Fig. 4From: Stomatal conductance limited the CO2 response of grassland in the last centuryPhysiological correlates of long-term δ18Ocellulose-change: relationship between long-term change in δ18Ocellulose and change in intrinsic water use efficiency (Wi) (a), hay yield (b), and nitrogen acquisition (c), for individual treatments. Long-term changes were calculated as in Fig. 3. The dashed lines and the shaded areas represent the regression line ± CI95%Back to article page