Effect of salinity on ion homeostasis in three halophyte species, Limonium bicolor, Vitex trifolia Linn. var. simplicifolia Cham and Apocynaceae venetum

Limonium bicolor, Vitex trifolia Linn. var. simplicifolia Cham and Apocynaceae venetum are halophyte species with ecological restoration function of saline soil that are widely distributed in coastal areas around Bohai Sea in China. The mechanism of response to salt stress is different between them. The salt-tolerance mechanism, especially for ion homeostasis, of these halophytes varies and is not properly understood. The purpose of the work was to reveal the effect of salinity on ion homeostasis in these three halophyte species. Plant growth, leaf succulence, Na⁺, K⁺ and Cl⁻ concentrations, as well as ion flux were examined at various concentrations (0–100%) of artificial sea water after 10 days. The results showed as follows: the growth of L. bicolor was obviously stimulated under salt stress, while V. trifolia Linn. var. simplicifolia Cham and A. venetum was strongly inhibited. The contents of Na⁺ and Cl⁻ increased with salinity in the three halophyte species, in both the leaves and roots. The accumulation of K⁺ in roots was promoted by salinity except in L. bicolor subjected to 100% artificial sea water concentration. L. bicolor roots showed a lower net Na⁺ efflux compared with the control. By contrast, V. trifolia Linn. var. simplicifolia Cham and A. venetum roots retained a greater capacity for net Na⁺ efflux compared with the control. L. bicolor and V. trifolia Linn. var. simplicifolia Cham roots exhibited a lower and higher net Cl⁻ influx, respectively, than the control, but the differences were not significant. By contrast, A. venetum roots exhibited a Cl⁻ efflux compared with the control. L. bicolor and V. trifolia Linn. var. simplicifolia Cham roots reduced net K⁺ efflux, and L. bicolor even appeared to exhibit a K⁺ influx at certain points in time, whereas A. venetum strongly increased net K⁺ efflux compared with the control. The accumulation and partitioning of ions differed between the three halophyte species, and the salt-tolerance ranking from high to low was L. bicolor, V. trifolia Linn. var. simplicifolia Cham, and A. venetum.