Contrasting responses of flowering phenology in C₃ and C₄ plants shape grassland community structure under global...

Climate change is known to affect plant phenology. Yet, the sensitivity of flowering phenology in dryland regions to climate change, and the potential implications for community composition, remain largely unexplored. Here, we used an 18-year field experiment to investigate the effects of climate warming and nitrogen addition on flowering phenology of four C₃ plant species and two C₄ plant species, and the cascading effects on the relative abundance of C₃ and C₄ plants in a desert steppe. Across the past 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, respectively. Warming also reduced the duration of flowering by 1.8 ± 0.1 days for C₃ plants but had no effect on C₄ plants, and decreased the dominance of C₃ plants compared to C₄ plants. Nitrogen addition extended the duration of flowering of C₄ plants by 3.4 ± 0.2 days and increased their relative dominance, while decreasing the dominance of C₃ plants. Structural equation models revealed that these phenological responses were largely driven by soil temperature and soil water availability. Our results demonstrate that the different phenological responses of C₃ and C₄ plants contribute to shifts in dominance between these plant types in temperate dryland ecosystems under global changes.