Abstract
INTRODUCTION: Soil salinization strongly shapes rhizosphere microbial communities and their functional potential in arid ecosystems. Tamarix is a key halophytic shrub in desert saline-alkali environments, yet how its rhizosphere microbiomes respond to natural salinity gradients remains insufficiently understood. Here, we compared community structure, functional potential, and potential salt-adaptation strategies across a soil salinity gradient. METHODS: Rhizosphere soils of Tamarix were collected from four sites (S1-S4) in Xinjiang, China spanning increasing salinity. Soil physicochemical properties were measured, followed by shotgun metagenomic sequencing. Taxonomic profiles and functional annotations were generated from metagenomic data and compared among salinity groups. RESULTS: Salinity was associated with clear shifts in community composition. Bacteria dominated at low-to-moderate salinity, whereas archaeal relative abundance increased at higher salinity, with Euryarchaeota becoming dominant in the high-salinity group. Functional profiling indicated that core metabolic pathways remained prevalent along the gradient, suggesting relative stability in overall metabolic capacity. However, higher salinity was accompanied by enrichment of functions linked to genetic information processing (e.g., translation and replication/repair) and ion transport, while lipid metabolism, cell motility, and signal transduction were reduced. DISCUSSION: Together, these results support a salinity-driven transition in microbial functional strategy from "growth expansion" toward "homeostasis maintenance." Under high salinity, microbes appear to allocate more resources to maintaining cellular integrity and coping with stress, consistent with the observed enrichment of genetic information processing and repair-related functions. Mechanistically, the increased representation of Na(+)/H(+) antiporter systems and V/A-type ATPases in the very high salinity group suggests that energy-dependent ion homeostasis is a prominent adaptation, helping regulate intracellular ion balance and mitigate salt toxicity. In contrast, pathways for compatible solute synthesis (e.g., betaine and ectoine biosynthesis) were relatively reduced, indicating that osmoprotection may rely less on de novo solute production and more on ion regulation and maintenance processes along this gradient. Overall, the metagenomic evidence clarifies how Tamarix rhizosphere microbiomes restructure taxonomically and functionally with increasing salinity and highlights key candidate mechanisms underpinning salt-stress adaptation. These insights provide a microbial basis for understanding plant-microbe interactions in desert saline-alkali soils and may inform ecological restoration and management in salinized regions.