Carbon gain is coordinated with enhanced stomatal conductance and hydraulic architecture in coffee plants acclimated to elevated [CO₂]: The interplay with irradiance supply

We recently demonstrated that, under elevated [CO2] (eC(a)), coffee (Coffea arabica L.) plants grown at high light (HL), but not at low light (LL), display higher stomatal conductance (g(s)) than at ambient [CO2] (aC(a)). We then hypothesized that the enhanced g(s) at eC(a)/HL, if sustained at the long-term, would lead to adjustments in hydraulic architecture. To test this hypothesis, potted plants of coffee were grown in open-top chambers for 12 months under HL or LL (ca. 9 or 1 mol photons m(-2) day(-1), respectively); these light treatments were combined with two [CO2] levels (ca. 437 or 705 mu mol mol(-1), respectively). Under eC(a)/HL, increased g(s) was closely accompanied by increases in branch and leaf hydraulic conductances, suggesting a coordinated response between liquid- and vapor-phase water flows throughout the plant. Still under HL, eC(a) also resulted in increased Huber value (sapwood area-to-total leaf area), sapwood area-to-stem diameter, and root mass-to-total leaf area, thus further improving the water supply to the leaves. Our results demonstrate that C-a is a central player in coffee physiology increasing carbon gain through a close association between stomatal function and an improved hydraulic architecture under HL conditions.