[en] The general objective of this project was to contribute to the evaluation of land use and management impacts on C sequestration and nitrogen dynamics in soils. The land used through the presence/absence of crops and their species, and the land management through tillage, localisation of crop residues, fertilizer applications,... are important factors that affect the dynamics of organic matters in soils, particularly the mineralization of C and N, the losses to the atmosphere and hydrosphere, the retention of carbon into the soil. This project was conducted by four research groups, three of them having expertise in nutrient cycling of three major agro-ecosystems (arable crops, grasslands, forests) and the fourth one having expertise in modelling long term effects of land use on C storage into the soils. Within this common project one major objective was to better understand the fate of plant litter entering the soil either as above litter or as root litter. The focus was put on two factors that particularly affect decomposition: the initial biochemical quality of plant litter, and the location of the decomposing litter. One innovative aspect of the project was the use of stable isotope as ¹³C for carbon, based on the use of enriched or depleted ¹³C material, the only option to assess the dynamics of 'new' C entering the soil on the short term, in order to reveal the effects of decomposition factors. Another aspect was the simultaneous study of C and N. The project consisted in experiments relevant for each agro-ecosystem, in forest, grassland and arable soils for which interactions between residue quality and nitrogen availability on the one hand, residue quality and location on the other hand, was investigated. A common experiment was set up to investigate the potential degradability of the various residue used (beech leaf rape straw, young rye, Lolium and dactylic roots) in a their original soils and in a single soil was assessed. Based on these experiments, the Roth-C model of Coleman and Jenkinson (1996) was used to simulate the short term evolution of residual C, biomass C. A new parametrization based on biochemical composition of residues was proposed. (authors)

[en] Global environmental and climate conditions fluctuate on all kind of spatio-temporal scales. Some fluctuations or change/trends are not only anthropogenic, but have different regional and national signatures. While the frequency of extreme events on smaller scales is changing, the public sector and general opinion become more and more aware and concerned of local impacts from global environmental and climate changes. Indeed, negative effects and feedbacks, might occur on ecosystems, natural resources, buildings and grounds, superstructures, economies, food security, public health. This is how, during 1999, a concerted French initiative led to the research program 'Management and Impacts of Climate Change' (GICC). GICC is essentially managed by the Ministry of Ecology and Sustainable Development in close collaboration with the Inter-Ministerial Mission on Greenhouse Effect (MIES). GICC started in 1999. Its first phase (1999-2006) included four calls for proposal (1999, 2000, 2001, and 2002). In parallel and in 2003-2004, the MIES has been developing the so-called 'Climate Plan' based upon three principles : Insure that France follows agreements from the 'Kyoto Protocol'; Participate in ways and means leading to reduction of greenhouse gases by 75% in 2050; Allow for reduction of pollution from transportation means. Input from GICC Phase One final reports are contributing to 'Climate Plan'. The eight themes proposed by GICC-1 (1999-2002) are as follows: Theme 1: Evolution scenarios of the average and extreme features of the 21. Century climate; Theme 2: Interactions between climate, economy and society; related timescales; Theme 3: Role of carbon forest uptake and agricultural practices on climate policies; Theme 4: Links between national and international activities; Theme 5: Towards new inventories of GHG and aerosols (direct and indirect) emissions; Theme 6: Impacts on terrestrial biosphere; Theme 7: Impacts on hydro-systems; Theme 8: Impacts on public health. A symposium presenting the available results of the GICC first phase has taken place in MEDD, Paris, November 23-24, 2004. A final presentation workshop of the first phase took place in Paris, on May 11-12, 2006. This document is the proceedings of this scientific restitution seminar. It is organized in 9 sessions which follow the 8 themes listed above plus a round table for the status and perspectives of the GICC program. (J.S.)