Increased precipitation weakens the role of <i>Stipa breviflora</i> as the keystone species in a desert steppe

Abstract Precipitation significantly influences the composition and structure of grassland ecosystems, particularly in arid desert steppes. Stipa breviflora, as a keystone species, plays a crucial role in maintaining the stability of the desert steppe. However, the response of Stipa breviflora's succession strategy to changes in precipitation within the community remains uncertain. Since 2016, this research was conducted in a desert steppe in Inner Mongolia, China, involving control precipitation (PCK), and increases of 50% (P50) and 100% (P100) in natural precipitation. We measured biomass, height, and canopy cover, calculated the importance value (IV) by species, and assessed the photosynthetic parameters and leaf elemental content of Stipa breviflora in 2021 and 2022. Results showed that the increase of precipitation significantly reduced the IV of Stipa breviflora. The net photosynthetic rate, transpiration rate, stomatal conductance, aboveground biomass carbon (AGBC) content and aboveground biomass nitrogen (AGBN) of Stipa breviflora leaves grew considerably in experimental plots receiving more precipitation, while δ13C value of leaves decreased significantly. Linear regression analysis and structural equation model show that although the increase of precipitation improved the adaptability of Stipa breviflora functional traits and increased its IV, a higher transpiration rate significantly contributed to the decrease in its IV. Consequently, our research reveals the succession strategy of Stipa breviflora and provides a theoretical basis for studying the response mechanisms of desert steppe plant communities to climate change.