Abstract: Against the backdrop of global change, nitrogen deposition and shifting precipitation regimes jointly influence ecosystem functions. Elucidating the regulatory mechanisms of nitrogen-water interactions on productivity sensitivity under varying precipitation intensities is crucial for understanding how grasslands maintain stability under future climate scenarios. We analyzed the effects and mechanisms of nitrogen and water additions, as well as their interactions, on vegetation productivity sensitivity based on a six-year (2017-2022) manipulative experiment in a temperate typical steppe of Inner Mongolia. The experimental design comprised factorial N addition at 10 g N·m^-2·a^-1 and water addition totaling 80 mm·a^-1, with the latter implemented under two precipitation event-size regimes: a low-intensity regime (2 mm per event applied 40 times annually) and a moderate-intensity regime (10 mm per event applied 8 times annually). The results showed that only the combined treatment of low-intensity water addition and N addition significantly enhanced vegetation productivity sensitivity. In contrast, water addition alone (both low and moderate-intensity), N addition alone, and the combination of N addition with moderate-intensity water addition exerted no significant effects on productivity sensitivity. These findings demonstrate that grassland productivity sensitivity is jointly regulated by the synergistic interaction of N and water additions, highlighting the pivotal role of precipitation event size in maintaining ecosystem functioning. Our study provides empirical evidence supporting the maintenance of ecosystem stability under global change.

Key words: nitrogen deposition, precipitation intensity change, productivity sensitivity, stability, ecosystem function