Fig. 6. Three dimensional plot of leaf net assimilation (A) measured at a photosynthetic photon flux density (PFD) of 1500 µmoles (photons) m^–2 s^–1 vs. leaf minus air temperature differential (T_L – T_a) vapor pressure deficit (VPD_L). Equation for the fitted plane is y = 33.93 – 2.05(T_L – T_a) – 5.24(VPD_L) with R² = 0.79, S_y.x = 3.64, and n = 166.