Labile carbon input alleviates nitrogen‐induced community instability in a meadow steppe

Abstract Global nitrogen (N) deposition continues to threaten plant diversity and ecosystem stability despite a recent slowdown in its increasing rates. Labile carbon (C) may help reduce excess N by alleviating microbial C starvations, but their role in mitigating the harmful effects of N enrichment remains unclear. In a meadow steppe in northern China, we conducted a 9‐year (2014–2022) field experiment with six levels of historical N addition (0, 2, 5, 10, 20, and 50 g N m −2 year −1 , 2014–2019) and three levels of labile C (0, 200, and 2000 g C m −2 year −1 ). Three years after ceasing N treatments (2020–2022), above‐ground net primary productivity (ANPP) remained high under N addition. However, species richness and community stability continued to decline with increasing N addition rates. Labile C addition reduced the dominance of certain plant species within the community while it enhanced species asynchrony and below‐ground net primary productivity (BNPP). Boosted regression tree models indicated that the high levels of labile C inputs improved community stability by enhancing BNPP, which increased the relative importance of BNPP to the community stability from 7.5% to 27.4% as labile C input rose. Synthesis . Our results highlight how labile C inputs can counteract the negative impacts of N enrichment on community stability via enhancing plant‐microbe competition and increasing below‐ground biomass allocation.