Water Relations of Well-watered Citrus Exposed to Cold-acclimating Temperatures

Abstract

<jats:p>This study was conducted on well-watered citrus to determine changes in water relations during cold acclimation independent of drought stress. Potted sweet orange and Satsuma mandarin trees were exposed to progressively lower, non-freezing temperatures down to 10/4 °C, light/dark temperatures, respectively, for 9 weeks in environmental growth chambers to promote cold acclimation. The trees were watered twice daily and three times on the day water relations data were collected to minimize drought stress. Although soil moisture was higher and non-limiting for plants in the cold than in the warm chamber, cold temperatures promoted stomatal closure, higher root resistance, lower stem water potential (Ψ<jats:sub>stem</jats:sub>), lower transpiration, and lower leaf ψ<jats:sub>S</jats:sub>. Leaf relative water content (RWC) was not different for cold-acclimated trees compared with the controls. Cold acclimation promoted stomatal closure at levels only observed in severely drought-stressed plants exposed to warm temperatures and where Ψ<jats:sub>stem</jats:sub> and RWC are typically much lower than what was found in this study. Ψ<jats:sub>stem</jats:sub> continued to decline the last 4 weeks of the experiment although air temperature, leaf ψ<jats:sub>S</jats:sub>, RWC, stomatal conductance (<jats:italic>g</jats:italic><jats:sub>S</jats:sub>), and transpiration were constant. The results of this experiment indicate that water relations of citrus during cold acclimation vary from those known to occur as a result of drought stress, which have implications for using traditional measures of plant water status in irrigation scheduling during winter.</jats:p>

Water and Soil Nutrient Dynamics of Huanglongbing-Affected Citrus Trees as Impacted by Ground-Applied Nutrients

“…The leaves were selected from the outermost part of the tree facing to the southwest and upper ≈ 1 2 of a tree canopy. Each leaf was covered with a transparent plastic sheath followed by aluminum foil [33][34][35]. Leaves including the petiole were cut from the shoot, and the Ψ w was measured using a pressure chamber (Model 3005 plant water status console; Soil Moisture Equipment Corporation, Santa Barbara, CA, USA) [25,36,37].…”

“…Leaves including the petiole were cut from the shoot, and the Ψ w was measured using a pressure chamber (Model 3005 plant water status console; Soil Moisture Equipment Corporation, Santa Barbara, CA, USA) [25,36,37]. After an equilibrium period of 24 h Ψ w of enclosed leaves, the measurement of the Ψ w was completed at mid-day (1200 to 1300 HR) [34,38].…”

Cold Stress in Citrus: A Molecular, Physiological and Biochemical Perspective

“…In citrus, there are many examples shown in different citrus species that photosynthesis and photosystems are damaged in the presence of low temperatures: in Citrus junos [91], in Carrizo citrange [9,42], in Fortune mandarin and Ellendale tangor [118], in Citrus deliciosa and Poncirus trifoliata var. 'Pomeroy' [119], Citrus clementina [42], Citrus medica (fingered Citron) and sweet orange [120] and satsuma mandarin [121]. In all cases, photosynthesis (Pn) decreases, stomatal closure takes place (Gs), respiration reduces and internal CO 2 concentration (Ci) rises.…”

“…Low temperatures lead to stomatal closure, decreased transpiration, and a drastically reduced osmotic potential (Ψπ), which occurs in extreme drought situations in which plants attempt to not lose water through the transpiration process. However, plants usually have the typical water potential Ψstem and RWC values typical to actively grow, with well-watered trees grown in commercial grove situations on warm sunny days [121,133].…”

Caracterización fisiológica y molecular de la respuesta de patrones de cítricos a estrés por baja temperatura

“…Las bajas temperaturas dan lugar al cierre de los estomas, disminución en la transpiración y un potencial osmótico (Ψπ) muy disminuidos como ocurre en las situaciones de sequía extrema, e la planta intenta no perder agua por el proceso de transpiración. Sin embargo, suelen tener el Ψw del tallo y el RWC en unos valores típicos del crecimiento activo de plantas en buen estado de riego cuando hay temperaturas cálidas, como ocurre en los días soleados (Kriedemann and Barrs, 1981;Barkataky et al, 2013). En este caso, es de tener en cuenta el movimiento de agua transcelular que ocurre a través de las acuaporinas.…”