Effect of brackish water irrigation on photosynthesis of winter jujube.

[Objective] Brackish waters including saline groundwater and treated wastewater have been increasingly used as a complimentary irrigation water resource in regions where freshwater is scarce. In the paper we investigate the effect of various concentrations of saltine irrigation water on photosynthetic characteristics of winter jujube. [Method] The experiment was conducted in 2020 in a jujube orchard, with the winter jujubes irrigated by mixtures of saltine groundwater and freshwater at concentrations of 1 (S1), 2 (S2), 3 (S3), 4 (S4) and 5 g/L (S5), respectively. In each treatment, we measured the spaciotemporal changes in soil water and salt, as well as the photosynthetic traits of the jujubes. [Result] Net photosynthetic rate, transpiration and stomatal conductance of the plant leaves varied with irrigation salinity nonlinearly, all peaking in S3 or S4. Compared with other treatments, S3 and S4 reduced the SPAD, maximum fluorescence and maximum quantum efficiency significantly. Compared to S1, S3 and S4 increased the apparent quantum efficiency, maximum net photosynthetic rate, light compensation point, and dark respiration rate, but reduced the light saturation point. These indicate that, although S3 and S4 reduced the range of available light intensity, they improved the physiological activity and efficient photosynthesis of the jujube leaves. [Conclusion] Irrigating the winter jujubes with saline water at concentration of 1-3 g/L during the fruit enlargement period can prevent light reaction inhibition and promote efficient photosynthesis. However, irrigation with water salinity exceeding 4 g/L led to salinity stress, thereby significantly reducing light energy utilization efficiency. To minimize soil salt accumulation and improve growth and development of the winter jujube, maintaining irrigation water salinity around 3 g/L is most beneficial. [ABSTRACT FROM AUTHOR]