Functional shifts in weed community composition following adoption of conservation agriculture

International audience; To better understand the changes in weed communities following the adoption of conservation agriculture (CA), we investigated the functional composition of weed communities in fields implementing CA continuously from 1 to 21 years. Weed surveys were conducted in 100 winter wheat fields of 53 farmers in the Bourgogne-Franche-Comte region, Eastern France. Ten response traits were selected to highlight changes in the functional composition of weed communities, using weighted mean value for quantitative traits and an approach based on composition analysis for qualitative traits. Out of the 10 traits, four were impacted by the time following the adoption of CA significantly, whereas two only showed trends. Specific leaf area, leaf dry matter content, seed dispersal mode and soil seedbank longevity did not change over time following adoption of CA, whereas changes were observed for plant type, Raunki AE r's life forms, Ellenberg's indicator value for light and, germination and flowering periods. Phanerophyte and geophyte life forms, summer-germinating species and spring- and summer-flowering species increased with time following adoption of CA. Shade-tolerant species, not present in fields recently converted to CA, established later. Community-weighted mean of seed mass and the percentage of graminoids tended to increase with time following adoption of CA. Some functional shifts in weed communities occurred quicker than others (i.e., summer-germinating species increased after at least 10 years of continuous application of CA principles). These results can be used to inform farmers moving towards CA about expected changes.