Climate and tillage system drive weed communities’ functional diversity in a Mediterranean cereal-legume rotation

Abstract

The first step to develop an environmentally sound weed management is to know how weed communities respond to environmental drivers. Among these, climate and management practices are probably the more determinant factors for annual plants community assembly. In this framework, a trait based approach may be useful to assess weed community responses and the processes behind them. Here, we focused on three non-inversion tillage practices which differently affect soil conditions and the vertical distribution of weed seeds. We also took into account the climate variability across years. We specifically asked whether the type of non-inversion tillage system and the annual variability in climatic conditions explain the differences in the functional structure of weed communities. To assess this question we conducted a nine yearlong field experiment in which three non-inversion tillage systems were compared: subsoil tillage, minimum tillage and no-tillage. We characterized the functional structure of weed communities by first obtaining data on three resource acquisition traits (specific leaf area, plant height and growth habit) and five regenerative traits (seed weight, longevity index, dispersal structures, seed cover and emergence time). Then, we computed the community weighted mean (CWM) and the mean pairwise distance (MPD) of each trait as well as a multi trait MPD index. Climate annual conditions were characterized based on autumn-winter precipitation, average temperature and number of frost days. We found that tillage systems and climatic factors mainly sorted weed species according to their emergence time and seed weight. Weed communities from no-tillage plots were characterized by having an earlier emergence and seeds without pericarp. Regarding climatic conditions, we found that warmer and rainier autumn-winter conditions were related to lower functional diversity of regenerative traits and higher diversity in terms of resource acquisition traits. Our results highlight that factors affecting seedling emergence as well as traits related to these processes are critical during weed community assemblage. Our results also showed that none of the compared tillage systems was clearly outstanding in terms of functional diversity, but that each system benefited certain functional design. Furthermore, the relative importance of these management practices to drive weed functional structure was clearly lower than the effects of climatic inter-annual fluctuations.