Precipitation consistently promotes, but temperature inversely drives, biomass production in temperate vs. alpine grasslands

Comparisons of vegetation production between temperate and alpine grasslands are not well studied, and the understanding of the underlying mechanisms is still incomplete. To address this issue, we selected the Inner Mongolia and Tibet regions to conduct large-transect surveys for temperate grassland (TG) and alpine grassland (AG), respectively, in China, to reveal the universal and differential mechanisms of above- and belowground biomass production (GB, AGB and BGB) and precipitation use efficiencies (PUE) in the two grasslands. The relative importance of climatic factors on biomass and PUE is greater than that of soil and biological factors. Elevated mean annual precipitation (MAP) consistently increased GB in both TG and AG. Increased mean annual temperature (MAT) reduced GB by weakening the soil nutrient status in TG, whereas it increased GB by improving the soil nutrient status in AG. MAP promoted more AGB than BGB in TG, whereas MAT affected BGB more than AGB in AG. When the multicomponent heterogeneity of other factors in grasslands was eliminated, the effect of MAP on GB remained significant for both TG and AG. After removing the effect of multifactorial heterogeneity, however, the significant effect of MAP on PUE of the two grasslands was largely enhanced. From these results, we can conclude that climatic factors do not always exert identical effects on different grasslands. In particular, highlighting the divergent mechanisms of biomass production and precipitation use efficiency between temperate and alpine grasslands can improve the understanding of the carbon sink and hydraulic sensitivity of various grasslands.