Stomatal Conductance of Lysimeter-grown Asian Pear Trees before and during Soil Moisture Deficits

Abstract

Stomatal conductance (gs) of `Hosui' Asian pear (Pyrus serotina Rehder) trees growing in lysimeters was characterized for trees in well-watered soil and after brief water deficit. The measures of water status used to interpret gs data were soil-water content, leaf water potential (ψl), and instantaneous water use (trunk sap flow by the compensation heat-pulse technique). The diurnal course and range of gs values of well-irrigated Asian pear trees were similar to those reported for other tree fruit crops. Soil moisture at the end of a midsummer deficit period was 60% of lysimeter pot capacity, and diurnal ψl reflected this deficit predawn and in the late afternoon compared to well-irrigated trees. The gs was sensitive to deficit irrigation during more of the day than ψl, with gs values <3 mm·s-1 for most of the day; these were less than half the conductances of well-irrigated trees. The reduction of gs in response to a given soil-water deficit was not as great on days with lower evaporative demand. After a water deficit, gs recovered to predeficit values only gradually over 2 to 3 days. The low gs of trees in dry soil was the apparent cause of reduced transpiration, measured by trunk sap flow, and reduced responsiveness of sap flow to fluctuations in net radiation.