Elevational demographic differences of two alpine cushion plants: Indications of potential divergent responses to climate warming

We integrated field surveys with controlled laboratory and field experiments to investigate population structure along an elevation gradient and drivers of seedling survival and growth in two co-occurring cushion species, Arenaria polytrichoides and A. oreophila.Results: Both species exhibited elevational demographic differentiations, with A. oreophila showing a stronger consistent pattern. Small individual abundance increased with elevation in both species, tough more steeply so in A. oreophila.

Additionally, A. oreophila generally had higher proportions of large individuals at higher elevations. These patterns suggest A. oreophila may be more responsive to elevation-coupled environmental changes and exhibits faster population turnover. Controlled experiments showed that warmer temperatures promoted seedling growth and biomass but reduced survival in both species, with optimal survival at intermediate temperatures (10/15 °C and 15/20 °C); most growth responses, however, did not differ between species.

Bare ground habitat enhanced germination and growth but reduced survival compared with grass- or shrub-covered habitats. The two species showed species-specific responses to microhabitat, especially when interacting with other environmental factors. Experimental warming using open-top chambers alone did not significantly affect seedling growth.

Collectively, these results suggest that divergent population responses to climate change may already be emerging between co-occurring cushion species, but these differences appear to be shaped primarily by species-specific microhabitat use and population structure rather than by intrinsic differences in early life-stage sensitivity.Conclusions: Effective management in rapidly warming mountain regions must therefore account for the interplay between microhabitat heterogeneity and broad-scale climatic drivers.

Long-term monitoring and transplant experiments are required to confirm whether the observed elevational patterns reflect ongoing climate-driven range shifts.