Stress Induced Water Content Variations in Mango Stem by Time Domain Reflectometry

Abstract

Close, direct, and accurate monitoring of the plant water status may serve as a practical (irrigation scheduling) and a research (climateenvironmental induced physiologic changes) tool. Methods for highfrequency 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 (u) and electrical conductivity (s) were simultaneously measured. Our study is distinct in its detailed and frequent measurements of stem water content (u stem) using short (29-70 mm) TDR probes in trees growing in a detached medium. We have found that u stem response to root zone applied salinity and water stress were negative and positive, respectively. Stem electrical conductivity (s stem) was primarily dependent on u stem and only negligibly on stem cells salinity. The u stem response time to water application was~4 h. Two practical outcomes of our study were: (1) Because the salt content of the tree cells only slightly affected s 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.

Plant-Based Methods for Irrigation Scheduling of Woody Crops

“…By measuring θ stem with TDR in aspen, piñon, cottonwood and ponderosa pine trees, Constantz and Murphy [184] found absolute values for θ stem between 0.20 and 0.70 L L −1 , with an annual change in moisture content between 15% to 70%, depending on the species and water environmental conditions. Results of this type have been reported for many other species, as detailed by Nadler et al [157]. These authors used a TDR methodology to measure electrical conductivity in the stem of mango trees under changing water and salt conditions.…”

“…Still, devices to schedule irrigation from leaf thickness-related measurements have been developed and tested in cowpea plants under greenhouse conditions [155] and in citrus, avocado and cotton crops under open field conditions [156]. An additional problem for the use of the system in commercial farms and orchards is that, depending on the species and leaf-width gauge model, the user could be required to reinstall the sensors in new leaves quite often [157].…”

Avaliação Da Técnica Da TDR No Monitoramento De Solução Xilemática Em Cana-De-Açúcar

“…Os trabalhos encontrados na literatura (Nadler et al, 2003;Nadler et al, 2006;Hernández-Santana, 2008) foram realizados em espécies arbóreas perenes como mangueira, limoeiro e carvalhos. O uso da técnica na cana-de-açúcar é um desafio, por se tratar de uma monocotiledônea (vasos condutores difusos), semi-perene, com corte anual, e com tendência a rachamento devido à disposição vertical de suas fibras.…”

“…Uma vez que em períodos de demanda por evapotranspiração elevada os caules das árvores servem como reservatório de água, a possibilidade de medir a queda do armazenamento durante períodos de estresse hídrico pode vir a ser uma ferramenta ideal no manejo da irrigação, integrando as alterações no solo e no teor de água da planta. Nos resultados de realizados com sondas de 0,07 m de comprimento e 0,003 m de diâmetro, em mangueiras, Nadler et al (2006) obtiveram uma boa correlação com o método gravimétrico. Da mesma forma, as sondas desenvolvidas com 0,02 m de comprimento foram capazes de monitorar variações, entretanto se faz necessário uma melhor calibração dessas sondas para cada grupo de planta, para maior confiabilidade no monitoramento.…”

“…Utilizando-se de sondas de TDR, Nadler et al (2003) obtiveram resultados expressivos ao avaliar o teor de água em troncos de limoeiros que demonstraram relação entre a quantidade de água retirada do solo e a presente no caule. No caso de mangueiras (Nadler et al, 2006) verificaram que sondas menores podem trazer melhores resultados e danificar menos os tecidos das árvores. Hernández-Santana et al (2008) estudaram espécies nativas da região do Mediterrâneo na Espanha e apontaram que o TDR pode ser usado como um método de identificação do estresse hídrico em espécies arbóreas.…”