Stress induced water content variations in mango stem by time domain reflectometry

Close, direct, and accurate monitoring of the plant water status may serve as a practical (irrigation scheduling) and a research (climate-environmental induced physiologic changes) tool. Methods for high-frequency capacitance measurement (e.g., time domain reflectometry [TDR]) possess the potential for high resolution dielectric measurements with minimal dependence on properties of the measured matrix. The objective of this study is to test the accuracy, response time, and sensitivity of the TDR methodology in measuring changes in water status in a mango (Mangifera indica L., Cultivar 'Kent') tree stem exposed to several perturbations concerning water, salinity, fruit load, and radiation. Under several induced stress conditions, stem and root zone water content (theta) and electrical conductivity (sigma) were simultaneously measured. Our study is distinct in its detailed and frequent measurements of stem water content (theta(stem)) using short (29-70 mm) TDR probes in trees growing in a detached medium. We have found that theta(stem) response to root zone applied salinity and water stress were negative and positive, respectively. Stem electrical conductivity (sigma(stem)) was primarily dependent on theta(stem) and only negligibly on stem cells salinity. The theta(stem) response time to water application was similar to 4 h. Two practical outcomes of our study were: (1) Because the salt content of the tree cells only slightly affected sigma(stem), stem resistivity measurements could be used to represent dielectric changes, and (2) quite short probes could be used to include young trees of slim tree branches.