Changes in root:shoot ratio in global biomes (a), root turnover time at specific temperature range (12–20°C, b) with precipitation. Panels c and d show patterns of species richness (c) and relative cover of C₃ and C₄ plants (d) along a precipitation gradient in southern Great Plains, USA. Root:shoot ratio data are from Mokany et al. (2006) and root turnover time data from Gill and Jackson (2000).