Crop functional diversity drives multiple ecosystem functions during early agroforestry succession.
Abstract
We still lack practical guidelines for diversifying cropping systems that consider both yield and regulating functions of agroecosystems. Recent studies have suggested that maximizing functional diversity (FD, the distribution of species with different functional traits in the niche space) may lead to agroecosystems with greater multifunctionality due to niche complementarity. Therefore, scientists are now advocating the use of a trait-based approach to develop multifunctional sustainable agroecosystems. In order to assess the effects of crop FD on key agroecosystem functions and to consider trade-offs and synergies among them, we established, in late 2016, permanent experimental field plots of successional agroforestry systems (SAFS), in humid subtropical Southern Brazil. The experiment represents a gradient of plant functional trait diversity (designed FD based on leaf nitrogen concentration), while maintaining crop species richness constant across all treatments. Our hypothesis is that the observed FD of crops (hereafter, crop FD) drives multiple agroecosystem functions. We determined the observed FD by quantifying traits of crops and weeds (maximum plant height, leaf area, specific leaf area) and performed two data collections (March and September 2017) at the end of the summer and winter crops respectively. We used structural equation modelling to test a hypothetical causal model to explain how crop FD affects three functions: weed suppression, soil protection (soil cover by either crops or weeds) and crop yield. Our results support the hypothesis that high crop FD drives agroecosystem processes and contributes to the provision of multiple ecosystem functions. We found that with greater crop FD in SAFS, crop plants occupied a large niche space, thereby increasing the total photosynthetic light intercepted in the agroecosystem, that in turn, increased crop yield. Additionally, greater FD increased soil protection by crops and decreased weed cover. This greater FD also reduced the FD of the weed community.