Decreasing elevational gradient in peak photosynthesis timing on the Tibetan Plateau

The Tibetan Plateau has experienced elevation-dependent climate warming, which has profoundly influenced the seasonal dynamics of plant growth. However, how peak photosynthesis timing (DOYPmax), a key component of plant growth seasonality, responds to climate change on the Tibetan Plateau remains unclear. Here, we investigated the change in the elevational gradient in DOYPmax on the Tibetan Plateau during 2001-2018 and its drivers. We mapped the primary climatic constraint on plant photosynthesis and found that it was temperature at 3000-4000 m a.s.l. in the central and eastern parts but soil water at 4000-5000 m a.s.l. in the southwestern part. DOYPmax increased by 1.0 & PLUSMN; 0.1 days/100 m with increasing elevation from 3000 to 5000 m a.s.l., but the elevational gradient in DOYPmax decreased by -0.8 & PLUSMN; 0.2 days/100 m/decade during 2001-2018 due to both direct and indirect effects of climate change. Specifically, at 3000-4000 m a.s.l., DOYPmax was delayed because of the direct effect of the increase in soil water. At 4000-5000 m a.s.l., DOYPmax advanced due to the warminginduced earlier green-up date in the central plateau and the drought-induced later spring phenology in the southwestern plateau. Such a change in plant growth seasonality should alter seasonal carbon cycle of alpine ecosystems, summer diets of the migrant herbivores and alpine plant-animal interactions along elevation gradients, but further efforts are needed to clarify how herbivores that migrate long distances, e.g., Tibetan antelope, adapt to changes in the elevational gradient in peak plant growth timing.