Figure 4. Sensitivity of the soil water response to CO₂ enrichment for the entire data set.

The response index was calculated as the soil water content under elevated CO₂ divided by the soil water content under ambient CO₂. The closed circles are the observations, with the solid black line providing a linear regression. The red lines represent the 95% confidence intervals of the observations and the dashed grey lines represent the 95% confidence interval of the model. m is the slope of the regression line.