Topography and Soil Nitrogen Content in Lakeshores Modulate the Maintenance Pathways of plant Community Stability

Environmental change-induced biodiversity loss highlights the need to understand how environmental heterogeneity regulates ecosystem stability. However, the maintenance mechanisms of plant community stability in lakeshore habitats remain unclear. Using trait-based surveys across 26 lakeshore sites combined with multi-group path analysis, we quantified how plant species diversity, functional diversity, and functional redundancy jointly determine community within-site spatial stability across soil nitrogen (N) and height relative to water surface (HRWS) gradients. Results indicate that the mechanisms regulating plant community stability are highly context-dependent. The drivers of stability quantified using ICV (inverse coefficient of variation) varied with nutrient availability: under low N conditions, higher species and functional diversity were positively associated with higher ICV, consistent with classic ecological expectations. However, in high N environments, this relationship inverted, with higher species diversity paradoxically leading to lower stability, suggesting a shift to a competition-driven regime. Furthermore, the expression of these mechanisms depended on the HRWS gradient, with a trade-off between the complementarity effect of species diversity and the insurance effect of functional redundancy emerging only in middle HRWS zones. This study provides valuable insights into the intrinsic, context-dependent mechanisms underlying the spatial stability of plant communities in lake riparian areas and is expected to inform the management and conservation of plant communities in freshwater lakes worldwide.