Citrus trees irrigated with desalinated seawater under deficit-irrigation conditions

The current lack of natural water resources in regions such as southeastern Spain, one of the areas with a higher water deficit in the EU, is driving the use of desalinated seawater (DSW) as an alternative source for crop irrigation. Since citrus trees have proved to be sensible to Na⁺, Cl^‑, and B (phytotoxic ions that predominate in DSW), and also to water stress, its behaviour when irrigated with DSW under deficit irrigation (DI) was evaluated. One-year-old ‘Verna’ lemon trees grafted on Citrus macrophylla (CM) were grown at elevated temperatures (35/27°C) and irrigated with two types of water supplemented with Hoagland nutrients: DSW and control (distilled water). After 140 days, two irrigation treatments were applied: full irrigation (FI) or DI (a 50% volume of nutrient solution applied to FI). Seventy-five days after DI treatment was kicked off, plants irrigated with DSW or with DI treatment showed a decrease in shoot growth, probably due to the high accumulation of Na⁺, Cl^‑, and B in plants where DSW was used (which increased the number of damaged leaves). When DI was also applied to these plants, Na⁺ and Cl^‑ levels reached the highest values. Plant water potential showed a progressive decrease after DI was started and, at the end of the experiment, DSW-irrigated plants under DI treatment reached the lowest values, not only in water potential, but also in osmotic potential, that decreased due to the accumulation of phytotoxic elements and to the synthesis of osmolytes such as proline. The high stress reached by plants irrigated with DSW under DI treatments produced an increase in cellular damage, which was estimated using malondialdehyde (MDA). Since the adverse effects of irrigating citrus with DSW were aggravated under deficit irrigation, results obtained in this experiment, using DSW at a high temperature, could be useful for the management of citrus crops in the future, because climate change will increase temperatures and exacerbate the scarcity of water resources in citrus-growing areas.