Global change, including atmospheric nitrogen (N) deposition, shifts in precipitation patterns, and anthropogenic activities such as mowing, have great impacts on the structure and functions of grassland ecosystems. However, whether and how the N deposition, change in precipitation and long-term mowing influence the stability of above- and below-ground net primary productivity of grassland ecosystems remain unexplored.

Here, we investigated the effects of N addition and water addition on the stability of above-ground net primary productivity (ANPP) and below-ground net primary productivity (BNPP), and explored the driving factors in a 19-year water addition and N addition experiment under the long-term-mowing and no-mowing regimes in a temperate steppe in Inner Mongolia.

Long-term mowing weakened the positive effect of water addition on ANPP stability by dampening the effect of water addition on species asynchrony, and altered the effect of N addition on ANPP stability from neutral to negative by exacerbating the negative impact of N addition on species asynchrony. By contrast, long-term mowing enhanced the positive effects of water addition and N addition on BNPP stability by strengthening the effects of water addition and N addition on grass ANPP, which subsequently decreased the standard deviation (SD) of BNPP. Under the long-term-mowing regime, water addition directly enhanced ANPP stability, whereas N addition reduced ANPP stability by decreasing species asynchrony. Water addition and N addition enhanced grass ANPP, thereby leading to a decrease in the SD of BNPP and consequently an increase in BNPP stability. Under the no-mowing regime, water addition directly enhanced ANPP stability and indirectly increased ANPP stability by increasing species asynchrony. Water addition promoted species asynchrony, leading to a reduction in the SD of BNPP and an increase in BNPP stability, while N addition increased BNPP stability via enhancing grass ANPP.

Our results reveal that the responses of grassland ANPP and BNPP stability to water addition and N addition depend upon long-term-mowing management. These findings highlight the necessity to take into account the grassland management regimes in evaluating ecosystem stability under the scenario of global change.