Changes of soil bacterial and fungal community structure along a natural aridity gradient in desert grassland ecosystems, Inner Mongolia

Environmental aridity is increasing in several regions around the globe due to climate change. However, little is known about microbial diversity and community responses to aridity along grassland-to-desert gradients. We investigated soil bacterial and fungal diversity and composition, and associated environmental factors along an aridity gradient across grassland (G), desert-grassland (DG) and desert (D) in Inner Mongolia, Northern China. The results indicate that soil microbial diversity decreased significantly from G and DG to D. Bacteria were mostly dominated by the universal phyla Proteobacteria, Actinobacteria, Bacteroidetes and Acidobacteria. Fungal communities were dominated only by Ascomycota. Most bacterial species (58.7–69.1%) were found in all habitats with significant differences among the three vegetation types, while most soil fungal species occupied small geographic areas. Soil bacterial communities adapted to environmental changes through changes in proportions of their taxa, while fungi changed their rare taxa in response to the differences in local environments. Canonical correspondence analysis (CCA) indicated that soil C:N, salinity and regional temperature were the most important factors regulating microbial community composition. Structural equation models (SEM) revealed that C:N was the most important factor directly influencing soil microbial diversity, and SPEI was the most important factor indirectly influencing soil microbial diversity in the Mongolian desert-grassland ecosystem. Our results provide evidence that soil bacterial and fungal communities respond differently to the changes in the biotic and abiotic factors, reflecting different adaptive strategies for coping with climate change in desert grassland ecosystems.