Abstract
Degradation of semi-arid pasturelands across Central Asia presents a major ecological and economic challenge, largely driven by overgrazing, organic matter depletion, and secondary salinization. In this study, we investigated the restorative potential of slow-pyrolysis birch wood biochar applied at three rates (0, 10, and 20 t ha⁻¹) on degraded chestnut soils (Kastanozems) in the dry steppe zone of Eastern Kazakhstan. Over a two-year field trial, we monitored shifts in soil physicochemical properties, enzymatic activities, and bacterial community structure using high-throughput 16S rRNA gene amplicon sequencing. Biochar application significantly increased soil organic carbon by up to 48.6%, improved water-holding capacity, and elevated plant-available phosphorus and ammonium concentrations relative to the unamended control. High-throughput sequencing revealed marked alterations in bacterial alpha- and beta-diversity, with biochar-amended plots exhibiting elevated Shannon diversity and rich phylogenetic turnover. Taxonomic profiling indicated significant enrichment of oligotrophic taxa, including members of Acidobacteriota, Actinomycetota, and specific nitrogen-cycling families within Alphaproteobacteria, whereas potentially stress-tolerant copiotrophs declined. Microbial structural shifts were tightly coupled with enhanced urease, alkaline phosphatase, and β-glucosidase activities. These results demonstrate that biochar amendments can revitalize degraded rangeland soils by promoting microbial diversity and accelerating nutrient turnover under continental climate conditions.
