PROJECT EC2CO-INSU- BIOHEFECT

 

Title

Does litter mixity effect on decomposition depends on the climatic conditions ?

Project Coordinator

Virginie Baldy - virginie.baldy (at) imbe.fr

  

EC2CO project entitled “Does litter mixity effect on decomposition depends on the climatic conditions?” was funded for two years (2011-2013) by the national program EC2CO from the CNRS. Three research units are involved: IMBE UMR 7263, GES INRA UR1119, EcoLab UMR 5245, OHP UMS OSU Pytheas.


Mediterranean ecosystems, is also one of the 34 biodiversity hot spots identified at the global level, are submitted to an old and high anthropogenic pressure directly with one of the highest rates of population growth in Europe and major touristic activities, and indirectly by climate change, with decrease of rainfall and increase of summer temperatures. The Mediterranean region has been proposed for many years as a suitable model region to study drought on biodiversity and ecosystem functionning
The objective of this project is to measure the consequences of an increased drought period on a keyprocess linking biodiversity and function: litter decomposition.

                                                                                                   
We propose to study how climatic context affects mixture of plant species interactions during the decomposition process. The question is whether the change in rainfall directly influences the production and litter decomposition but also indirectly by varying the biochemical quality of the litter, especially secondary metabolites produced by plants (in terms of quality and quantity). Moreover, the study of the mixture of plant species with different chemical features can tell us about the effects of changes in species distribution due to climate change and thus the type of litter coming to the soil.
To investigate the relative importance of both types of factors that influence the decomposition process (i.e. water stress vs biochemical composition of the litter), we study the decomposition of several plant species present on the site and with different chemical signatures. Three species are naturally present in the experimental site, the two tree species Quercus pubescens L. and Acer monspessulanum L., as well as the dominant species of the understorey, Cotinus coggygria Scop. We propose to add to mixture the litter of Pinus halepensis Mill., to test in a functional point of view the possible change of the species assemblage due to climate change.

 

Q. pubescens and A. monspessulanum are known to produce essentially phenolic coumpounds, C. coggygria produces terpenoids and phenolics, particularly large amount of flavonoids and P. halepensis is able to produce amazing amount and diversity of phenolics and terpenoids.

 

We conducted a preliminary experiment consisting in the decomposition of the four plant species cited above, without water stress, in order to increase our knowledge on forest ecosystems and plant species, especially the rate of litter decomposition depending on the litter chemical signature. One of the results showed that litter mixity affects breakdown efficiency (Figure 1): i) A. monspessulanum had a positive effect on decomposition of all others species in two species mixture, ii) P. halepensis decomposition rate was always higher in mixture with all others species compared to monospecific mixture and this rate increased with the species number in mixture, iii) Q. pubescens and P. halepensis showed opposite effects, as Q. pubescens favoured P. halepensis decomposition whereas P. halepensis slowed down Q. pubescens decompositon.

 

 litter decomposition, mixture effects

Fig 1: Relative Interaction Index (RII) measuring decomposition rate of a species i in monospecific mixture relative to its decomposition rates in mixture with species j (means ± SE; n=4). Asterisks indicate significant differences from 0 (t-test, p<0.05). A = Acer monspessulanum, C = Cotinus coggygria, P = Pinus halepensis and Q = Quercus pubescens.

   To complete this study in situ, we performed ecotoxicological tests in the laboratory to assess the potential allelopathic effect of secondary metabolites which can be released during the litter decomposition on a target mesofauna species Folsomia candida (Collembola).

Fig. 2 : Relative survival rate (A), mean mortality (B) and relative reproduction rate (C) of F. candida, in % compared to control watered with water, for the three concentrations of litter water extracts (0, 2.5, 5 et 10%) and the 5 modalities of plant species mixture (A=Acer, C=Cotinus, P=Pinus, Q=Quercus).