Figure 3. Effects of aridity on the relationships between plant species richness and ecosystem functioning. Relationships between plant species richness and aboveground biomass (a) and SOC (b), and effects of plant species richness on ecosystem functions (c, the slope of the relationships between plant species richness and aboveground biomass and SOC) along aridity gradients. * P ≤0.05,** P ≤0.01, ***P≤0.001.