Response of the soil bacterial community to seasonal variations and land reclamation in a desert grassland

Soil bacteria are important participants in biogeochemical cycles, and the stability of their community structure is not only affected by fluctuations in time and environment, but also by the participation and regulation of anthropogenic interference. With the increasing reclamation of farmland in the agropastoral transitional zone of northern China, it is imperative to understand the characteristics of soil bacterial communities in response to seasonal variations and anthropogenic reclamation. In this study, desert grassland, artificial shrubland, and desert grassland reclaimed farmland on the western side of the Mu Us Sandy Land were used as research objects. The following main results were obtained through soil sampling in April and September, and physicochemical analyses combined with 16S high-throughput sequencing: seasonal variations increased soil pH and soil water content, whereas land reclamation significantly increased soil total carbon, total phosphorus, soil available phosphorus, and soil available potassium contents. Changes in soil physicochemical properties altered the structure of soil bacterial communities to varying degrees, with Actinobacteriota and Acidobacteriota being the differential phyla among the three sampling sites under seasonal variations (p < 0.05). The relative abundance of Actinobacteriota was significantly higher in April than in September at all three sampling sites, and that of Acidobacteriota was significantly lower in April than in September. Therefore, Actinobacteriota and Acidobacteriota are key ecological indicators for predicting changes in the physicochemical properties of desert grassland soils. Actinobacteriota not only affected the complexity of the soil bacterial network, but also had a significant linear relationship with bacterial community stability. Actinobacteriota subgroups (Solirubrobacterales, Propionibacterales, 0319-7L14, and Gaiellales) were also strongly associated with soil bacterial community stability. Solirubrobacter, Gaiella, Nocardioides, Marmoricola, and Kribbella, which play crucial roles in maintaining the stability of bacterial communities, responded positively to changes in pH and soil water content. This study demonstrates the response of soil bacterial communities to environmental changes in a desert grassland and emphasizes the importance of Actinobacteriota as an indicator of soil ecosystem health.