The plant microbiome significantly influences plant health and ecosystem functions, yet its response to environmental change and links to plant diversity are not fully understood. We investigated the impacts of climate warming and nitrogen deposition on leaf epiphytic and endophytic bacterial communities in Stipa breviflora and Cleistogenes songorica over an 18-year field experiment in temperate desert steppe. Results showed increased diversity in both leaf bacterial types, with epiphytic biomass rising and endophytic biomass falling due to distinct mechanisms. Epiphytic diversity and biomass increased with leaf temperature and transpiration rate, endophyte diversity increased with leaf carbon and nitrogen concentrations, and endophytic biomass related to leaf nitrogen and phosphorus levels. Structural equation modeling revealed both epiphytic and endophytic bacterial diversity correlated with reduced plant diversity, which in turn was linked to increased leaf bacterial diversity, indicating a complex response of phyllosphere bacteria to global changes in perennial grassland ecosystems.

The strong control of temperature on the timing of plant phenology is expected to cause substantial shifts in flowering times under climate change. Yet, the sensitivity of flowering phenology in dryland regions to climate change, and the potential implications for community composition, remain largely unexplored. Here, we investigate the effects of climate warming and nitrogen addition on flowering phenology of four C3 plants and two C4 plants and explore cascading effects on shifts in C3 vs C4 plant dominance in a 17-year field experiment in a desert steppe. Across the last 10 years of the experiment (2013–2022), we found that warming had a greater effect on phenological shifts in C3 than in C4 plants. Warming significantly advanced the flowering time of C3 plants by 4.3 ± 0.1 days and of C4 plants by 2.8 ± 0.1 days. Warming also reduced the duration of flowering by 1.8 ± 0.1 days and decreased the dominance of C3 plants compared to C4 plants (P＜0.05). Nitrogen addition extended the duration of flowering of C4 plants by 3.4 ± 0.2 days and increased their relative dominance, while having no effect on C3 plants. Structural equation models highlighted that these phenological responses were influenced by soil temperature and soil water availability. Our results show the divergent phenological responses between C3 and C4 plants under global changes, predicting shifts in dominance between these plant types in temperate dryland ecosystems.