Cover crops may influence soil ecosystem functioning. However, little is known about the role of below-ground root architectural traits in coupling cover plant diversity with soil ecosystem properties. We hypothesize that cover plant species richness may enhance the expression of root traits, and thus could influence plant diversity effects on essential indicators of soil physicochemical heterogeneity, such as the composition of soil aggregate-size classes and nutrients, and soil organic matter (SOM) and carbon (SOC) contents. To test this hypothesis, we studied the impact of a cover plant species richness gradient (1, 3, 6 species per community) on plant and soil properties in the deep-pot (35.5cm) experiments. Our experiment included 11 monoculture- and mixture cover plant treatments in triplicate (33). At reproductive maturity, we collected soil and plant samples. The four-soil aggregate-size classes, such as large macro- (>2000μ), small macro- (<2000-500μ), meso- (<500-250 μ), and micro-aggregates (<250 μ) were separated by the dry sieving. Root traits such as surface area (cm2) and length (cm) were determined by the Winrhizo. The soil nutrient, SOM, and SOC contents were determined by standard methods. We used Loreau and Hector's (2001) method for partitioning the net biodiversity effect on plant productivity and soil properties.
Results/Conclusions
The cover plant species richness increased the total productivity, and the expression of below-ground root architectural traits, such as surface area (cm2) and length (cm). It also enhanced the composition of soil aggregate-size classes and nutrients, and the contents of SOM and SOC across the soil depth. While, plant diversity increased and decreased the relative abundance of meso- and micro-aggregates respectively, though it did not affect large macro- and small macro-aggregates. The root architectural traits positively correlated with the composition of soil aggregate-size classes and nutrients, and the contents of SOM and SOC. Considering significant correlations of soil aggregate-size classes with plant and soil nutrients, our results suggest that, similar to biological diversity, the diversity in soil abiotic components could also be important for the provision of soil ecosystem services. Based on mathematically partitioning the plant diversity effects on soil properties, we conclude that competition among roots in species-rich than poor communities may improve soil physicochemical heterogeneity. To our knowledge, this is the first report to study soil-plant interactions at root-trait and soil aggregate-size level, while our findings contribute to pre-existing knowledge on root traits and their role in influencing plant diversity effects on soil ecosystems.