Figure 7.

Simulated effect sizes of nitrogen versus CO₂ enrichment on rates of net primary productivity (NPP) that was calculated (a) globally or (b) for each plant functional type in CLM4, 4.5, and 5 (brown, turquoise, and purple symbols, respectively). In both panels, observational constraints for the nitrogen response (aboveground NPP from LeBauer and Treseder (2008)) and CO₂ response (dry matter production from Ainsworth and Long (2005)) are shown with the vertical and horizontal lines, respectively (mean ± 95% confidence interval). The right panel shows the observed (open symbols) and simulated (filled symbols) effect sizes of individual plant functional types for woody vegetation, C₃ grasses, and C₄ grasses (triangles, circles, and diamonds, respectively).