Field-based observations of regional-scale, temporal variation in net primary production in Tibetan alpine grasslands

Net primary production (NPP) is a fundamental process of natural ecosystems. Temporal variation of NPP not only reflects how communities respond to environmen- tal fluctuations, but it also has important implications for re- gional carbon assessment. Unfortunately, studies based on field measurements to directly address this issue in the ex- treme environment of alpine grasslands are rare. In this study, we measured aboveground NPP (ANPP) and species richness in 40 sites across the Tibetan alpine grasslands from 2006 to 2009 to investigate the regional pattern of temporal variation in ANPP and to quantify the effects of climate fluctuation and biodiversity on this variation. The results showed that, during the 4-year period, the average ANPP varied 1.5-fold, from 83.9 to 125.7 g m 2 , with a mean coefficient of variation of temporal variation of 36.6 % across the 40 sites. Compared with other studies, alpine grasslands are not more sensitive to climate fluctuations than other grassland types. Above- ground NPP exhibited synchronous temporal variation and consistent spatial patterns over the 4-year period due to the regionally similar climatic fluctuations caused by monsoon- dominated plateau climate. Surprisingly, rainfall fluctuation had a more profound effect on the ANPP dynamics than tem- perature variation, which suggests that production in the Ti- betan alpine grasslands is primarily driven by precipitation. Therefore, ANPP in the Tibetan alpine grasslands are mainly constrained by water availability. Finally, we found a reduc- tion in interannual variation (i.e., CV) in ANPP with increas- ing species richness of plant communities, suggesting that diversity can stabilize community production in high-altitude grasslands.