Growth, Gas Exchange, and Mineral Nutrients of Albizia julibrissin and Sophora japonica Irrigated with Saline Water

Abstract

Albizia julibrissin (mimosa tree) and Sophora japonica (Japanese pagoda tree) are drought-tolerant landscape plants; however, salinity responses of these two species are not well documented. The objective of this study was to investigate the morphological and physiological responses of these two species to three salinity levels in greenhouse conditions. Two studies were conducted in the summer/early fall of 2020 and the spring of 2021. In 2020, uniform plants were irrigated weekly for the first 2 weeks and every other day for the following 3 weeks with a nutrient solution at an electrical conductivity (EC) of 1.2 dS·m−1 as a control or saline solution at ECs of 5.0 or 10.0 dS·m−1. In 2021, plants were irrigated weekly for 8 weeks with the same treatment solutions as described previously. Albizia julibrissin and S. japonica survived in both experiments with minimal foliar salt damage (leaf burn or necrosis). Irrigation water at ECs of 5.0 and 10.0 dS·m−1 reduced plant height and dry weight (DW) of both species. In the fall experiment, A. julibrissin irrigated with a saline solution at an EC of 10.0 dS·m−1 had the highest reduction in plant height (61%) compared with the control. Albizia julibrissin and S. japonica irrigated with a saline solution at an EC of 10.0 dS·m−1 had 52% and 47% reductions in shoot DW compared with the control, respectively. In the spring experiment, compared with the control, there were 72% and 45% reductions in height of A. julibrissin and S. japonica, respectively, when irrigated with saline solution at an EC of 10.0 dS·m−1. In addition, compared with the control, A. julibrissin and S. japonica had 58% and 64% reductions in shoot DW, respectively, when irrigated with saline solution at an EC of 10.0 dS·m−1. Increasing salinity levels in the irrigation water also reduced leaf greenness [Soil Plant Analysis Development (SPAD)], leaf net photosynthesis rate (Pn), stomatal conductance (gS), and transpiration rate (E) of both species. Furthermore, sodium (Na+) and chloride (Cl−) concentrations in leaves were affected by elevated salinity levels in the irrigation water. Visual score, Pn, gS, and E negatively correlated to Na+ and Cl− concentrations in leaves. But Cl− accumulation had more impact on the growth of A. julibrissin and S. japonica. In summary, both species were tolerant to saline solution irrigation up to 5.0 dS⋅m−1 and moderately tolerant to saline solution irrigation up to 10.0 dS⋅m−1.