species germinate at a wide amplitude of temperatures, but have an optimum between 20 and 30°C

Germination of many wetland species is increased by alternating temperatures, which might restrict germination to the spring

Light requirement for germination is higher in small-seeded species than in large-seeded ones. The light requirement can be interpreted as an adaptation against fatal germination in the soil

Germination requirements vary spatially (within inflorescences, among individuals, among populations) and temporally (dormancy cycles)



Seed persisitence and seed banks

Circumstantial evidence for high longevity of seeds (e.g. Nelumbo nucifera: dried bed of a former lake in NE China; germinating seeds were radiocarbon-dated to be 1288 ± 250 years, Shen-Miller et al. 1995)

Seed densities in the soil vary greatly (1 – 100,000 seeds/m²) between ecosystems

In general, seed density of individual species exponentially declines after it disappeared in the vegetation



Seed bank types

transient

• seed persistence in the soil for less than 1 year

short-term-persistent

• seed persistence in the soil for at least 1 year, but less than 5 years

• play a role in the maintenance of plant populations after a ‚bad year‘ (e.g. poor seed set in a dry year)

long-term persistent

• seed persistence in the soil for at least 5 years

• may contribute to the restoration of destroyed or degraded plant communities



Classification rules for seed bank types

Present in vegetation or vegetation not

described

< 5 years since species last grew at

site

> 4 years since species last grew at

site

Soil layers not subdivided

xxxxxxxxxxxxxxxx

Species absent from the

vegetation x

AT LEAST SHORT-TERM PERSISTENT

xxxxxxxxxx PRESENT

xxxxxx

LONG-TERM PERSISTENT

xx

Soil layers subdivided by

depth xxxxxxxx

Present in the seed bank

xxxxxxxxxxx x

Absent from the seed bank xxxxxxxxxxx

x

SHORT-TERM PERSISTENT

xx

xxxxxxxxxx TRANSIENT

xxxxxx


xx


xxxxxx


site


xx

A SPECIES FOUNDx


described

Present only in surface soil

xxxxxxxxx xxxxxxx

More freq. in upper but

present in lower soil layers

At least as freq. in lower

as in upper soil layers


vegetation x


site

Thompson et al. 1997

Criteria

Presence/absence in vegetation and seed bank

Depth distribution in the soil



Main conclusions of Thompson et al. (1997)

Grassland species have in general a low seed persistence

Rare species have a lower persistence than common ones

Seed size and shape are good predictors of seed persistence

Is that really true??



Dormancy and seed longevity:Burial experiment with seeds of wetland species

Jensen (2004)

Ger

min

atio

n [

%]

Date

0

20

40

60

80

100

Sep Jan May Sep FebNov Mar Jul Nov Apr

Jun

0

20

40

60

80

100

Nov Mar Jul Nov Mar JulJan May Sep Jan May Sep

1997 1998 1999 1996 1997 1998

Mo

rtality [%]

DarknessLight

Mortality

Bromus racemosus Sanguisorba officinalis




Jensen (2004)

Ger

min

atio

n [

%]

Date

0

20

40

60

80

100

0

20

40

60

80

100


1996 1997 1998

Mo

rtality [%]

DarknessLight

Mortality

Rhinanthus angustifolius Pedicularis palustris


1996 1997 1998



Ger

min

atio

n [

%]

Date

0

20

40

60

80

100

0

20

40

60

80

100


1996 1997 1998

Mo

rtality [%]

Viola palustris Carex echinata


1996 1997 1998

DarknessLight

Mortality

Jensen (2004)




Seedbank typeYear 1 Year 2 Year 5 Year 1 Year 2 Year 5

Bromus racemosus 50.0 - - 53.0 100.0 100.0 transientSanguisorba officinalis 90.7 - - 22.7 100.0 100.0 transientSuccisa pratensis 78.8 - - 54.5 100.0 100.0 transient

Angelica sylvestris 63.7 8.3 - 27.1 95.0 100.0 short-term persistentBriza media 98.9 4.2 - 29.9 81.8 100.0 short-term persistentGalium uliginosum 61.9 18.3 (1) 51.1 65.5 99.3 short-term persistentParnassia palustris 39.3 6.2 0.0 - - - short-term persistentPeucedanum palustre 93.0 44.5 - 13.1 32.0 100.0 short-term persistentRhinanthus angustifolius agg. 47.5 28.6 - 7.2 87.0 100.0 short-term persistentThalictrum flavum 84.8 40.6 (1) 19.8 51.7 99.3 short-term persistentTriglochin palustre 92.0 29.4 - 21.0 64.4 100.0 short-term persistentValeriana dioica 48.4 34.8 - 68.4 86.2 100.0 short-term persistent

Carex demissa 58.0 25.5 66.9 8.7 9.7 35.0 long-term persistentCarex echinata 80.0 44.1 95.8 5.0 12.7 38.8 long-term persistentCarex panicea 14.9 83.4 92.6 5.5 20.0 33.6 long-term persistentJuncus filiformis 166.5 230.0 69.3 - - - long-term persistentPedicularis palustris 76.6 93.5 58.3 41.3 56.4 75.0 long-term persistentPotentilla palustris 68.9 23.8 40.2 12.1 21.1 45.2 long-term persistentSilene flos-cuculi 84.8 90.8 72.6 18.7 30.0 50.0 long-term persistentViola palustris 89.8 58.8 80.4 13.7 24.7 53.0 long-term persistent

Germination [%] Mortality [%]

Jensen (2004)




Seed bank analysis 31 wet grasslands in Northern Germany Meso- and eutrophic fen grasslands (Scheuchzerio-Caricetea,

Calthion, Lolio-Potentillion) Managed and abandoned sites

Burial experiments 45 species of the regional fen flora Carex (Schütz 1997, 1998, 1999) Regional rare species (Jensen 2001, 2004) Asteraceae and Lamiaceae (Brändel 2004)

Database and literature survey ‚Thompson-Database‘ (Thompson et al. 1997) 16 seed bank studies (‚wet grasslands‘, 143 sites in Europe)

Database on seed banks of wetland species




described


site


site

Soil layers not subdivided

xxxxxxxxxxxxxxxx


vegetation x

AT LEAST SHORT-TERM PERSISTENT

xxxxxxxxxx PRESENT

xxxxxx


xx

Soil layers subdivided by

depth xxxxxxxx

Present in the seed bank

xxxxxxxxxxx x

Absent from the seed bank xxxxxxxxxxx

x

SHORT-TERM PERSISTENT

xx


xxxxxx


xx


xxxxxx


site


xx

A SPECIES FOUNDx


described

Present only in surface soil

xxxxxxxxx xxxxxxx

More freq. in upper but

present in lower soil layers

At least as freq. in lower

as in upper soil layers


vegetation x


site

Thompson et al. 1997

Criteria

Presence/absence in vegetation and seed bank

Depth distribution in the soilAll COUNTSREAL SEEDBANK COUNTS

Classification rules for seed bank types



Classification of species to seed bank types Indirect procedure following Thompson et al. (1997): All counts, Real

seedbank counts Direct procedure (burial experiments)

Calculation of the Longevity-Index (LI, Bekker et al. 1998)

Silene flos-cuculi

Methods: Seed bank research

transient short-term persistent

long-term-persistent

LI

All counts 34 52 30 0.7Real seedbank counts 6 52 30 0.9Burial experiments 0 2 2 1.0

LI = short-term + long-term persistent records

transient + short-term + long-term persistent records



Seed persistence of species groups

LI All counts Real seedbank counts Burial experiments

0.0

0.2

0.4

0.6

0.8

1.0

Fo

rag

e g

rass

lan

d

Oth

ers

Ru

der

al

Wet

gra

ssla

nd

Ree

d

Fen

Fo

rag

e g

rass

lan

d

Oth

ers

Ru

der

al

Wet

gra

ssla

nd

Ree

d

Fen

Fo

rag

e g

rass

lan

d

Oth

ers

Ru

der

al

Wet

gra

ssla

nd

Ree

d

Fen

aba

ab

b

abab

nsLow habitat specifity

High habitat specifity ab

aab

b ab

ab

Kruskall-Wallis-Test



Habitat specifity, rarity and seed persistence

Low habitat specifity

High habitat specifity

Lo

ng

evit

y -

Ind

ex

0.0

0.2

0.4

0.6

0.8

1.0

***

All counts

Real seedbank

counts

Burial experi-ments

Common

Rare

All counts

Real seedbank

counts

Burial experi-ments

**

Mann-Whitney-U-Test



Summary: Persistence and seed banks

Seed banks of many wet grassland species are at least short-term persistent

Rare or endangered wet grassland species do not have a lower persistence than common species

Seed persistence in the soil has been underestimated by the methods applied by Thompson et al. (1997)

Seed banks can be an important factor for the conservation or restoration of species-rich wet grasslands



Seed transport by running water Seed trapping (Eider: 2 years; Soomaa: 1 summer) Recapture experiment (Eider) Dispersal of seed mimics (Elbe) Modelling of hydrochorous seed transport (Elbe)

Seed sedimentation during flooding Drift-line material (Eider, Soomaa, Elbe)

Astroturf mats (Eider and Elbe: 2002, 2004)

Dispersal by wind and animals Community seed rain (Eider; Jensen 1998) Seed shadow of wet grassland species Seed content of cattle faeces

Methods: Seed dispersal research



Establishment: Methods and questions

Factorial field experiments. Manipulation of …

• Seed availability (e.g. sowing, removal of the seed bank, exclosure of seed dispersal, application of seed-containing drift-line material)

• Microsite availabilty (e.g. creation of gaps, mowing)

Is seedling establishment of wetland species limited by seed or by microsite availability?

Is species richness of wetlands limited by seed or by microsite availability?



Large gaps

Small gaps

Control

Mowing

Sowing experiment (Pedicularis and Rhinanthus)

• 10 blocks per species

• 4 disturbance treatments (control, mowing, small gaps, large gaps)

• 4 sowing densities (control, 250, 1250, 5000 seeds per m²)

• Monitoring of recruitment, survival and reproduction



controlmowing

small gapslarge gaps

Disturbance treatment

2

10

20

40

Nu

mb

er o

f in

div

idu

als

Pedicularis palustris

250 1250 5000

Sowing density[seeds/m²]

July 2002

controlmowing

small gapslarge gaps

Disturbance treatment

2

10

20

40

Rhinanthus angustifolius

Nu

mb

er o

f in

div

idu

als

• bienniel

• Seed weight: 1.1 mg

• Limited by seed and by microsite availability

• annual

• Seed weight: 2.2 mg

• Limited only by seed availabilty



Rasran, Vogt & Jensen (2006)

Field experiment in floodplain grasslands (Soomaa NP, Estonia)

Drift line

Dis

turb

ance

yes no

no

small gaps

large gaps



Effects of seed banks and dispersal on wetlands

Sp

ecie

s n

um

ber

of

recr

uit

ing

se

edli

ng

s p

er 6

25cm

²

0

4

8

12

yes no

16

no small gaps

large gaps

Drift line Disturbance

a

b

c



Wanner (2002)

Effects of seed banks and dispersal on wetlands: Baltic coastal grasslands

Nu

mb

er o

f se

edli

ng

s p

er g

ap

Yes NoSeed Bank

0

5

10

15

20

25

30

35

40

45

50

Yes No

without vegetative regrowth

with vegetative regrowth



Ludewig (2009)

Species not present in the vegetation are in general limited by seed availability (Pedicularis, Rhinanthus)

Species with high seed densities in the seed bank or with high potential of hydrochorous seed dispersal might establish after some kind of soil disturbance

Germination from seed banks might contribute to species richness in wetlands (floodplain grasslands, coastal grasslands)

Summary: Establishment



Summary and conclusion

Many wetland species have persistent seed banks

Hydrochorous dispersal enables wetland species to move large distances and to reach new habitats

Seed banks and seed dispersal can significantly contribute to nature management and restoration of wetlands

Conservation of still existing wetland patches should obtain priority

Restoration success of wetlands depends on: site conditions, management, spatial and temporal aspects



THM

You have only to dig a pond anywhere … and you will soon have … the usual waterplants (Thoreau 1860)

You have only to restore the site conditions and a proper hydrological management anywhere and you will soon have the usual wetland species



PostdocMarkus BrändelAntonia Wanner

Technische MitarbeiterClaudia MählmannJutta KrügerDetlev Böhm

Doktoranden und wiss. MitarbeiterKati VogtLeonid RasranWiebke SchoenbergSonja HeemannSigrid SuchrowGesine EngelsEbrahem MohamedKristin LudewigFrauke MüllerSebastian SchmidtKatharina SchmidtChristian Butzeck

Vielen Dank

AbschlussarbeitenSandra BurmeierAnke BrandtDirk LübsenJessica HenselJan SchwertdfegerMarie HrachNina PohlmannFelix HeydelJessica EhrhardtJessica KlepgenChristian KlausLotte KorrellAgathe SchaddachJule KrauseKatharina KleißFriederike FreiwaldSinaida AlbrechtFrauke BrunckhorstCarolin GallinatJana Melanie HankeCaroline ThiemNina Moniac



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