Temperature sensitivities of aboveground net primary production, species and phylogenetic diversity do not increase with increasing elevation in alpine grasslands

Responses of aboveground net primary production (ANPP), species and phylogenetic α- and β-diversity of plant community to a long-term experimental warming are not fully understood in alpine grasslands on the Tibetan Plateau. A long-term warming experiment was deployed at three alpine grassland sites (4313 m, 4513 m, 4693 m) in the Northern Tibet since 2010. The ANPP, plant α- and β-diversity were investigated in 2011–2019. Experimental warming reduced multi-year mean ANPP, aboveground net primary production of sedge and aboveground net primary production of graminoid by 42.53%, 71.18% and 89.59% at elevation 4313 m, aboveground net primary production of forb by 30.23% at elevation 4513 m, and aboveground net primary production of sedge by 27.56% at elevation 4693 m, but increased aboveground net primary production of forb by 33.88% at elevation 4313 m in 2011–2019. Experimental warming reduced multi-year mean species richness by 20.70% and phylogenetic diversity by 14.72% at elevation 4313 m, species richness by 10.31% and phylogenetic diversity by 10.00% at elevation 4693 m in 2011–2019. The temperature sensitivities (the relative change caused by 1 °C increase in air temperature) of ANPP, species and phylogenetic α-diversity decreased with increasing warming duration, but the temperature sensitivity of phylogenetic β-diversity increased with increasing warming duration (p