Drought decreases the positive impact of warming on an alpine grassland community

Temperature and precipitation are the main factors determining plant community succession and aboveground net primary productivity (ANPP) in natural grasslands. However, most climate manipulative experiments have mainly focused on their impacts in isolation, especially in alpine regions. Here we explored the relative effects and interaction of warming and precipitation alteration on succession and ANPP using a 7-year experiment involving warming with precipitation alteration (increase (IP) or decrease (DP) in precipitation relative to ambient precipitation (AP)) on the Tibetan Plateau. Our results showed that warming and warm-wet conditions increased species richness, diversity index, height and cover of overall species. Conversely, decreasing precipitation reduced them, but increased S. purpurea and the rate of change in community composition. Importantly, warming mitigated the impacts of decreased precipitation on plant community composition, and the interactive effects of warming and altered precipitation on cover, height and plant ANPP varied with year and plant species. Generally, warming increased community ANPP through increases in forb ANPP or non-dominant species ANPP and biodiversity regardless of change in precipitation. However, decreased precipitation reduced community ANPP via decreases in the ANPP of sedges and forbs and biodiversity. Precipitation alteration affected the relationship between biodiversity and community ANPP regardless of warming (IP<AP<DP). Therefore, generally warming and decreased precipitation have opposite effects on ANPP in the alpine grassland, suggesting that warming mitigated the negative impacts of drought on the ANPP of the alpine grassland.