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Seed-earthworm relationships:

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Julia Clause

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Transcript of Seed-earthworm relationships:

Thesis committee
Seed-earthworm relationships:
seed selection and the responses of plant communities

September 4th 2014

Julia CLAUSE

Université de Rouen

Pr. Nico Eisenhauer, Univ. of Leipzig, Germany
Pr. Juan José Jiménez, IPE-CSIC, Spain
Dr. Elise Buisson, Univ. d'Avignon, France
Dr. Paul Kardol, SLU Umeå, Sweden
Pr. Thibaud Decaëns, Univ. de Rouen, France
Pr. Sébastien Barot, IRD Paris, France
Dr. Estelle Forey, Univ. de Rouen, France
Acknowledgments
Estelle Forey and Sébastien Barot
the ECODIV Lab
Estelle Langlois, Pierre Margerie, Matthieu Chauvat, Fabrice Bureau, Michaël Aubert, Thibaud Decaëns, Philippe Delporte, Marthe Akpe-Vinceslas, Ana Ferreira

Chokri, Audrey, Mickaël, Benoit, Gabriel, Ludovic, Sékou

All interns
My family and friends
Collaborators
Christopher J. Lortie, Adam M. Lambert, Don Canestro and the D'Antonio Lab (US), Charlotte Seal (UK)
Symbionts
Root-feeders
AM fungi
N-fixers
Decomposers
Nutrients
Engineers
Soil structure
Earthworms, Ants, Termites
Predators
>6000 earthworm species
Almost all terrestrial ecosystems
Life span in field: 1.25 yrs to 5 yrs (differs with species)
Soil moisture
Temperature (10°C-15°C)
Soil pH (>4)
Amount and quality of food (litter, SOM, live plants, seeds)
dfgdfg

Ingestion and dispersal

Soil seed banks

Seed dormancy germination and establishment

Research objectives
H1: Earthworm specific seed selection alters seed survival and seedling emergence.

 
H2: Seed-earthworm interactions impact the soil seed bank and drive plant community dynamics in semi-natural grasslands.
Asshoff et al. 2010; Bouché 1977, Darwin 1881, Eisenhauer et al. 2011, Grant 1983, Lee 1985
Epigeic
E. fetida
S. mammalis

Endogeic
Ap. caliginosa
All. chlorotica

Anecic
L. terrestris

Baskin and Baskin 2001; Bekker et al. 1998; Moles and Westoby 2004, 2006

Large variety of seeds (or diaspore)

Traits vary between and within species

Morphological and chemical traits

Functions for seed development
Seeds and seed traits
Palatability

Seed traits (round, small...)
Morphology > Chemistry (birds)


Earthworms


actively select seeds
prefer small, round seeds
Do earthworm preferentially select seeds?

Does seed selection depend on specific seed physical or chemical characteristics?

Does ingestion affect seed performance?

MAIN QUESTIONS
Ingestion (%)
Digestion (%)

Clause et al. 2011 Pedobiologia
Digestion (%)
Do earthworms preferentially select seeds?
Does seed selection depend on seed characteristics?
Increased germination

Ingestion: Seed mass and coat thickness reduction
increased permeability


Earthworms

Selectively increased germination by breaking seed dormancy
(grinding, enzymatic activity, growth-hormone)
Eisenhauer et al. 2009a; McRill and Sagar 1973; Nogales et al. 2005; Traveset et al. 2008
Soil seed banks

Pool of viable seeds in the soil


Drivers of plant-plant competition impact on plant communities

Combined
direct
+
indirect
impacts
Seed selection (small, round persistent seed bank)
Seed vertical transportation (predation, germination,...)
Modification of soil properties plant-soil feedbacks
Grime and Thompson 1979;

Thompson et al. 1993, 1997
Eisenhauer and Scheu 2008; Eisenhauer et al. 2007;

Forey et al. 2011
- review;
Laossi et al. 2010; Milcu et al. 2006
Microcosm - Petri dish
Ingestion (%)

 

Seed degradation
Does ingestion affect seed performances?
Seed selection
Preferences varied with earthworm species
L. terrestris
had a more heterogeneous selection
Earthworms preferred small and oil-rich
or protein-rich seeds

Ingestion
reduced germination for small-seeded grasses and legumes
increased germination of herb species

Seed alteration
only some seed species altered
not linked with germination patterns
Key points
MAIN QUESTIONS
Cast properties
Key points
Germination
MAIN QUESTIONS
Key points
Aboveground-belowground
feedbacks

Earthworms - Generalities
Focus on earthworms and seeds
Significant
earthworm-plant
interactions in lab studies...
but what about
earthworm-plant community
interactions?
Introduction
Part I
Seed selection

Part II
Seeds and casts

Part III
Plant communities

Conclusions
& Perspectives

Earthworm
ecological groups

Link studies on seed banks and vegetation science to studies on soil biodiversity
Earthworm cast and middens
Indirect
impact of earthworms on plants growth... but what about
direct
impacts?
Three main ecological groups
Do seeds that survive digestion present specific traits?
Does seed transportation depend on seed traits?
Nutrient-rich environment

Modification of soil physical, chemical, biological properties
Nutrient-rich casts


Selective impact on plant performances and seed production

Plant species impacted by soil properties and earthworm species
Effect on nutrient acquisition vs. nutrient conservation (grasses vs. clover)
Eisenhauer et al. 2009a; Fuji et al. 2012; Puga-Freitas et al. 2012
Asshoff et al. 2010; Doube et al. 1997; Jouquet et al. 2008; Laossi et al. 2010a, b; Scheu 2003
Earthworms and seed selection
What traits attract earthworms the most?
Are all earthworm species attracted to similar traits?
What are consequences for plant species and communities?
Earthworms, seed ingestion and dispersal
Endozoochory

Seed traits determine resistance to digestion
Seed damages
grinding in gizzard
enzymatic activities in gut




Presence in faeces or casts
Selective vertical seed transportation (grass and non-legumes > legumes)
Dìaz 1996; Eisenhauer et al. 2009a,b; Milcu et al. 2006; Piearce et al. 2009; Renier et al. 2008; Traveset et al. 2007
Decaëns et al. 2003; Traveset et al. 2007; Zaller and Saxler 2007; Willems and Huisjmans 1994

Earthworms and seed germination
Does gut passage cause specific seed damage?
Are effects on germination earthworm-specific and seed-specific?
Earthworms and seedling establishment
What impact of cast properties and earthworm species
on seedling establishment?
Earthworms and plant communities
How important is seed upward/downward transportation?
What are the impacts of seed ingestion on the composition and dynamics of plant communities?
Can the earthworm-seed interactions be scaled up to a tool for grassland restoration?
PART I - SEED SELECTION AND INGESTION
PART II - SEEDS IN EARTHWORM CASTS
PART III - EARTHWORMS AND PLANT COMMUNITIES
DISCUSSION
PERSPECTIVES
Seed damage
Lumbricus terrestris
(anecic)
Allolobophora chlorotica
(endogeic)

S. mammalis
(epigeic)
23 seed species
Mixing physical and chemical traits
Ingestion (%)

Clause et al. 2011 Pedobiologia
Effect of ingestion on degradation
What impact of being in earthworm casts?
Clause et al. 2013 Appl. Soil Ecol.
3 earthworm species
3 soil
types
Cast production
Chemical
(C,N,K,P,pH,...)
Physical
(moisture, permeability)
Biological
(bacteria, fungi)
Seedling performance
Dry cast material
Artificial aggregates/casts
+ distilled water
+ control
= 12 treatments
x 5 replicates
=> 60 pots
Inoculation
1 single seed
5 seed species
60 pots
x 5 seed sp. x 3 replicates
=> 900 pellets
Seed germination
Seedling growth

(shoot, root, total
size and biomass)
Monitored for 6 months
Are seed and seedling performances altered in earthworm casts?
Do cast properties change with earthworm species and soil types?
Do seedling performances change with cast properties?
Do cast properties change
with earthworm species and soil types?
Do seedling performances change with cast properties?
Do earthworms increase seedling emergence and species richness from ingesting and transporting seeds?


Do earthworms alter grassland plant composition?


Can earthworms be used as tools for restoration?
3 experiments in 3 different contexts
Chalk grasslands
of Upper-Normandy
Coastal grassland
of central California
Secondary succession and plant community dynamics
Plant- and earthworm-invaded grassland
Grassland in a former gravel-pit
Grassland restoration project
Chalk grasslands
of Upper-Normandy
Coastal grassland
of central California
Do earthworms increase seedling emergence and species richness from ingesting and transporting seeds?
Do earthworms alter grassland plant composition?
Do earthworms alter grassland plant composition?
Native vs. exotic seed species
+ earthworm sampling
+ soil properties
Earthworm population and soil properties
Principal
Component Analysis
(PCA)
And
Seedling composition: similar patterns between sample types (veg ≠ casts, soil)

Positive feedback loop between exotic plant - exotic earthworms
Indirect impact > Direct impact
O
T
E
W
Related thesis papers
Clause et al. 2011 Pedobiologia
1 paper in preparation
1 paper with data in acquisition
Rubia fructicosa
by squirrel
(Traveset et al. 2007)
Rubia fructicosa
by squirrel
(Traveset et al. 2007)
Related thesis papers
Clause et al. 2013 Appl. Soil Ecolo.
1 paper in preparation
Related thesis papers
Clause et al.
submitted in
J. Veg. Sci.
Clause et al.
submitted in
Acta Oecol.
1 paper in preparation
Large,
heavy,
linear
low oil
Species richness
Seedling density
Secondary succession
Secondary succession
Species richness
Seedling density
Native
Exotic
Sample
types
distance-based Redundancy Analysis (db-RDA)
Native
Exotic
Earthworms concentrate seeds in their casts
observed via increased density and species richness of emerging seedlings


Direct impact of earthworms in the field is overpowered
by micro-environmental conditions (light/nutrient competition)




Potential use of earthworms as restoration tools
possible with additional management (chalk grasslands)

15 physicochemical variables
Principal Component Analysis (PCA)
Clause et al. 2013 Appl. Soil Ecol.
LT:
L. terrestris
AC:
A. chlorotica
AR:
A. rosea
C: Control
Axis 1: 43.1%
Axis 2: 22.1%
Properties difference explained by soil (61.8%) >> EW (10.5%)
Histosol:
nutrient-rich
vs. Luvisol:
nutrient-poor
Do cast properties change
with earthworm species and soil types?
Clause et al. 2013 Appl. Soil Ecol.
Seed species effect

Germination higher in nutrient-poor samples (C-Luvisol)
Seedling growth in Control > in casts of endogeic species
Cast properties vary with earthworm species and soil types


Soil types is a more important factor than earthworm species



Seedling growth is not positively impacted
by cast properties
by being in casts

...caused by microbiological properties?
Small, oval
smooth, oil-rich
Most palatable seed species
G. tinctoria
Eisenhauer et al. 2009a
1 cm
1 cm
1 cm
460 dishes
Gr.
Herb (non-leg)
Leg.
Gr.
Herb (non-leg)
Leg.
Multiple Correspondence Analysis (MCA)
Axis 1: 29.6% (size, shape)
Axis 2: 21.4% (weight, oil)
(9.9%)
(3.3%)
Total germination (cumulated percentages)
C: Control
LT:
L. terrestris
AC:
A. chlorotica
AR:
A. rosea
Moisture
NH4+
If > 0: Increasing effect compared to Control soil
If = 0: no effect
If < 0: Decreasing effect compared to Control soil
Does seed ingestion by earthworms benefit seeds?
Seed ingestion and seed digestion is earthworm specific
Correlated to earthworm species
Not correlated to earthworm traits

Earthworm gain weight with some seed species and mostly for
L. terrestris

How does seed selection compare to litter selection?
Patterns of seed-specific seed germination in lab
Mostly decreased germination (digestion, damage)
BUT increased germination and establishment when excreted
AND higher emergence in casts than in soil (
in situ
)
Casts = regeneration niche?
High density and species richness from field samples
BUT increased nutrient content ≠ increased germination and establishment (in lab experiment)

effect on seedling long-term performance? seed protection within casts?
confirm
confirm
confirm and new
confirm
confirm and new
new
new
new
confirm and new
new and unlike previous
new and unlike previous
confirm
new
new
Lab studies ≠ field studies
Fine scale: need to link with
in situ
functions

Examples:
Long-term experiment
in situ
(chalk grasslands)
- earthworms and cast removal
- monitoring of aboveground plant composition

Link seed traits with results from the larger scale experiment


Seed studies need precision
Germination method
only viable seeds
large amounts of soil (=> sieving)


Manual seed sorting
what seeds are we loking for?
highly time-consuming

Barcoding
possibilities to distinguish ingested seed species?
Further impact of seed ingestion on seedlings?
Growth monitoring
after seed ingestion and germination
over several generations of ingested seeds


Earthworms as seed gatherers and seedling predators
do they ingest seeds to promote the seed germination of palatable seedlings?
Does seed ingestion by earthworms benefit earthworms?
Additional findings
Lab results ≠ results
in situ
(grasses vs herbs)

Large quantities of ingested soil --> large quantity of ingested seeds
Potential drivers of plant communities
Accelerate secondary succession

... BUT limiting environmental factors that limit earthworm impact
Can we talk about mutualism or co-evolution?
At first: thought of co-evolution (trait selection)
BUT
generalist feeding behavior (esp.
L. terrestris
)
no clear advantage for seeds or earthworms
No clear pattern when all cycle considered
Seed trait and transportation
Preliminary results
Ingestion (%)
Ingestion (%)
Ingestion (%)
= digestion
Seed size - LT only (length > width)
Seed mass - LT digestion
= digestion
> digestion
Other traits
Full transcript