Increasing soil pH enhances the network interactions among bacterial and archaeal microbiota in alpine grasslands of the Tibetan Plateau

Abstract Background: Soil functioning and processes are driven by complex microbial interactions. It is therefore critical to understand the co-occurrence patterns of soil microbiota, especially in fragile alpine ecosystems. Here we explored the geographic patterns of the topological features and the major drivers shaping the topological structure of the co-occurrence network for bacterial and archaeal microbiota in alpine grasslands of the Tibetan Plateau based on high-throughput sequencing. Results: Soil pH was the most important environmental variable for predicting the topological features of the microbial network at both network and node levels. Associations among soil microbiota were enhanced with increasing pH (5.17–8.92), and the network was the most stable at neutral pH (7). Node-level topological features suggested that taxa of the high-pH cluster had more important roles in maintaining complex network connections than taxa of the low-pH cluster. Network-level features revealed closer relationships among soil microbiota in the steppe ecosystem than in the meadow ecosystem. Archaeal operational taxonomic units (OTUs) with higher values for node-level topological features appeared to be more important than bacterial OTUs in maintaining complex connections. The co-occurrence patterns of bacterial OTUs with lower node-level feature values followed a power-law distribution, whereas those of archaeal OTUs did not. Conclusions: Soil pH plays a decisive role in determining the complex interactions among soil microbiota in alpine grassland ecosystems of the Tibetan Plateau, with a more stable co-occurrence network at neutral pH. Bacterial and archaeal taxa, which occupy distinct network niches, have closer relationships in alpine steppe than in alpine meadow ecosystems.