Asymmetric impacts of daytime and nighttime warming on vegetation coverage in marsh wetlands of the Tibetan Plateau

Climate change profoundly affects vegetation coverage in marsh wetlands of the Tibetan Plateau, thereby influencing regional biodiversity. Until recently, understanding of how vegetation coverage in Plateau marshes respond to climatic changes is limited. In this study, spatiotemporal change in vegetation coverage across the Tibetan Plateau was analyzed using leaf area index and meteorological data from 2001 to 2022, with emphasis on hydrothermal forcing mechanisms. Growing season average vegetation coverage increased significantly (P < 0.05) by 0.01 m2 m–2 a–1. While overall growing season precipitation show no significant influence on vegetation coverage across the plateau, changes in monthly precipitation were found to have region-specific effects. Specifically, increased precipitation in May and June significantly reduced vegetation coverage in the central plateau but enhanced it markedly in the southwestern region. Regarding temperature effects, growing season warming generally increased vegetation coverage across the plateau. We identified an asymmetric effect of diurnal temperature on vegetation coverage: nighttime warming had a more pronounced positive effect than equivalent daytime warming. A 1 °C increase in growing season daytime maximum and nighttime minimum temperatures increased vegetation coverage by 0.15 and 0.21 m2 m–2, respectively. This asymmetry effect was also evident across specific months. Nighttime warming in May and September significantly enhanced vegetation coverage across the plateau, whereas daytime warming during these months showed no significant effect. Contrastingly, increased daytime and nighttime temperatures in July were associated with decreased and increased vegetation coverage, respectively, in the southwestern region. Our findings will contribute to further understand the relationship between global climate change and alpine wetland ecosystem.