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RESEARCH PRODUCT

Response of weed species to water stress: quantification and formalisation in a model of crop-weed interactions

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International audience; Reducing herbicide use requires alternative strategies to regulate weeds. In the context of climate change, these alternative strategies must tolerate climatic hazards, among which is water deficit. Simulations models that predict the effects of cropping systems, in interaction with pedoclimate, on crop-weed demography are powerful tools to identify weed management strategies that tolerate climatic hazards. However, due to knowledge gaps, competition for water is rarely included in models of crop-weed demography, which can thus not be used to identify weed management strategies that tolerate water deficit. The present study aimed to quantify the response of weed species to water stress, and to identify mathematical formalisms to introduce competition for water into a crop-weed demography model, i.e. FLORSYS. In a greenhouse experiment, Alopecurus myosuroides, Amaranthus hybridus and Abutilon theophrasti were grown at 4-5 water regimes, ranging from 75 to 20% of the water holding capacity. Plants were grown individually in pots. Three times per day, each pot was automatically weighted and, whenever necessary, watered with a complete nutrient solution (N-P-K) to reach the targeted water regime. Seven weeks after germination, plants were sampled to measure plant growth traits. For the three species, leaf, stem and root biomasses were all affected by water regime. The intensity of the response to water stress differed among species, with A. theophrasti being the most sensitive and A. hybridus the least sensitive species. The higher the leaf area was when water availability was non-limiting, the more it was affected by the water regime. Data analysis (under progress) and literature are used to identify mathematical formalisms accounting for the response of annual crop and weed species to water stress, especially biomass production (photosynthesis) and allocation within the plant (aboveground vs. belowground, leaf vs. stem, reproductive vs. vegetative biomass). The aim is to identify generic equations, i.e. valid for a wide range of annual crop and weed species, each species being characterised by a set of specific parameters. These formalisms will be included in the FLORSYS model which simulates weed dynamics and crop canopy growth in virtual fields over the years with a daily time step. The final aim is to use the completed model to identify sustainable weed management strategies that are robust to climatic hazards.