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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).