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Assessing climate change impacts on sorghum and millet yields in the Sudanian and Sahelian savannas of West Africa B Sultan, P Roudier, P Quirion et al.Potential forcing of CO2, technology and climate changes in maize (Zea mays) and bean(Phaseolus vulgaris) yield in southeast Brazil L C Costa, F Justino, L J C Oliveira et al. Abstract Over the next few decades, it is expected that increasing fossil fuel prices will lead to a proliferation of energy crop cultivation initiatives. The environmental sustainability of these activities is thus a pressing issue-particularly when they take place in vulnerable regions, such as West Africa. In more general terms, the effect of increased CO 2 concentrations and higher temperatures on biomass production and evapotranspiration affects the evolution of the global hydrological and carbon cycles. Investigating these processes for a C4 crop, such as sugarcane, thus provides an opportunity both to extend our understanding of the impact of climate change, and to assess our capacity to model the underpinning processes. This paper applies a process-based crop model to sugarcane in Ghana (where cultivation is planned), and the São Paulo region of Brazil (which has a well-established sugarcane industry). We show that, in the Daka River region of Ghana, provided there is sufficient irrigation, it is possible to generate approximately 75% of the yield achieved in the São Paulo region. In the final part of the study, the production of sugarcane under an idealized temperature increase climate change scenario is explored. It is shown that doubling CO 2 mitigates the degree of water stress associated with a 4 • C increase in temperature.

Considered as one of the most available radionuclide in soil-plant system, 36 Cl is of potential concern for long-term management of radioactive wastes, due to its high mobility and its long half-life. To evaluate the risk of dispersion and accumulation of 36 Cl in the biosphere as a consequence of a potential contamination, there is a need for an appropriate understanding of the chlorine cycling dynamics in the ecosystems. To date, a small number of studies have investigated the chlorine transfer in the ecosystem including the transformation of chloride to organic chlorine but, to our knowledge, none have modelled this cycle. In this study, a model involving inorganic as well as organic pools in soils has been developed and parameterised to describe the biogeochemical fate of chlorine in a pine forest. The model has been evaluated for stable chlorine by performing a range of sensitivity analyses and by comparing the simulated to the observed values. Finally a range of contamination scenarios, which di↵er in terms of external supply, exposure time and source, have been simulated to estimate the possible accumulation of 36 Cl within the di↵erent compartments of the coniferous stand. The sensitivity study supports the relevancy of the model and its compartments and has highlighted the chlorine transfers a↵ecting the most the residence time of chlorine in the stand. Compared to observations, the model simulates realistic values for the chlorine content within the di↵erent forest compartments.

Vegetation diversity and interaction is thought to have a beneficial effect on ecosystem functioning, particularly improving ecosystem resistance to drought. This is of significant importance in the context of a warmer world, as extreme events such as droughts become more likely. Most of the studies performed so far on vegetation interaction are based on observations. Here we use the land surface model JULES to study the potential of vegetation mixing to mitigate the negative effect of drought events on the land surface through interaction, a mechanism which is difficult to study in situ at large scales. Using a set of simulations with mixed and unmixed vegetation, we show that the carbon, water, and energy fluxes are significantly affected by vegetation competition for water resources. The interaction is in general beneficial for the ecosystem carbon assimilation due to a better use of water resources. This benefit is highest when traits between vegetation types concerning resource competition overlap least. For a tree‐grass combination, mixing improves carbon assimilation by 5% to 8% during summer. The benefit of mixing increases further under progressively more resource‐limited conditions up to an inflection point with a benefit of 14%, after which it falls back to zero under extremely dry conditions. Mixing also tends to reduce the interannual variability of the ecosystem carbon sink and therefore improves the resistance of the ecosystem. Our results highlight the importance of vegetation interaction in climate simulations and impact studies and the potential of vegetation mixing as a mitigation tool.