Comprehensive evaluation of salt tolerance in six oak species ( Quercus spp.): Unraveling growth-resistance trade-offs

In the context of increasing soil salinity worldwide, it is crucial to understand the salt tolerance of landscape species including oaks. Here, we comprehensively evaluated the salt tolerance of six oak species (Quercus aliena, Q. acutissima, Q. texana, Q. nuttallii, Q. shumardii, and Q. nigra) by using continuous NaCl treatment, identifying Q. aliena as the most salt-sensitive and Q. nigra as the most salt-tolerant in the tested oak species. The results showed that in Q. nigra, the plant height was inhibited the most, but the Fv/Fm did not significantly altered. The research highlighted growth-resistance trade-offs among various oak species to promote salt tolerance. Q. nigra keeps slow growth rate to enhance the salt tolerance and tend to accumulate more Na+ in stems. Correlation and PCA analyses revealed that the decrease of plant height, Fv/Fm, and the K+/Na+ ratio in roots are key indicators of salt tolerance in oaks, while proline is not a suitable indicator for evaluating salt tolerance in oak species. Our findings not only provide the first comprehensive evaluation of salt tolerance in these oak species but also uncover trade-off strategies between growth and tolerance. By proposing key indicators for further salt-tolerance assessments and offering potential breeding materials, this work provides valuable insights for developing salt-tolerant oak varieties.