Estimating Midday Leaf and Stem Water Potentials of Mature Pecan Trees from Soil Water Content and Climatic Parameters

摘要

Diurnal and temporal patterns of stem water potential (psi(stem)) and leaf water potential (psi(leaf)) were determined during June to Sept. 2010 and 2011 at lower (2.5 m tree, height), mid- (4.6 m), and upper (7.6 m) canopy positions for two flood-irrigated, mature pecan [Carya illinoinensis (Wangenh.) K. Koch] orchards near Las Cruces, NM. Diurnal measurements of psi(stem) and psi(leaf) at three canopy heights were correlated under both dry and wet soil conditions. However, although soil water contents at Site 2 (silty clay loam texture) remained higher compared with Site 1 (sandy loam), psi(stem) and psi(leaf) values, 7 stem particularly under dry soil conditions at Site 2, were consistently lower, showing the effect of clayey soil texture on pecan water stress. Diurnal patterns of psi(stem) and psi(leaf) indicated that measurements of psi(stem) and psi(leaf) should be made close to early afternoon (between 1400 and 1500 HR Mountain Standard Time) to evaluate mature pecan water stress, which also corresponded to maximum climatic stress conditions. Midday psi(stem) and psi(leaf) measured at 7 stem three canopy heights over several irrigation cycles during the 2010 season were correlated with one another, midday soil water content at different depths, and atmospheric vapor pressure deficit (VPD). Multiple regression analysis [between midday psi(stem) or psi(leaf) and midday theta(avg) (soil water content at 0 to 40 cm), air temperature (T-md), and relative humidity (RHmd)] during the 2010 season revealed that two-parameter regression models [psi(stem) or psi(leaf) = f (midday theta(avg) and T-md)] were the most significant for the interpretation of midday psi(stem) or psi(leaf) at both sites. Using the two-parameter model, predictions of psi(stem) and psi(leaf) measured on the both shaded and sunlit sides of trees at three canopy heights for 2011 showed good agreement between measured and predicted psi(stem) and psi(leaf) (R-2 ranged from 0.70 to 0.98). Two-parameter models derived in an earlier study generally underpredicted psi(stem) both in 2010 and 2011, which further supported the importance of the time of midday psi(stem) and psi(leaf) measurements suggested in this study.