Precipitation and aridity index regulating spatial patterns of vegetation production and species diversity based on alpine grassland transect, Tibetan Plateau

31 Although the relationship between the aboveground net primary production (ANPP) and species 32 diversity (SR) have been widely reported, there is considerable disagreement about the fitting 33 patterns of SR–ANPP, which has been variously described as ‘positive’, ‘negative’, ‘unimodal’, 34 ‘U-shaped’ and so on. Not surprisingly, the effect-factors including precipitation, aridity index and 35 geographic conditions (e.g., altitude, longitude and latitude) on ANPP and SR continue to interest 36 researchers, especially the effects at high altitude regions. We investigated ANPP and SR from 113 37 sampled sites (399 plots) across alpine meadow and steppe in the Tibetan Plateau, which included 38 Tibet, Qinghai and Sichuan province. The effects of various environmental factors (precipitation, 39 temperature, aridity index, altitude, longitude, latitude and vegetation type on SR and ANPP) were 40 explored. The results indicate that a unimodal pattern was confirmed between ANPP and SR in 41 alpine steppe (R=0.45, P<0.0001), alpine meadow (R=0.4, P<0.0001), and all samples across 42 alpine grassland (R=0.52, P<0.0001). For the aboveground net primary production, the 43 appropriate precipitation and aridity is 600mm and 42, respectively. Under the same moisture 44 conditions, the maximum value of diversity is 0.75. Longitude (R=0.69, P<0.0001) and altitude 45 (R=0.48, P<0.0001) have positive and negative effects on aboveground net primary production, 46 and a similar relationship exists with diversity (R=0.44, P<0.0001 and R=0.3, P<0.0001). The 47 same patterns of diversity and production responding to precipitation and the aridity index were 48 evident in alpine steppe and meadow, and a unimodal pattern was confirmed between ANPP and 49 SR in both locations. 50