Changes in plant and arthropod functional traits mediate land use and precipitation effects on grassland production

Much effort has been devoted to better understanding the effects of land-use and climate changes on biodiversity and ecosystem functions (BEF); however, the mechanistic pathways behind the observed changes remain largely unexplored, especially for grassland arthropod community. Using a 7-year grassland experiment in Inner Mon-golian steppe, we examined the relative importance of direct versus indirect (through mediating plant and arthropod biodiversity) effects of four land-use types (growing-season grazing, spring & summer grazing, mowing and enclosure) and precipitation variation in two climatically contrasting years on plant and arthropod productivity. Our results showed that: (1) the variation patterns of species and functional diversity and pro-ductivity across land use types were significantly different between plant and arthropod communities, though both plants and arthropods had their community-weighted mean size (i.e., plant height and arthropod body size) decreased under grazing or mowing; (2) moderate grazing and plant growing-season precipitation enhanced plant productivity mainly via indirectly increasing plant functional dispersion and decreasing plant nitrogen concentration associated with the shift in dominant species, but reduced arthropod productivity majorly by direct grazing damage and less importantly by indirect mediation of arthropod body size; (3) grassland man-agement and precipitation-induced variations in plant and arthropod productivity could be well explained by the changes in their functional traits and diversity, but not species richness. Our results indicate the importance of trait-based method in understanding the mechanisms of management and precipitation affecting plant and arthropod productivity, and suggest that biological traits in multiple trophic groups can be used as efficient indicators in the assessment of grassland ecosystem health.