Does precipitation affects soil respiration of tropical semiarid grasslands with different plant cover types?

Examination of the effects of altered precipitation and atmospheric temperature patterns on ecosystem processes are an active area of research. Influences of these climate factors may change when plant cover and species composition are disturbed as a consequence of land use change altering ecosystem processes, such as soil respiration. We addressed the following question: how does experimentally manipulated reduction in the size of each precipitation event influence soil respiration fluxes (Rs) in a tropical semiarid grassland with different plant cover and species composition? Rainout shelters were installed over eight yr old planted monospecific plots (4 m2) of Bouteloua gracilis, the keystone species of the grassland biome, and over mixed grassland plots in sites that recovered from abandoned agricultural land, allowing full or a 50% reduction of ambient precipitation. Soil respiration rates as well soil temperature (Tsoil) and soil water content (SWC), as controlling factors, were monitored. Overall, SWC was the most important control for Rs explaining ∼70% of its variability, followed by Tsoil which explained ∼25% and plant cover type having a minor effect (3%) explaining Rs variability. Still, Rs exhibited differential responses when comparing plant cover types; SWC in the mixed grassland had up to 90% relative influence on Rs as compared to 10% by Tsoil. In contrast, Rs rates in monospecific B. gracilis plots exhibited less overall variability considering SWC (55-60%) and Tsoil (40-45%), suggesting that grasslands dominated by the keystone species are more resilient and better buffer the effects of extreme climatic drought conditions on ecosystem processes.