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Relative importance of region, seasonality and weed management practices effects on the functional structure of weed communities in French vineyards

Winegrowers have diversified their weed management practices over the last two decades changing the structure and the composition of weed communities. Complementary to taxonomic studies, trait-based approaches are promising ways for a better understanding of weed communities’ responses to environmental and agronomic filters. In the present study, the impact of climate, soil characteristics, seasons and weed management practices (chemical weeding, tillage and mowing) were assessed on weed communities in three French wine-growing regions (Champagne, Languedoc and Rhône valley). These agro-environmental gradients structuring weed communities according to their combination of traits were highlighted using multivariate analysis (RLQ). The impacts of these filters on Community Weighted Means (CWM) and the Community Weighted Variance (CWV) of weed communities were analysed using mixed and null modelling. Our results showed that spatio-temporal and weed management practices variables explained from 13% to 48% of the total variance of CWM (specific leaf area, maximum height, seed mass, flowering onset and duration and lateral spread). Region, seasonality and management practices explained 53%, 28% and 19% of CWM marginal variance, respectively. Weed management impacted CWM and CWV through two main gradients: (i) a soil disturbance gradient with high mechanical disturbance of soil in tilled plots and low mechanical disturbance in chemically weeded plots and (ii) a vegetation cover gradient with high vegetation abundance in mowed plots compared to more bare soils in tilled and chemically weeded plots. Chemically weeded communities showed trait values of ruderal strategies (low seed mass, small-stature) in Languedoc. Mowed plots were associated with more competitive strategies (higher seed mass, higher stature and lower SLA) in Languedoc. Tillage favoured communities with high seed mass that increases the viability of buried seeds and high lateral spread values associated to the ability to resprout after tillage in Languedoc and Champagne. This study demonstrated that trait-based approach can be successfully applied to perennial cropping systems such as vineyards, in order to understand community assembly to better guide weed management practices.