Synergistic constraints of warming temperatures, intense UV-B radiation, and increased seed burial depth on the recruitment of alpine cushion plants

This study investigated how warming temperatures, intense UV-B radiation, and increased seed burial depth affect the emergence, growth, and mortality of seedlings from eleven cushion plant species in the alpine subnival zones of the Himalaya-Hengduan Mountains in southwestern China. Results revealed that deep seed burial (exceeding 1 cm) significantly suppressed seedling emergence of cushion species, with substantial viability loss occurring within three months for seeds buried at greater depths. Warmed temperatures accelerated emergence rates, enhanced seedling growth but resulted in high seedling mortality rates. In addition, intensified UV-B radiation consistently impaired seedling recruitment across multiple stages, leading to reduced emergence percentages, stunted growth, and increased mortality rates. These findings suggest that the coarse, mobile substrates characteristic of subnival zones exacerbate natural constraints on seedling emergence for cushion plants. While increased temperatures may promote emergence and growth, they can also result in significant mortality, thereby hindering future population recruitment and expansion. Furthermore, enhanced UV-B radiation due to ozone layer depletion poses additional threats to cushion populations. Nevertheless, the observed species-specific responses to these factors indicate diverse population dynamics among cushion species under future climate change scenarios. This study provides essential insights into the potential trajectories of alpine cushion populations under climate change, offering valuable implications for the conservation of ecosystems and biodiversity.