Stomatal behavior of potatoes under nonlimiting soil water conditions

Field studies were conducted to examine the relative effects of net irradiance (R_n), air vapor pressure deficit (VPD) and leaf water potential (Ψ₁), on leaf conductance, (C₁) of well-watered potatoes. Conductances of sunlit, surface-layer leaves for the cultivars Russet Burbank, Kennebec and Lemhi Russet were positively correlated with R_n (r²=0.79, 0.83 and 0.62, respectively) for R_n between 100 and 650 Wm^-2. Leaf conductance (cm s^-1) for all three cultivars was described by the linear relation: C₁=0.871 +0.0028 R_n (r²=0.73). Mean C¹ for a full Russet Burbank canopy, comprised of measurements from both sunlit and shaded leaves, was also linearly related to R_n. Although VPD and Ψ₁ were significantly correlated with C₁ (r²=0.44 and 0.46, respectively), the results of multiple regression analysis showed that they had no additional effect on C¹ beyond that attributed to R_n. These results indicate that potato leaf conductance is primarily related to irradiance under nonlimiting soil water conditions.