BackgroundInvestigating the responses of Salix matsudana to homogeneous and heterogeneous salt concentrations is crucial for the development and optimal use of saline-alkali lands. This study utilized a split-root experiment, positioning the roots of Salix matsudana in both low-salinity and high-salinity areas. Using a salt-free treatment (0/0) as a control, we applied two homogeneous salt treatments (171/171, 342/342 mmol L- 1 NaCl) and two heterogeneous salt treatments (0/342, 171/513 mmol L- 1 NaCl) to assess growth characteristics, photosynthesis, ion distribution, root vigor, and water uptake under salt stress.ResultsThe results showed that leaf biomass under heterogeneous salt treatments (0/342 and 171/513 mmol L- 1 NaCl) was 1.2 and 1.7 times greater, respectively, than under homogeneous treatments (171/171 and 342/342 mmol L- 1 NaCl). Root biomass in the low-salinity areas of the heterogeneous treatments was 2.1 and 1.3 times higher than in the high-salinity areas, with water uptake 1.6 and 1.5 times greater. This improvement was attributed to significantly enhanced root vigor in the low-salinity areas, which promoted water uptake and mitigated the inhibitory effects of salt concentration on aboveground growth and stomatal limitation. Consequently, this resulted in higher net photosynthesis rates, elevated levels of K+, Ca2+, and Mg2+, and reduced Na+ content in the leaves. Moreover, micro-area X-ray fluorescence imaging revealed that, under salt stress, Na+ was uniformly distributed across the leaves, while K+ accumulated in the main veins and, under heterogeneous salt stress, was translocated downward and redistributed to the roots in the low-salinity areas, further promoting ion balance. Compensatory growth occurred in the roots of the low-salinity areas, supporting normal plant growth.ConclusionsCompared to homogeneous salt stress, heterogeneous salt stress significantly alleviated the growth and physiological damage in Salix matsudana. Reducing salt concentrations in localized areas of saline-alkali soils may help mitigate the detrimental effects of salt stress, offering a theoretical basis for adaptive cultivation in saline-alkali regions.

Soil salinization significantly impacts the ecological environment and agricultural production, posing a threat to plant growth. Currently, there are over 400 varieties of Bougainvillea with horticultural value internationally. However, research on the differences in salt tolerance among Bougainvillea varieties is still insufficient. Therefore, this study aims to investigate the physiological responses and tolerance differences of various Bougainvillea varieties under different concentrations of salt stress, reveal the effects of salt stress on their growth and physiology, and study the adaptation mechanisms of these varieties related to salt stress. The experimental materials consisted of five varieties of Bougainvillea. Based on the actual salinity concentrations in natural saline-alkali soils, we used a pot-controlled salt method for the experiment, with four treatment concentrations set: 0.0% (w/v) (CK), 0.2% (w/v), 0.4% (w/v), and 0.6% (w/v). After the Bougainvillea plants grew stably, salt stress was applied and the growth, physiology, and salt tolerance of the one-year-old plants were systematically measured and assessed. The key findings were as follows: Salt stress inhibited the growth and biomass of the five varieties of Bougainvillea; the 'Dayezi' variety showed severe salt damage, while the 'Shuihong' variety exhibited minimal response. As the salt concentration and duration of salt stress increase, the trends of the changes in antioxidant enzyme activity and osmotic regulation systems in the leaves of the five Bougainvillea species differ. Membrane permeability and the production of membrane oxidative products showed an upward trend with stress severity. The salt tolerance of the five varieties of Bougainvillea was comprehensively evaluated through principal component analysis. It was found that the 'Shuihong' variety exhibited the highest salt tolerance, followed by the 'Lvyehuanghua', 'Xiaoyezi', 'Tazi', and 'Dayezi' varieties. Therefore, Bougainvillea 'Shuihong', 'Lvyehuanghua', and 'Xiaoyezi' are recommended for extensive cultivation in saline-alkali areas. The investigation focuses primarily on how Bougainvillea varieties respond to salt stress from the perspectives of growth and physiological levels. Future research could explore the molecular mechanisms behind the responses to and tolerance of different Bougainvillea varieties as to salt stress, providing a more comprehensive understanding and basis for practical applications.