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"Root litter decomposition: effects
of species and plant presence“
and my previous research
Sirgi Saar
Advisor: Gerlinde De Deyn
Wageningen, 2014
Introduction
• Decomposition of OM is a key process in ecosystem's
carbon cycle, releasing carbon to the atmosphere.
• Speed of litter decomposition is determined by
climate and litter quality (Zhang et al. 2008)
• Litter is a nutrient source for both plants and soil
microbes.
• Priming effect
Hypotheses
• H1: Presence of living roots can increase
decomposition rate because of priming effect.
• H2: Higher nutrient (N) concentrations induce
faster loss of weight in litterbags.
- N concentration of roots is most important
according to Vivanco et al. (2006)
Treatments
Soil legacy
Litter decomposition
with plant
Tr
Plant: Yes
Conditioned soil: Yes
Litter bags: No
Control: with
unconditioned soil
Plant: Yes
Litter bags: Yes
Control: with empty
litter bag
Litter decomposition
Tr
Plant: No
Litter bags: Yes
Control: with empty
litterbag
Methods
• 7 litter species:
Grasses: Lolium perenne, Arrhenaterum elatius, Festuca rubra,
Legumes: Trifolium repens, Trifolium pratense, Vicia cracca,
Forb: Cichorium intybus
• Root litter from previous experiment of Janna Barel.
• Living roots of Trifolium repens
• 10% unconditioned Clue soil, rest is sterilised.
• 8 weeks of decomposition
Methods
Results
No correlation between decomposition speed and N, P
or K content.
90
chicory
80
Litterloss %
70
60
Legumes
50
40
30
without plant
20
Grasses
10
with plant
0
0.000
0.010
0.020
0.030
N concentration (mg) in mg litter
0.040
0.050
Results
Root litter of different species decomposes with different speed
F plantpresence= 42.2
d.f. = 1,91
P < 0.001
90
without living
plant
with living
plant
80
70
*
Litterlosspercent
60
50
F litterspecies= 434.6
d.f. = 6,91
P < 0.001
*
40
F plantpresence ×
litterspecies= 15.4
d.f. = 6,91
P < 0.001
30
20
10
0
Ciin
forb
Arel
Feru Lope Trpr
grass
Trre
legume
Vicr
Discussion
+ N addition affected leaf and litter traits, but not
decomposition rates (Kazakou 2009).
+ Lignin, dry matter and C content predict decomposition of all
plant organs, N is important in leaves (Freschet 2011).
? Lignin:N ratio as best chemical predictor of litter
decomposability (Aerts 1997).
• Our results are in accordance with preferential substrate utilization
hypothesis (Sparling, 1982): if soil OM degradation requires too
much energy, microorganisms can switch to fresh OM as a C source.
• How to explain slower decomposition rate with
legume, but only for non legume roots? Nutrient
competition between plant and microbes?
Conclusions
• C1: Presence of living roots can decrease
decomposition rate.
• C2: Higher nutrient (N,P,K) concentration
doesn’t cause faster litter decomposition.
Next ->taking carbon into account. Analyses on
plant matter.
References
• Aerts, R. (1997) Climate, leaf litter chemistry and leaf litter decomposition
in terrestrial ecosystems: a triangular relationship. Oikos
• Freschet, G.G.T. et al. (2011) A plant economics spectrum of litter
decomposability. Functional Ecology.
• Kazakou, E. et al. (2009) Litter quality and decomposability of species
from a Mediterranean succession depend on leaf traits but not on
nitrogen supply. Annals of Botany.
• Sparling, G.P. et al.(1982) Effect of barley plants on the decomposition of
14C-labelled soil organic matter. Journal of Soil Science.
• Vivanco, L. et al. (2006) Intrinsic effects of species on leaf litter and root
decomposition: a comparison of temperate grasses from North and South
America. Oecologia
• Zhang, D. et al.(2009) Rates of litter decomposition in terrestrial
ecosystems: global patterns and controlling factors. Journal of Plant
Ecology
Thanks to
• Gerlinde De Deyn
• Janna Barel
• Henk Martens
Plant root exudates mediate neighbour recognition
and trigger complex behavioural changes
Marina Semchenko, Sirgi Saar, Anu Lepik
New Phytologist, 2014
Understanding the mechanisms of
neighbour recognition is important for the
study of:
ecosystem functioning and plant evolution,
nature conservation,
development of techniques to reduce
wasteful competition in agricultural crops.
Introduction
Plant-plant recognition:
• Between kin
(Dudley & File, 2007; Biedrzycki et al., 2010;
Lepik et al., 2012).
• Between species (Krannitz & Caldwell, 1995;
Semchenko et al., 2007).
• Between communities (Mahall & Callaway, 1996)
• Mechanisms: remain largely unknown
(Callaway, 2002; Callaway & Mahall, 2007).
Hypotheses
via root exudates plants can:
H1) Recognise neighbours
H2) Recognise their siblings, distinguish them
from non-relatives and cooperate with them.
H3) make distinction between plants from
different communities and
H4) different species.
Methods
• Exudate collection
with water
• Filter sterilised
exudates
• Control – fertiliser
solution
• 20 times during 10
weeks, 25->55ml
• Real soil
• Focal plant
Deschampsia
caespitosa
Treatments
Focal plant is D.caespitosa from Kärevere
EXUDATE
SPECIES
POPULATION
FOR HYPOTHESES
KIN
Deschampsia
caespitosa
Kärevere
Kärevere
H1, H2
Soomaa
H3, H4
STRANGER/
SAME
POPULATION
OTHER
POPULATION
OTHER SPECIES,
SAME
POPULATION
Lychnis flos-cuculi Kärevere
OTHER SPECIES,
OTHER
POPULATION
CONTROL
-
H1, H2, H3,H4
H3, H4
Soomaa
H3, H4
-
H1
Kin recognition (H1, H2)
F exudate origin = 1.6
d.f. = 1,9
P = 0.2396
F exudate origin × sample
location = 0.3
d.f. = 1,18
P = 0.5815
Root mass (g)
F sample location = 7.1
d.f. = 1,18
P = 0.0155
0.2
0.15
0.1
0.05
0
siblings
unrelated
Kin recognition (H1, H2)
F sample location = 37.4
d.f. = 1,18
P < 0.0001
F exudate origin × sample
location = 0.9
d.f. = 1,18
P = 0.3486
Root length density(cm/cm3)
F exudate origin = 5.4
d.f. = 1,9
P = 0.0445
25
20
15
10
5
0
siblings
unrelated
Kin recognition (H1, H2)
F sample location = 24.1
d.f. = 1,18
P = 0.0001
F exudate origin × sample
location = 0.5
d.f. = 1,18
P = 0.5045
Specific root length(cm/mg)
F exudate origin = 6.6
d.f. = 1,9
P = 0.0305
25
20
15
10
5
0
siblings
unrelated
Population and species-specific effects
(H3, H4)
F community × species =
4.9
d.f. = 1,26
P = 0.0363
F species × sample
location = 6.5
d.f. = 1,35
P = 0.0150
Conclusions
C1) Exudates trigger different spatial responses.
C2) and mediate kin recognition and cooperation.
C3) Plants can recognise conspecifics from their
own population.
• Root proliferation was mainly achieved through
changes in morphology, rather than in biomass -> no
tragedy of commons.
C4) We didn’t find reaction towards other species.
References
Biedrzycki ML, Jilany TA, Dudley SA, Bais HP. 2010. Root exudates mediate kin recognition in
plants. Commun Integr Biol 3(1): 28-35.
Callaway RM. 2002. The detection of neighbors by plants. Trends in Ecology & Evolution 17(3):
104-105.
Callaway RM, Mahall BE. 2007. Plant ecology - Family roots. Nature 448(7150): 145-147.
Dudley SA, File AL. 2007. Kin recognition in an annual plant. Biology Letters 3(4): 435-438.
Krannitz PG, Caldwell MM. 1995. Root growth responses of three Great Basin perennials to
intraspecific and interspecific contact with other roots. Flora 190(2): 161-167.
Lepik A, Abakumova M, Zobel K, Semchenko M. 2012. Kin recognition is density-dependent and
uncommon among temperate grassland plants. Functional Ecology 26(5): 1214-1220.
Mahall BE, Callaway RM. 1996. Effects of regional origin and genotype on intraspecific root
communication in the desert shrub Ambrosia dumosa (Asteraceae). American Journal of Botany
83(1): 93-98.
Semchenko M, John EA, Hutchings MJ. 2007. Effects of physical connection and genetic identity
of neighbouring ramets on root-placement patterns in two clonal species. New Phytologist
176(3): 644-654.
Acknowledgements
Anu Lepik
Marina Semchenko
Research project was
financed by Tartu
University (0119)
and Estonian
Science Foundation
(grant 9332).
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