Inconsistent changes of biomass and species richness along a precipitation gradient in temperate steppe

Biomass and species richness are two important indicators of ecosystem stability. The relationship between biomass and species richness along precipitation gradient in semi-arid regions is significant for prediction of ecosystem stability under the estimated climatic drying in the future. In this study, we investigated species richness, aboveground biomass and cover of temperate steppe along a mean annual precipitation (MAP) gradient in central Inner Mongolian of China. We also measured water use efficiency (WUE) of selected species and overall communities. Our results showed that biomass almost remained unchanged in the moist half of the gradient, but species richness decreased markedly with decreasing MAP. Species richness further showed a negligible decrease, whereas a much sharper drop was detected in biomass towards the arid end with decreasing MAP. Vegetation cover shared a similar pattern with biomass and dropped sharply towards the arid end, which may create a strong light and low competition environment favoring C4 plants. The increment of C4 species richness could prevent a more intensive decline of species richness under severe arid conditions by raising overall community water use efficiency. Thus, plant communities experiencing water deficiency could also maintain species richness with the occurrence of C4 plants.