Figure 1: Study area and sampling sites.
From: Aridity threshold in controlling ecosystem nitrogen cycling in arid and semi-arid grasslands
A 3,200 km transect in grasslands of northern China was sampled, from Gansu province to Inner Mongolia. Satellite image is from NASA (National Aeronautics and Space Administration). Aridity index (AI) is the ratio of precipitation to evapotranspiration (data from ref. 51), and covers from 0.03 to 0.57. A total of 50 sampling sites were selected (black dots) along this AI gradient. Scale bar, 500 km.
