Physiological and Transcriptional Mechanisms Underlying Salt Tolerance in Quercus acutissima Regulated by Funneliformis mosseae

Quercus acutissima is an important tree species of coastal shelterbelts in eastern China; however, soil salinization severely constrains its growth and ecological benefits. Funneliformis mosseae can enhance plant stress resistance, yet the mechanisms by which it regulates salt tolerance in Quercus acutissima remain unclear. In this study, a two-factor pot experiment was conducted on half-sib families of Quercus acutissima with four salinity gradients (0‰, 2‰, 4‰, and 6‰, corresponding to 0%, 0.2%, 0.4%, and 0.6% (w/w) NaCl, respectively) and four inoculant doses (0, 10, 20, and 30 g), with three biological replicates per treatment, and the regulatory pathways were dissected by combining physiological measurements with transcriptome sequencing of functional leaf tissues collected from four selected treatment groups (the uninoculated control, mycorrhizal inoculation alone, salt stress alone, and salt stress combined with mycorrhizal inoculation). The results showed that inoculation with Funneliformis mosseae under salt-free conditions induced a slight stress-like response in Quercus acutissima; inoculation enhanced salt tolerance only under low-salt conditions (≤2‰ NaCl, mass concentration), with the 30 g high-dose inoculant being the most effective; salt stress promoted excessive root lignification and xylem embolism, whereas symbiosis with Funneliformis mosseae alleviated this damage. Successful root colonization by Funneliformis mosseae was established in all inoculated treatments, confirming the formation of a functional mycorrhizal symbiosis under both salt-free and salt-stressed conditions. The pentose phosphate pathway, the inositol phosphate–Ca2+ signaling pathway, and multiple hormone-related pathways coordinately regulated salt tolerance. This study provides a theoretical basis for cultivating Quercus acutissima in salinized soils, offers practical support for afforestation of Quercus acutissima on saline lands in the Yellow River Delta, and contributes to improving the quality and efficiency of coastal shelterbelts.