Figure 5 . (a) Belowground community-level water source partitioning (mean ± SE, unitless) in the four-species mixtures for each sampling date. Letters denote significant differences between dates. (b) Relationship between the belowground community-level water source partitioning and the aridity index (P/PET) in the four-species mixtures. Colors represent the aridity index with a gradient from the driest (light blue) to the wettest (dark blue). The line represents the significant linear regression between water source partitioning and P/PET.