Figure 5. Reconstructed WUE-CO₂ relationship for C3 plants during the Phanerozoic.

The curves result from the independent estimates of A based on Eq. 12 with Eq. 14a (dashed line) and Eq. 14b (solid line), and E (Eq. 10; with E_p = 7500 [µmol m⁻² s⁻¹] and δ = 2.0 mm) for the parabolic (s⋅d)-CO₂ relationship (Eq. A1).The dotted line corresponds to WUE estimates based on Eq. 5, with p_i/p_a = 0.7 and Δe = 0.03. The symbols represent values resulting from the model of Franks and Beerling [15] (based on their Fig. 10).