Increased precipitation has stronger effects on plant production of an alpine meadow than does experimental warming in the Northern Tibetan Plateau

The Tibetan Plateau is overall getting warmer and wetter, whereas the relative responses of plant growth to warming and increased precipitation are not fully understood. Therefore, a field warming (control, low- and high-level) and increased precipitation (control, low- and high-level) experiment was conducted to compare the relative effects of warming and increased precipitation on the normalized difference vegetation index (NDVI), soil-adjusted vegetation index (SAVI), aboveground biomass (AGB) and gross primary production (GPP) in an alpine meadow in the Northern Tibetan Plateau since June 2014. The low- and high-level experimental warming significantly decreased soil moisture (SM) by 0.02 m3 m−3 and 0.04 m3 m−3, but significantly increased air temperature (Ta) by 1.91 °C and 3.51 °C, respectively, across the three growing seasons in 2014-2016. The low- and high-level warming did not significantly affect NDVI, SAVI, AGB and GPP across the three growing seasons in 2014-2016. The low- and high-level increased precipitation did not significantly affect Ta, but significantly increased SM by 0.02 m3 m−3 and 0.03 m3 m−3, respectively, across the three growing seasons in 2014-2016. The high-level increased precipitation significantly increased NDVI by 18.7%, SAVI by 18.4%, AGB by 11.4% and GPP by 25.0%, whereas the low-level increased precipitation only tended to increase NDVI by 9.8%, SAVI by 8.2%, AGB by 6.2% and GPP by 12.9%. Therefore, increased precipitation had stronger effects on NDVI, SAVI, AGB and GPP than did experimental warming in this alpine meadow site of the Northern Tibetan Plateau.