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Litter decomposition in forest ecosystems: assessing the functional role of climate, litter quality and soil organisms

Final Report Summary - DECOMFORECO (Litter decomposition in forest ecosystems: assessing the functional role of climate, litter quality and soil organisms)

In our project, we investigated the influence of climate, soil organisms and plant litter quality on litter decomposition in forest ecosystems at different spatial and temporal scales. Contrary to most previous investigations, this project focused primarily on the effects of functional diversity at three trophic levels (primary producers, decomposers and detritivores), rather than on taxonomic diversity, in order to bridge aboveground and belowground diversity with litter decomposition. An important goal of this research project was to elucidate the relative importance of biotic vs. abiotic controls on litter decomposition. We used a suite of approaches, from latitudinal gradients to climate manipulations, disciplines (microbiology, biogeochemistry, plant functional ecology, and community ecology), ecosystems (terrestrial - forests and aquatic - forest streams), and spatial scales (continental, regional and local) to provide a novel mechanistic understanding of patterns governing litter decomposition.

In the Continental Scale Objective, we analyzed a biome-wide climatic gradient spanning from the tropics to the subarctic and replicated experimental design in aquatic and terrestrial forest ecosystems. The influence of decomposers, litter traits and biome on litter decomposition was compared between terrestrial and aquatic ecosystems at the continental scale and for individual biomes. In the Regional Scale Objective, we selected ten sites across a mediterranean-temperate climatic gradient in southern France to i) examine the consequences of climate change, litter functional diversity and soil organisms (microbes, microfauna and macrofauna) for litter decomposition, and ii) assess how changes in litter chemistry and decomposers control litter decay at different decomposition stages. In the Local Scale Objective, a combined field and laboratory approach was conducted to disentangle the effects of soil microbes and litter quality on both leaf and root litter decomposition responses to experimental drought.

Our results show that litter micronutrients and environmental variation among biomes were the major drivers of litter C loss in both aquatic and terrestrial ecosystems, but decomposer organisms also played a prominent role in streams. Within biomes, we observed consistent effects of litter micronutrients and stoichiometry on litter C and N loss in forest floors and streams, but not of decomposer complexity. Our results can contribute to improve coupled terrestrial-aquatic ecosystem C models, and may be used to predict how C and N dynamics are impacted by climate change. At the regional scale, the temporal dynamics experiment showed that the implications of litter polyphenols and decomposer organisms temporal dynamics varied along the decomposition process, suggesting that these dynamics should be incorporated for an accurate prediction of litter decomposition. The second regional experiment showed that although climate and litter quality explained most of the variance in litter C dynamics, macrofauna also played an important role. The results of the field-laboratory experiment showed that the decreased soil microbial biomass and altered microbial physiological profiles with reduced rainfall promoted lower fine root ‒ but not leaf ‒ litter decomposition, indicating contrasting mechanisms driving indirect effects of drought on above- and belowground litter decomposition. The understanding of these mechanisms, and the quantification of their relative contribution regarding the direct soil moisture-effects, is critical for an accurate integration of litter decomposition into ecosystem C dynamics in Mediterranean ecosystems under climate change.

Adaptive management of ecosystems should be incorporated into the agenda of policy makers and land managers (both public and private) if we want to be successful under the current scenario of climate change. For doing so, we need accurate predictions of climate change effects on ecosystems, and the identification of the abiotic and biotic factors mediating such effects. Current carbon cycle models, which are fundamental to better understand and predict important ecosystem services such as carbon sequestration and climate mitigation, are limited by robust experimental support for the parametrization of recent advances on litter decomposition. Our project provides such experimental evidence to help incorporate the relative importance of litter decomposition drivers at different spatial and temporal scales, and across terrestrial and aquatic ecosystems, into predictions of climate change effects on the carbon cycle.
Contact details:

Host institution
Centre d’Ecologie Fonctionnelle et Evolutive (CEFE) in Montpellier, France (Centre National de la Recherche Scientifique, CNRS)

Scientist in charge
Dr. Stephan Hättenschwiler
Bioflux Team
CNRS Languedoc-Roussillon, 1919, route de Mende, 34293 Montpellier, France
stephan.hattenschwiler@cefe.cnrs.fr

Researcher
Dr. Pablo García-Palacios
Bioflux Team
CNRS Languedoc-Roussillon, 1919, route de Mende, 34293 Montpellier, France
pablo.garcia@cefe.cnrs.fr
pablogpom@yahoo.es

Project website: https://www.sites.google.com/site/pablogarciapalacios1/home/Marie-Curie-Project