Fig. 7
a Ordination biplot of the redundancy analysis (RDA) on microbial necromass C and geochemical variables. The variances explained by geochemical variables are shown on axes 1 (87.45%) and 2 (1.48%), respectively. The explanatory variables are indicated by different arrows: microbial necromass C by blue arrows and geochemical variables by red arrows. Arrows with narrow angles (< 90°) are positive correlations, and arrows in opposite directions (> 90°) show negative correlations. b The relative importance of geochemical variables to microbial necromass C. All variables were collected at the control plots (without N addition) at the 11 sites at which the microbial necromass C data were obtained. The circle size is proportional to the variable importance values (the importance of variance explained) based on partial least square regressions within each row. The most important variable has the largest circle, but the circle size is comparable only within a row. The adjusted R2 values are 0.882, 0.848, and 0.746 for total microbial, fungal, and bacterial necromass C, respectively (all n = 118). MAT, mean annual temperature; MAP, mean annual precipitation; C, carbon; N, nitrogen; C/N, soil carbon to nitrogen ratio