QUANTIFYING SAP FLOW RESPONSES TO SOIL AND PLANT WATER STATUS AND CLIMATE IN NECTARINE TREES

Abstract

Measurements of xylem sap flow (SF) and its response to soil and plant water status and climatic parameters can help to develop better water status indicators, which may help to manage irrigation based on orchard specific conditions. SF was measured with thermal dissipation probes in drip irrigated 12 years old nectarine (Prunus persica var nectarine) trees in Northern Israel. SF probes, automatic sensors for monitoring soil and plant water status, and a meteorological station were installed in standard irrigated plots and in a separate plot for experimental drying and wetting. Mid-day stem water potential (MSWP) was monitored periodically in all plots. SF and leaf conductance increased with leaf area development at the beginning of the season. Variations observed in the drying and wetting plot during four drying cycles before, and one after harvest, were instrumental in finding relationships between SF and canopy conductance and soil and plant water status and climate variables. SF was more variable and less sensitive than other water status measures. During drying, SF decreased by up to 40 % and relative to ET0 it decreased by up to 60%. When expressed relative to the irrigated trees SF decreased by up to 35%, and MSWP by 70%. Similar responses were observed in the post-harvest period. Signal to noise ratios were calculated for the sensors. During the drying cycles SF and conductance were significantly correlated with MSWP, and responses to reduced soil water were quantified. INTRODUCTION Differences in nectarine (Prunus persica var nectarine) sensitivity to water stress at different developmental stages are challenging for irrigation scheduling, similar to other deciduous fruit trees (Ortuno et al., 2004; 2006; Conejero et al., 2007, Fernandez et al., 2011, Biel et al., 2011). For improving agricultural irrigation efficiency it is critical to quantify plant and soil water status. The former can be monitored with manual tools, such as the pressure chamber for measuring leaf water potential, porometry for leaf conductance or with automatic soil and plant sensors (Jones, 2008). For automatic irrigation scheduling it is necessary to replace the manual tools, even though they are believed to be the most precise for setting irrigation timing in fruit trees (Casadesus et al., 2012). The growing shortage of water available for irrigation in many parts of the world increases the need for savings and increased efficiency in water use (Chalmers et al. 1986; Matthews et al., 1990; Fereres et al., 2003; Naor, 2006; Kanety, 2010; Casadesus et al., 2012). For this we need to have better automatic irrigation tools that can quantify water status more precisely (Remorini and Massai, 2003). One automated water status indicator could be the measurement of SF in the tree trunk (Naor and Cohen, 2003; Ortuno et al., 2006; Biel et al., 2012) but few studies have compared the performance of SF and other sensors with tree water status parameters like stem water potential (e.g. Biel et al., 2012).