Long-term warming and nitrogen addition interact to reduce population growth and buffering capacity in a desert steppe ecosystem

Abstract Background and Aims Understanding species viability under global change is vital for biodiversity conservation. Climate warming and nitrogen deposition may interactively affect population viability by altering the underlying demographic process (survival, growth, reproduction) across different life stages. Therefore, studies integrating all demographic rates across the life cycle are essential to address the impacts of global change on species viability. However, such studies remain rare. Methods We conduct a 20-year field experiment (2006-2025) in a desert steppe in northern China to assess the effects of climate warming and nitrogen addition on plant population dynamics. Using data collected from 2020 to 2025, we parameterize stochastic integral projection models (IPMs) to quantify the stochastic population growth rate (λs) of two dominant species, Stipa breviflora and Cleistogenes songorica under climate warming and nitrogen addition. Key Results Both warming and nitrogen addition reduce survival in both species, leading to declines in λs. Furthermore, populations under these treatments exhibit amplified fluctuations in vital rates, reduced demographic buffering, and accelerated decline in λs. Notably, the demographic effects of warming and nitrogen addition exhibit antagonism through demographic compensation, rather than simply additive or synergistic. Conclusions and applications Our long-term experiment demonstrates that climate warming and N deposition interactively reduce long-term population viability, indicating an increased risk of species extinction under global change. Moreover, we show that the decline is further exacerbated by temporal variability, highlighting that long-term demographic studies are key for understanding and predicting species viability under global change.