Stomatal conductance increases with rising temperature

Abstract

Stomatal conductance directly modifies plant water relations and photosynthesis. Many environmental factors affecting the stomatal conductance have been intensively studied but temperature has been largely neglected, even though it is one of the fastest changing environmental variables and it is rising due to climate change. In this study, we describe how stomata open when the temperature increases. Stomatal conductance increased by ca 40% in a broadleaf and a coniferous species, poplar (Populus deltoides x nigra) and loblolly pine (Pinus taeda) when temperature was increased by 10 °C, from 30 °C to 40 °C at a constant vapor pressure deficit of 1 kPa. The mechanism of regulating stomatal conductance by temperature was, at least partly, independent of other known mechanisms linked to water status and carbon metabolism. Stomatal conductance increased with rising temperature despite the decrease in leaf water potential, increase in transpiration, increase in intercellular CO₂ concentration and was decoupled from photosynthesis. Increase in xylem and mesophyll hydraulic conductance coming from lower water viscosity may to some degree explain temperature dependent opening of stomata. The direct stomatal response to temperature allows plants to benefit from increased evaporative cooling during the heat waves and from lower stomatal limitations to photosynthesis but they may be jeopardized by faster depletion of soil water.

Keywords: Ball-Berry model; elevated temperature; evaporative cooling; global change; heat waves; photosynthesis; stomatal conductance.

Figure 1.

Stomatal conductance (g_s) of poplar (left panel) and loblolly pine (right panel) and its dependence on air temperature and vapor pressure deficit (VPD). Plants were measured in high soil moisture conditions and ambient [CO₂]. Error bars indicate standard error of the mean (n = 6). Linear regression was used to fit the data at the same temperatures.