Influence of vapour pressure deficit and CO2 on the thermal sensitivity of stomatal function in tropical trees

Stomatal conductance to water vapour (g<inf>s</inf>) is typically considered to operate in coordination with photosynthesis (A) to balance carbon gain and water loss in an optimal manner. However, at high temperatures that suppress A, g<inf>s</inf> has been seen to increase or remain high – reducing the predictive accuracy of some stomatal conductance models. We investigated the temperature sensitivity of leaf-level gas exchange and evaluated a temperature-dependent modification of a widely used stomatal conductance model across a temperature gradient (30 to 40°C) in three tropical tree species (Mallotus philippensis, Ficus congesta and Elaeocarpus grandis) grown and measured under near-ambient (420 ppm) or elevated (820 ppm) CO<inf>2</inf>, and under either constant or increasing vapour pressure deficit (VPD). Measured A and g<inf>s</inf>, as well as the model term g<inf>1</inf>, all exhibited a temperature sensitivity that was impacted by [CO<inf>2</inf>] and VPD regime. Importantly, under both constant and increasing VPD, g<inf>1</inf> increased with leaf temperature. These findings demonstrate that the coupling between A and g<inf>s</inf> is not static but varies with temperature and environmental context, and that incorporating a representation of this thermal sensitivity provides a tractable improvement to models of plant carbon–water exchange under future climate conditions.

New Phytologist

New Phytologist

251

1469-8137

N/A

N/A

13