Changes in the Soil Microbiome of Arable Soils in the Permafrost-Affected Zone During Their Transition to a Fallow State

Agricultural land abandonment is widespread in high-latitude regions, yet its effects on soil microbial communities in permafrost ecosystems remain insufficiently understood. In this study, we used a 0–25 year chronosequence of abandoned soils in the Yamalo–Nenets Autonomous Okrug to analyze the succession of soil microbial communities and compared them with mature reference Podzols. Soil physicochemical properties, microbial community composition, and potential functional changes were systematically assessed using 16S rRNA gene sequencing, multivariate statistical analyses, and functional prediction. The results showed that, in mature soils, SOC was the key factor driving microbial community variation, whereas in agricultural and abandoned soils, available nutrients were the main factors influencing microbial community structure. The abandonment process also constrained soil microbial mineralization. The dominant microbial phyla mainly included Proteobacteria, Acidobacteriota, Verrucomicrobiota, Bacteroidota, and Actinobacteriota, while the relative abundances of other taxa differed markedly among land-use stages. Agricultural soils were dominated by copiotrophic microbial groups, whereas microbial communities in abandoned soils gradually shifted toward oligotrophic groups with increasing recovery time, and some taxa associated with the degradation of complex carbon substrates also increased in abundance. Functional analysis further indicated that carbon and phosphorus cycling functions in soil microbial communities exhibited a certain degree of functional redundancy, whereas nitrogen-cycling functions depended more strongly on specific microbial taxa. Land abandonment promoted an increase in the abundance of genes related to microbial carbon metabolism in soil. However, even after 25 years of abandonment, microbial community composition and functional potential had not fully recovered to the level of mature reference Podzols, indicating that agricultural disturbance exerts long-term legacy effects on soil microbiomes in permafrost-affected regions.