Global patterns in above-ground net primary production and precipitation-use efficiency in grasslands

The above-ground net primary production (ANPP) and the precipitation-use efficiency (PUE) regulate the carbon and water cycles in grassland ecosystems, but the relationships among the ANPP, PUE and precipitation are still controversial. We selected 717 grassland sites with ANPP and mean annual precipitation (MAP) data from 40 publications to characterize the relationships ANPP-MAP and PUE-MAP across different grassland types. The MAP and ANPP showed large variations across all grassland types, ranging from 69 to 2335 mm and 4.3 to 1706 g m(-2), respectively. The global maximum PUE ranged from 0.19 to 1.49 g m(-2) mm(-1) with a unimodal pattern. Analysis using the sigmoid function explained the ANPP-MAP relationship best at the global scale. The gradient of the ANPP-MAP graph was small for arid and semi-arid sites (MAP < 400 mm). This study improves our understanding of the relationship between ANPP and MAP across dry grassland ecosystems. It provides new perspectives on the prediction and modeling of variations in the ANPP for different grassland types along precipitation gradients.