Abstract
Citrus hydraulic physiology and PIP transcript levels were characterized in heavy (clay) and light (sandy loam) soils with and without treated waste water (TWW) irrigation after a summer irrigation season and at the end of a winter rainy season recovery period. Consistent reductions in clay soils compared to sandy loam were found for fresh water (FW) and TWW irrigation, respectively, in root water uptake, as well as in hydraulic conductivity of whole plant (Ks plant), stem (Ks stem) and root (Ks root). Transcript levels of most PIPs down-regulated following TWW irrigation in both soils, but relative gene expression of three PIPs was significantly higher in summer for sandy soil and FW than for clay soil and TWW; their mRNA levels was significantly correlated to Ks root. A pot experiment, which compared short term influences of saline and TWW found that both treatments, compared to FW, reduced root water uptake and PIPs mRNA levels by 2-fold after 20 days, and the decreases continued with time until the end of the experiment. These latter data indicated that salinity had an important influence. Our results suggest that plant hydraulic adjustment to soil texture and water quality occurs rapidly, i.e. within days, and is modulated by PIPs expression.
Highlights
Treated wastewater (TWW) is frequently used for irrigation in semi-arid and arid zones
Trees irrigated with fresh water (FW) grown in sandy loam had ~18% higher stomatal conductance (p < 0.01) than trees grown in clay soil irrigated with treated waste water (TWW)
Results presented here show that two irrigation seasons with the standard TWW quality used in Israel resulted in significant and important effects on tree physiology, hydraulics and the mRNA levels of most PIPs
Summary
Treated wastewater (TWW) is frequently used for irrigation in semi-arid and arid zones. TWW contains high concentrations of saline components, and organic and inorganic suspended particles compared with fresh water (FW), which can lead to a breakdown in soil structure and reduced hydraulic conductivity, increased osmotic potential, decreased aeration and reduced root growth[8]. Reductions in root function and water uptake[4,7,9,10,11,12], may be responsible for deceases in performance of plantations following TWW irrigation, as found for avocado, grapefruit, almond, peach and other fruit trees species[13,14,15]. Reduced water uptake capacity in plants grown under abiotic stress, like drought and salinity, has been linked to a decrease in root hydraulic conductance[23,29,30]
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