Compensatory growth and ion balance adaptation mechanisms of Salix matsudana Koidz under heterogeneous salinity stress

Investigating 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. The 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 + , Ca 2+ , and Mg 2+ , 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. Compared 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.