Plant Traits Diversity and Redundancy Are Drivers of Soil Cover Process in Initial Agroforestry Systems

Literature has pointed to benefits of applying trait-based ecology approach in agricultural research. This approach can be used to assess different aspects of biodiversity related to ecosystem functioning and ecological stability, i.e. functional diversity (FD, diversity of functional traits) and functional redundancy (FR, diversity of species performing similar functions in the ecosystem). The primary objective of this study was to investigate in what extent FD and FR drive the soil cover process by plants in agroforestry systems. Soil cover by plant is a important agroecosystem function that are related to weed suppression process and soil protection. An experiment using three different functional composition of crop plants has been conducted since 2016 in Florianópolis (southern part of Brazil), under agroforestry system management. We used Structural Equation Modeling (SEM) for testing causal models among crop FD, crop FR, weed FD, weed FR and soil cover. Plants abundance and soil cover were visually assessed using 0.5x0.5m quadrats. Seven plant traits were used to determine Rao quadratic entropy index (a measure for FD): maximum plant height, leaf area, leaf nitrogen concentration, specific leaf area, stem specific density, clonality, nitrogen fixing. These traits are related to biogeochemical cycles and competitive ability of plants. FR was determined as the difference between Gini-Simpson index and FD. Our results support the hypothesis that agrobiodiversity insures ecosystem processes and contributes significantly to delivery of ecosystem services. However, we found that FR and FD contribute to agroecosystem in different ways (FIGURE 1). High FD of crops, which means more ecological niches occupied by crop plants, causes increase in soil cover by crops. High FR of crops, which means that the system has insurance crop species for occupying these niches, causes decrease in soil cover by weeds. Additionally, low FR in weed community diminish the soil cover by this plants. Although further investigations are needed to address the influence of FR and FD in multifunctionality of agricultural systems, our results suggest that, agroecosystems should be designed in order to increase biodiversity of plants but maintain the balance between functional diversity and functional redundancy.