Deficit Irrigation Applied to Lemon Trees Grafted on Two Rootstocks and Irrigated with Desalinated Seawater

Abstract

The use of desalinated seawater (DSW) for irrigation in semi-arid regions is taking hold. Citrus tolerance to ions that predominate in DSW and water stress depends on the rootstock. Deficit irrigation was applied to DSW-irrigated lemon trees and grafted on rootstocks with different tolerance (Citrus macrophylla (CM) and sour orange (SO)). Plants were irrigated with DSW or Control treatment (distilled water), and, 140 days later, irrigation treatments were started: full irrigation (FI) or DI (50% of the volume applied to FI). After 75 days, differences between CM and SO plants irrigated with DSW and under DI were found. The higher concentrations of Cl− and Na+ in CM and B in SO were the main causes of shoot growth reduction. The osmotic adjustment of CM plants was made possible by the accumulation of Na+, Cl−, and proline, but SO failed to adjust osmotically. In CM and SO plants, photosynthesis reduction was due to lower chlorophyll levels, but also to stomatal factors (CM plants) or alterations of the photochemical machinery (SO plants). Finally, unlike CM, SO had a good antioxidant system. In the future, knowing the different responses of CM and SO under these stressful conditions could be useful in citrus-growing areas.

Physiological Responses of a Grapefruit Orchard to Irrigation with Desalinated Seawater

“…These concentrations were found to be within the range reported in previous studies [ 3 , 22 , 32 ]. In fact, recent studies [ 20 , 21 , 22 ] have detected toxic B levels in the leaf and a decline in physiological parameters in lemon trees with similar DSW water quality properties. In this sense, the second RO stage performed on the farm was able to decrease the overall DSW concentration of B below the phytotoxic threshold ( Figure 1 ), thereby avoiding possible detrimental effects on the tree.…”

“…Those soils irrigated with DSW had the highest B concentration due to its higher concentration in the water source. Recent studies using DSW for citrus irrigation also found important accumulations of B in soils irrigated with DSW [ 21 ], albeit without the B content exceeding medium–high levels for agricultural soils (0.21–1.10 mg kg −1 soil) [ 34 ]. Consequently, the lower the proportion of DSW in the irrigation blend, the lower the concentration of B in the soil (DSW > MW > FW > DSW–B; Figure 2 ).…”

“…In general, lower g s on DSW-irrigated trees with respect to the rest of the trees was observed throughout the experiment, which produced lower E and A , although they were only significantly different in July. Previous experiments with young lemon trees under controlled conditions showed a decrease in A but not in g s or E due to the irrigation with DSW, which produced a decrease in the intrinsic water-use efficiency [ 20 , 21 ]. However, no decrease in A/g s was observed due to the irrigation with DSW in this experiment.…”

“…Overall, their ability to control these environmental stresses seems to depend on the rootstock [ 18 , 19 ]. Recent research conducted under controlled conditions has shown that the rootstock can modulate the citrus plant response to DSW irrigation [ 20 , 21 ].…”

“…When referring specifically to physiological and nutritional effects, the studies available in the literature to date have mainly evaluated the detrimental effects of using DSW for citrus irrigation under controlled conditions. The research showed that high soil salinity and the accumulation of B, Cl − , and Na + in citrus trees can impede the uptake of certain nutrients due to chemical competition and produce specific toxicity problems in the plants [ 20 , 21 ]. When DSW was used to irrigate a mandarin orchard, non-significant toxic responses (leaf toxic ions accumulation, low plant water relations, or low crop gas exchange) were observed; this was likely due to the young age of the trees [ 3 ].…”