Figure 1. Global climate map and a comparison of mean effect size and soil water response under elevated CO₂.

(A) Site locations of the CO₂ enrichment experiments together with globally distributed climate zones based on a standard aridity index formulation (precipitation/potential evapotranspiration); (B) Mean effect size of soil water content under elevated CO₂ for the entire data set, under dryland and non-dryland regimes. The effect size was calculated as the natural log of the magnitude of an experimental treatment mean (the soil water under elevated CO₂) relative to the control treatment mean (the soil water under ambient CO₂); The dashed line indicates the threshold of statistically significant CO₂ effect on soil moisture. The effect is positive when above the line and vice versa. (C) Enhancement of soil water content under elevated CO₂ for dryland versus non-dryland regimes. The number of cases is shown in brackets. Error bars are bootstrapped confidence intervals (CI). All the statistics are significant at P < 0.05. The map was generated using ArcGIS for Desktop 10.3.1 (http://www.arcgis.com).