Effects of community structure on precipitation-use efficiency of grasslands in northern Tibet

Questions(1) What are the primary factors determining the precipitation-use efficiency (PUE) in northern Tibet; (2) how does PUE respond to the gradients of biotic and abiotic factors; and (3) how do the composition and structure of plant functional groups (PFGs) affect PUE? LocationNorthern Tibet, China. MethodsA community survey of species composition, cover and above-ground net primary productivity (ANPP) was conducted within 1mx1m plots in 62 slightly disturbed sites. The effects of community features (total cover, cover of PFGs and species richness) and environmental factors [mean annual precipitation (MAP), mean annual temperature, surface soil bulk density, pH and C and N content] on PUE were identified through Pearson's correlation analyses, hierarchical partitioning and ordinary regressions. ResultsAlong the precipitation gradient, ANPP and PUE increased exponentially. Among the community features, total cover and cover of PFGs, including forbs and sedges, were the primary factors that determined PUE. The three cover variables, together with species richness, positively affected PUE and accounted for 47.6% of the total variation in PUE. Among the environmental factors, MAP, surface soil pH and N content were the most significantly related to PUE and accounted for 29.9% of the total contribution. ConclusionCommunities with high cover, species richness and nutrient content, but low soil bulk density, presented the highest PUE. At a regional scale, PUE depended mainly on plant cover, especially the cover of PFGs, namely, forbs and sedges. Environmental factors, including MAP and surface soil N and C content, positively affected PUE, whereas soil pH and bulk density negatively affected PUE. Our results highlight the importance of considering community structure to understand PUE variations in natural alpine grasslands.