Livestock grazing can strongly determine how grasslands function and their role in carbon cycle. However, how ecosystem carbon exchange responds to grazing and the underlying mechanisms remain unclear. We measured ecosystem carbon fluxes to explore the changes in carbon exchange and their driving mechanisms in a 16-year long term experiment with different grazing intensities in a desert steppe grassland. We found that grazing intensity influenced above- and belowground biomass during the peak growing season, primarily by decreasing shrubs and semi-shrubs and perennial forbs. Furthermore, alter patterns of net ecosystem exchange primarily via their negative influence on the biomass of shrub and semi-shrub. In addition, grazing-induced reduction belowground biomass, as well as in total plant nitrogen and soil ammonium nitrogen, can strongly influence ecosystem carbon exchange and soil respiration. When nitrogen is lost from the soil due to grazing, plants reallocate resources belowground to maintain growth and development, thus promoting photosynthesis and respiration. Our study indicates that soil available nitrogen and shrubs and semi-shrubs are important factors in regulating ecosystem carbon exchange under grazing disturbance in the desert steppe, which provide a basis for grazing management.

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.