Effects of seasonal dry-wet alternation on soil microorganisms of tailings under different plant fiber blanket coverings in arid areas

Tailings in arid regions pose substantial environmental risks due to erosion. Natural plant fiber blankets have shown promise for ecological remediation, but their effects on the microbial communities under seasonal dry-wet alternation remain unclear. We used tailings from the Dafeng Mine in Helan Mountain in an experiment comprising four treatments: 100% straw fiber blanket, 100% coconut fiber blanket, 50% straw–50% coconut fiber blanket, and a bare-soil control (CK). Soil samples were collected during both the dry season (May) and rainy season (July) to evaluate the impacts of seasonal dry-wet alternation on physicochemical properties, enzyme activities, and microbial community characteristics. The results showed that (1) plant fiber blankets improved the tailings microenvironment; specifically, coconut fiber blankets were the most effective at increasing soil organic carbon, and total nitrogen, while seasonal precipitation activated urease activity. (2) Bacterial alpha diversity increased under all fiber blankets, whereas coconut fiber specifically boosted fungal diversity. Principal coordinate analysis (PCoA) revealed that bacterial succession was primarily driven by seasonal moisture, while fungal assembly depended on the fiber type. (3) Plant fiber blankets altered microbial life strategies (the K:r ratio). Specifically, the influx of labile carbon from straw shifted the bacterial community toward a rapid-growth r-strategy, whereas recalcitrant substances in the coconut fiber promoted the long-term colonization of K-strategist fungi. In summary, bacteria dominated the turnover of fresh organic matter, while fungi regulated the mineralization of recalcitrant substances. The 100% coconut and 50% straw–50% coconut fiber blankets achieved synergy between physical protection and biogeochemical cycling by regulating the microbial K:r ratio. These materials are thus recommended for tailings restoration in arid areas, although future research should further refine the fiber ratios for tailored applications.