Global climate change has had a profound impact on the ecology of arid regions, specifically on vascular plants and biological soil crusts (biocrusts). However, the responses of these organisms to changes in rainfall patterns remain poorly understood. To address this gap, we conducted a 4-year field experiment in the Loess Plateau, where we reduced rainfall levels to different extents (-75%, -50%, -25%, 0%). Our results revealed divergent response patterns between biocrusts and grasses to altered rainfall amounts. Biocrusts showed a threshold response to rainfall reduction, with a tipping point between -25% and -50%. The effects of rainfall reduction also varied depending on the specific year of the experiment. In addition, rainfall frequency was found to be the primary factor determining the response of biocrusts to altered rainfall, with biocrust cover significantly and positively correlating with increasing rainfall frequency. On the other hand, grasses were more directly influenced by rainfall amount than by soil water availability, which was in turn mediated by biocrusts at depths of 5 and 10 cm below the soil surface. Soil water availability became negligible over time, especially for deeper soil layers (10, 20, 40 cm below the surface). Cumulative effects of reduced rainfall also had strong impacts on grass cover. Overall, our study highlights the coordinated but distinct responses of biocrusts and vascular plants to changes in rainfall patterns, emphasizing the need for a comprehensive understanding of dryland ecosystems. These findings could inform efforts to mitigate global climate change and combat desertification in arid regions.

biocrust,dryland,climate change,ecohydrology,desertification