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

Abstract

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 < 0.05). The temperature sensitivities of both species and phylogenetic β-diversity decreased linearly with increasing elevation (p < 0.05). However, the temperature sensitivities of ANPP, species and phylogenetic α-diversity were not significantly correlated with increasing elevation. Therefore, warming may cause the degradation of Tibetan alpine grasslands through reducing aboveground net primary production and plant α-diversity, especially under the long-term warming conditions. Moreover, it was not always the higher the elevation, the greater the temperature sensitivity of aboveground net primary production, species and phylogenetic diversity.