RESEARCH PROJECTS
It is now well known that the soils play central roles in the functioning of the terrestrial ecosystems. They harbor a great biodiversity, 25% of the worldwide species richness. Soils are the physical support of our crops and constructions, they provide nutrients for plants, filter and clean water, etc. Yet they have never been so threatened by human activities. Pollution, urbanization, erosion, loss of biodiversity etc. are all factors that affect the functioning of the soils. It becomes urgent to better understand and describe the soil functioning and its biodiversity (before we can do it anymore...) to fuel innovative ecological intensification pathways.
MULTIPLE BIOTIC INTERACTIONS IN SOIL
How different soil species can affect together plant functions? In the UnlockP project (coordinated by C. Plassard INRA), we conduct several laboratory experiments with the biological model Bacillus subtilis + Rhabditis + Hebeloma cylindrosporum + Pinus pinaster to better understand how mutualist richness improve plant P nutrition from a recalcitrant P source: the phytate.

HUMUS FORMS AND N CYCLE
Project VILFLORHUM coordinated by M. Aubert (ECODIV, GIP ECOFOR). Humus forms are the mirror of the soil functioning. The aims of this project is to improve our knowledge on (i) the relationships between humus morphology and N mineralization, (ii) N cycle and its regulation within the different humus layers and (iii) the environmental factors responsible for the development of humus forms and controlling soil N pathways along forest development. We showed that net ammonification increases with stand age in the organic horizons, whereas both net nitrification decrease in OL and A horizons. Net nitrification takes mainly place in the OF and OH horizons with ammonification always higher in the organic horizons. The fungal N transformations clearly dominate in the OL horizon while bacterial processes appear to be mainly localized in the A horizon. In general, it appears that the intensity of the first steps of the cycle (i.e. N input and ammonification) are favored during the maturation of pure stands of beech while the latter process of the cycle decrease along the chronosequence. We observed several significant correlations between morphological variables and net nitrification or nitrate content within the organic horizons. Some morphological variables, such as the thickness of OF, density of earthworm casts, the structure of the A horizon or the percentage of bleached leaves, were found to be good predictors of in situ mineral N production.

IN SITU EFFECT OF BACTERIAL-FEEDING NEMATODES ON PLANT FUNCTIONS
Free-living nematodes play key role in agriculture. They provide up to 30% of plant N and P and strongly enhance plant growth as well as yield. How to measure their beneficial activities, and not only their abundance, in the field (or at least under field conditions)? Usually, only nematode abundance is investigate, not their activities. In the project INDICE (coordinated by J. Trap, Agropolis Fondation), we developed an original intact soil core technique to assess the mutualistic activity of a Acrobeloides sp. (a bacterial-feeder) and of a whole nematode community on plant nutrition and growth. This technique helped us to identify the agro-ecological practices that optimize the mutualistic activity of nematodes.

P FLOWS FROM SOIL TO PLANT AFTER NEMATODE INOCULATION
Despite significant advances in soil ecology, it is still unclear how soil organisms affect soil P flows in tropical soils. In this project (BAC-RIP, coordinated by J. Trap, CNRS EC2CO), we used radio-active isotopic P in a high P-sorbing acidic soil to better understand how bacterivorous nematodes affect P transfer from soil to plant (rice). This is a major issue since P is the main nutrient-limiting factor in old tropical soils. Increasing plant-available P using ecological intensification is (probably) the only way to ensure sustanaible productive agriculture.

EARTHWORMS AND PLANT DISEASES
Rice cropping faces many constraints. Among them, blast diseases are common, especially the pyriculariosis. How to fight these fungal pests? The usual way is to use tolerant rice cultivars. Here, we explore a new way: the use of earthworms, a natural resource. Using a greenhouse experiment where we can control fungal spore density on rice leaves, we manipulate the presence and abundance of earthworm and silicium. The first results showed a positive effect of combining earthworms and silicium on plant growth while limiting blast disease development. This was not the case with chemical fertilizer that strongly enhanced the fungal pest. A new agro-ecological practice in perspective?

LITTER DECOMPOSITION
Litter decomposition is a key function of terrestrial ecosystems permitting carbon and nutrient cycling. Many soil organisms are involved in litter decomposition. Does deforestation affect the litter decomposition rate? Is related to loss of soil biodiversity due to slash-and-burn technique? A 12-months field experiment has been conduct in Andasibe (Madagascar). Results are not yet available...but soon.

AGROECOLOGY IN MADAGASCAR
In the SECURE project (Agropolis Fondation), Cammisole (FRB) and EcoAfrica (African Union), we aim at developing innovative agro-ecological practices improving soil function restoration using complex organo-mineral matter assemblages. Besides plant yield, we monitor soil carbon and nutrient storage, water cycle, nutrient cycle, biological activities and other soil parameters. All this work is done conjointly with farmers, ecologists, agronomists, genetists, Agrisud International and socio-economics.
