Cet article presente des resultats recents de mesures de protoxyde d’azote realisees sur deux legumineuses : le pois proteagineux d’hiver et le trefle blanc en association de graminees prairiales. Le pois, en comparaison avec d’autres grandes cultures dans des conditions pedo-climatiques identiques, est a l’origine de tres faibles emissions de N2O, aussi bien pendant son cycle cultural que pendant les mois qui suivent sa recolte. Les emissions mesurees sur prairies comportant du trefle blanc sont similaires, quel que soit le taux de presence du trefle dans la prairie, de 35% ou 19%, soit 6,6 et 3,2% de la matiere seche recoltee. Les emissions semblent davantage liees aux apports d’azote realises, bien que provenant majoritairement du pool d’azote du sol. En GC, a l’echelle d’exploitations « type », l’introduction des legumineuses a un effet benefique sur les bilans d’energie non renouvelable (ENR) et de changement climatique (CC) ; qu’elles soient cultivees en culture pure ou en association avec une cereale. En systeme prairial, les bilans se montrent legerement positifs entre systemes intensifs (35% de mais) et systemes extensif (peu de mais et plus d’herbe avec legumineuses) vis-a-vis de l’impact sur le CC. Un gain appreciable (27%) est obtenu vis-a-vis du bilan d’ENR, au profit des systemes extensifs.

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The role of the 4p1000 initiative in defining research priorities for soil organic carbon under the sustainable development agenda

Cornélia Rumpel Farshad Amiraslani Claire Chenu Maira Alejandra Moreno Garcia Cardenas Benoît Henry

Soil carbon

Carbon fibers

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An international inter-comparison and benchmarking of crop and pasture models simulating GHG emissions and removals at field scale

HAL (Le Centre pour la Communication Scientifique Directe) (2014)

Fiona Ehrhardt Jean‐François Soussana Gianni Bellocchi Arti Bhatia Lorenzo Brilli

Benchmarking

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Multi-metric evaluation of an ensemble of biogeochemical models for the estimation of organic carbon content in long-term bare fallow soils

HAL (Le Centre pour la Communication Scientifique Directe) (2019)

Gianni Bellocchi Roberta Farina Fiona Ehrhardt Claire Chenu Jean‐François Soussana

As part of benchmarking actions at international level (FACCE-JPI project CN-MIP), the C-MIP action was initiated in 2016 to address the question of whether ensemble modelling could bring some improvement to the simulation of soil organic carbon (SOC) dynamics. A multi-model ensemble with 25 process‐based integrated C-N models was implemented to compare simulations (before and after model calibration) to SOC data from a network of six long-term bare fallow experimental sites (one site with two options) in Europe. To evaluate single models and the model ensemble, multiple evaluation metrics were aggregated into a single modular indicator, not only accounting for the agreement between model estimates and actual data but also taking into account their structural complexity. Illustrative results of simulated against observed SOC dynamics while also discussing the potential of the multi-metric aggregated indicator to help identifying areas where structural changes in models may be needed to better represent such dynamics.

Biogeochemical Cycle

Soil carbon

Carbon fibers

Content (measure theory)

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Four years of experimental climate change modifies the microbial drivers of N₂O fluxes in an upland grassland ecosystem

Global Change Biology (2012)

Amélie Cantarel Juliette Bloor Thomas Pommier Nadine Guillaumaud Caroline Moirot

Abstract Emissions of the trace gas nitrous oxide ( N 2 O ) play an important role for the greenhouse effect and stratospheric ozone depletion, but the impacts of climate change on N 2 O fluxes and the underlying microbial drivers remain unclear. The aim of this study was to determine the effects of sustained climate change on field N 2 O fluxes and associated microbial enzymatic activities, microbial population abundance and community diversity in an extensively managed, upland grassland. We recorded N 2 O fluxes, nitrification and denitrification, microbial population size involved in these processes and community structure of nitrite reducers ( nir K) in a grassland exposed for 4 years to elevated atmospheric CO 2 (+200 ppm), elevated temperature (+3.5 °C) and reduction of summer precipitations (−20%) as part of a long‐term, multifactor climate change experiment. Our results showed that both warming and simultaneous application of warming, summer drought and elevated CO 2 had a positive effect on N 2 O fluxes, nitrification, N 2 O release by denitrification and the population size of N 2 O reducers and NH 4 oxidizers. In situ N 2 O fluxes showed a stronger correlation with microbial population size under warmed conditions compared with the control site. Specific lineages of nir K denitrifier communities responded significantly to temperature. In addition, nir K community composition showed significant changes in response to drought. Path analysis explained more than 85% of in situ N 2 O fluxes variance by soil temperature, denitrification activity and specific denitrifying lineages. Overall, our study underlines that climate‐induced changes in grassland N 2 O emissions reflect climate‐induced changes in microbial community structure, which in turn modify microbial processes.

Nitrous oxide

Nitrogen Cycle

10.1111/j.1365-2486.2012.02692.x

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La défoliation sélective est le moteur de l'hétérogénéisation d'une parcelle de dactyle sous-exploitée par des brebis

HAL (Le Centre pour la Communication Scientifique Directe) (2001)

Florence Garcia-Launay Pascal Carrère Jean‐François Soussana René Baumont

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