Stomatal Conductance and Photosynthesis in a Mature Scots Pine Forest. II. Dependence on Environmental Variables of Single Shoots

Abstract

SUMMARY (1) Water use by coniferous plantations may lead to water shortages in regions where water is a scarce resource. To be able to estimate transpiration in relation to assimilation of carbon over a year, it is necessary to know how stomatal conductance and CO2 uptake change with environmental variables. (2) The stomatal conductance and photosynthesis of current-year shoots of Scots pine (Pinus sylvestris) growing in eastern England were measured at different levels in the canopy and correlated with local values of the main environmental variables. (3) The major determinant of stomatal conductance during the growing season was atmospheric water vapour saturation deficit, except during periods when air temperature was less than 10 OC or incident quantum flux density was low, particularly at dawn and dusk. Stomatal conductance declined sensitively with water vapour saturation deficit between 0- 5 and 1 * 5 kPa but then remained constant at larger deficits. (4) Light-saturated values of stomatal conductance decreased with depth in the canopy but it was not possible to determine the response curve between stomatal conductance and light adequately from the data.