Besides aridity, plant communities are a non-negligible factor in determining soil bacterial and fungal diversity

The impact of aridity on above- and belowground biodiversity can be profound. However, it remains unclear how drought stress influences belowground biodiversity through the complex interplay of soil quality, plant communities, and the direct effects of soil moisture deficit. In this study, we randomly selected 80 sampling plots along a 1000-km natural aridity gradient from east to west of the Inner Mongolia grasslands to identify the factors that influence soil bacterial and fungal diversity in arid and semiarid regions. Our results revealed that both soil bacterial and fungal diversity decreased with increasing aridity. Structural equation models demonstrated that aridity indirectly affected regional-scale soil bacterial and fungal diversity by regulating plant diversity and biomass. Plant biomass and community composition elicited a much stronger impact on soil fungal diversity than on soil bacterial diversity. A detailed analysis revealed that soil fungal and bacterial diversity were significantly correlated with specific plant taxa biomass. However, plant traits did not explain the positive or negative correlations between soil bacterial and fungal diversity and plant species dynamics. Instead, our data suggest that plant biomass is the primary driver controlling soil microbial (mainly fungal) diversity. Our study shows that aridity reduces soil bacterial and fungal diversity on a regional scale and indicates that aridity indirectly influences soil community composition through plant communities. Our findings indicate that plant community dynamics should be considered in assessing soil bacterial and fungal diversity on a regional scale.