In this study, the near-naturalization process of Pinus tabulaeformis plantations in Baxianshan National Nature Reserve was divided into three stages depending on the proportion of P. tabulaeformis present, resulting in the following categories: the P. tabulaeformis forest stage, the mixed forest stage, and the near-natural forest stage. Natural secondary forests were selected as a control. We assessed alterations in the soil’s fungal functional structures from three aspects: functional mode, vegetative mode, and growth mode, and their responses to vegetation and soil factors were also explored. The results showed that ectomycorrhizal, saprophytic, and plant pathogen types were dominant in the functional mode, and plant pathogens were most abundant in the P. tabulaeformis forest stage. Meanwhile, ectomycorrhizal fungi were the least abundant in the near-natural forest stage. In the vegetative mode, saprophytic, pathophysiological, and symbiotic types were dominant, and pathophysiological types were the most abundant in the P. tabulaeformis forest stage. In the growth mode, microfungi dominated, and the abundance of clavarioid decreased with near-naturalization. The degree of variation in functional structure in the three dimensions increased with near-naturalization, but the structure of natural secondary forests converged. The species composition of tree layer obviously affected the abundance and functional structure of fungi in the three modes, among which Quercus mongolia and Carpinus hornbeam were the most significant. The soil’s pH and nitrate content significantly affected the structure of the functional mode, and the soil’s dry matter content and C/N ratio significantly affected the structure of the vegetative mode. In this study, we explored the interaction between the plant community and soil ecological system during the near-naturalization process of plantations in terms of soil fungi functions, further clarifying the role of soil functions in the succession of plant communities and providing a new perspective on the in-depth exploration of ecosystem interactions during the succession of plantations.

Background/Objectives: Ziziphus jujuba var. spinosa (sour jujube) is a traditional medicinal plant with remarkable tolerance to abiotic stresses, particularly salinity. However, the regulatory mechanisms underlying its salt stress tolerance remain unclear. NHX genes play a crucial role in plant adaptation to salt stress by mediating Na⁺/K⁺ transport to maintain intracellular ion homeostasis and pH balance. Although the NHX gene family has been characterized in many plant species, its functional characteristics in sour jujube have not yet been systematically investigated. Methods: In this study, using Arabidopsis thaliana as a reference, we identified NHX genes in sour jujube through genome-wide analysis and molecular approaches, and systematically analyzed their phylogenetic relationships, chromosomal locations, conserved motifs, gene structures, cis-regulatory elements in promoter regions, and expression patterns under abiotic stresses, particularly salt stress. Results: The results revealed the presence of eight NHX genes distributed across six chromosomes in sour jujube, which were classified into three subfamilies: Vac-class, Endo-class, and PM-class. Members within the same evolutionary clade exhibited high structural conservation in motif composition and gene architecture. Except for the PM-class, all other clades contained amiloride-binding sites (FF(I/L)(Y/F)LFLLPPI). Analysis of cis-regulatory elements indicated that the promoter regions of these genes were enriched with elements related to defense responses, stress adaptation, and phytohormone signaling, further supporting their role in plant environmental adaptation. Additionally, the qRT-PCR analysis showed that most of the ZjNHX genes in both roots and leaves are up-regulated by salt. Notably, ZjNHX1 expression in roots increased approximately 40-fold within 3 h, whereas ZjNHX2 and ZjNHX3 were strongly induced in leaves under prolonged salt exposure. Conclusions: Taken together, this work gives a detailed overview of the ZjNHX genes and their important roles in response to salt stress in sour jujube. Our findings also provide a foundation for further functional characterization of this gene family.