Several lines of evidence showing the existence of nonlinear responses to changes in precipitation for root biomass (Bond-Lamberty and Thomson 2010; a), belowground net primary production (BNPP) from grasslands (Hui and Jackson 2006; b) and soil C content from Tibetan’s grasslands (Yang et al. 2008; c) and from grasslands in central Oklahoma (Zhou et al. 2009; d). In panel d, data from deserts are in Majove, Chihuahua, Sonoran and Colorado Plateau in USA and Gurbantonggut and Kelamayi in China) (Bell et al. 2009; Fernandez et al. 2006; Li et al. 2010; Scheffer and Carpenter 2003; Wheeler et al. 2007; Zhang et al. 2009).