Degradation rather than warming delays onset of reproductive phenology of annual Chenopodium glaucum on the Tibetan Plateau

With degradation and desertification of alpine meadows due to climate warming and overgrazing, the distribution of annual plant species has greatly expanded on the Tibetan Plateau. Most phenological studies in the past decades have mainly focused on perennial plants, and few have studied the phenology of annual plants, despite their different life history. Lack of knowledge regarding how phenological sequences of annual plants respond to climatic warming in degraded areas limits our ability to restore and protect degraded alpine ecosystems under future warming. To study the independent and interactive effects of degradation and warming on the phenological sequences of the annual plant, Chenopodium glaucum, we conducted a two-factor control experiment (degradation: moderate and severe degradation; warming: non-warming and open-top chamber warming) on the Tibetan Plateau during 2014–2016. Our results indicated that out of six phenophases of the annual plant warming only delayed first fruit setting. However, degradation delayed the onset of reproductive phenology of the annual plant, which may cause by decreased soil nutrient, above-ground biomass and richness led by degradation. Furthermore, the independent and interactive effects of degradation and warming on phenological events showed significant interannual variation. Given the vital role of C. glaucum on colonizing desertified ground and promoting vegetation restoration, these mechanisms may be essential for the persistence of the species in the highly degraded alpine meadows on the Tibetan Plateau.