Impact of climate change and agricultural management on soil CO2 emissions: from microscale investigations to large-scale predictions – MICROLARGE

The project will evaluate the impact of more frequent and more intense drought events on CO2 emissions of temperate soils and how such relationships are modulated by the legacy of agricultural management practices. The project will propose an upscaling methodology to improve prediction of large scale models of soil organic matter decomposition. It will be based on the elucidation of the key mecanisms taking place at the microscopic scale of the soil microbial habitats. We will submit small soil cores sampled under different soils and agricultural managements to wetting/drying cycles with different durations of drought as well as frequencies and number of wetting/drying cycles until mimicking semi-arid climate. The project will test the main hypotheses explaining flushes of CO2 emissions on rewetting, which are the release of microbial products created during the cycles (extra-cellular enzymes, osmolytes, dead microbial cells) and modification of soil architecture responsible of the release of soil organic matter that was previously physically protected from microorganisms. To do so, the project will: i) combine an unprecedented set of multi-scale and multi-temporal data imaging tools describing soil microhabitats (from µm to cm scale) and ii) produce ambitious and novel 3D microscale models of soil organic decomposition simulating for the first time the dynamics of soil architecture, water, microbial diversity and activity. The mechanistic knowledge gained from microscale investigations will be transferred to the land surface ORCHIDEE model by including new emerging statistical functions emulating the microscale models. The new version of ORCHIDEE will be evaluated against soil respiration continental database.