Simulate Potential Effects of Climatic Changes on the Soil

Future changes in the climate and the composition of the atmosphere will be shown in the evolution of thermal and rainfall regimes, vegetation and land uses, all factors which have an effect on the soil and its dynamics. The soil is at the interface between the lithosphere, the atmosphere, the hydrosphere and the life which it supports. In addition, because of its organic matter, it contains a major part of the biosphere's carbon (Robert, 2000). Any modification in soil agricultural practices or ground cover vegetation may therefore have consequences for the global carbon cycle via their impact on the dynamics of soil organic matter. Conversely, changes in the composition of the atmosphere may bring about changes in certain soil characteristics, particularly the organic reserve (C, N), nutritive elements and acidity, conditions of oxidoreduction, soil water and physical characteristics.

Numerous questions remain unanswered and would benefit from research campaigns. How will the organic reserves in the soil develop and at which rate? Will the soil behave like a sink or an additional source of CO2 (particularly under the effect of the increase in respiration) and what, in return, will be the effect on the composition of the atmosphere? Changes in soil use will also be important. They themselves put a question mark over ecosystems in a transitory state. Will there be synergic or antagonistic effects between changes of usage (which are determined largely by economic factors) and climatic changes, will there be any effects in return? In this respect, the example of rice is very illuminating: if, as we have seen, climatic change has effects on world rice production and its distribution (Horie et al., 2000), the production of rice on the planet may itself have a significant effect on climatic change, particularly through the emission of methane from flooded paddy fields (Reicosky et al., 2000). The hydrologic cycle, the properties of the soil, and the way crops are grown could significantly alter the fluxes of methane produced, mechanisms of which it is important to be aware.

To answer all of these questions, an understanding of the functioning of the current ecosystems is necessary. But facing the transitory nature of the expected impact, only modelling will be able to provide information on the simultaneous consequences of changing agrosystem and ecosystem management practices.

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