Does nitrogen deposition affect plant community stability–area relationships? The role of biodiversity, area, and seasonal N addition

Nitrogen (N) deposition generally reduces the temporal stability of plant community (community stability) across spatial scales. Theory predicts that community stability increases with sampling area, leading to a positive community stability–area relationship (CSAR). However, because atmospheric N deposition exhibits a temporal pattern, little is known about how the responses of community stability differ under seasonal N deposition, or whether seasonal N deposition alters the CSAR and its underlying mechanisms. Understanding this is crucial for assessing multi-scale ecological sustainability under global change. We conducted an experiment with N input during autumn, winter, or the growing season in a temperate grassland. Based on six years of survey data across nested spatial scales ranging from 0.01 to 16 m², we explored the potential impacts of seasonal N enrichment on the CSAR. Our results showed that community stability increased with sampling area, regardless of N addition. Each of the three seasonal N inputs caused a significant reduction in the CSAR intercept, while N addition in winter or the growing season also reduced the CSAR slope. Biodiversity had a stronger effect than area in maintaining the positive CSAR, and mediated the relationship between area and stability. High biodiversity preserved community stability by maintaining population stability and compensatory dynamics. By validating and extending the CSAR theory under seasonal N input, our research showed that N input in winter or the growing season caused a greater reduction in plant community stability at larger spatial scales. As global N deposition continues to increase, small-scale studies may undervalue the adverse impact of N input on stability, while large-scale studies based only on N input during the growing season may overestimate this effect. These findings highlight the need to consider both spatial scales and seasonality of N deposition for accurately predicting ecosystem responses to atmospheric N deposition.