Soil prokaryotic community structure is determined by a plant-induced soil salinity gradient rather than other environmental parameters associated with plant presence in a saline grassland

Soil microbial communities, which play important roles in biogeochemical cycling, are affected by plants in many ways. To understand how plants affect soil microbes, we compared soils under halophytic shrubs and herbs, whose effects on soil salinity (one of the strongest determining factors for soil microbes in saline grasslands) were different. We measured soil physicochemical properties, as well as prokaryotic abundance, community structure, diversity, and the quantified and predicted abundances of functional genes for nitrogen (N) cycling. As we intended, we found the soil salinity to be the highest in barren areas (BA), intermediate under a tamarisk crown (UC), and the lowest in herbaceous patches (HP), whereas other plant-related properties, e.g. soil organic matter content, differed between vegetated areas (UC and HP) and BA. Prokaryotic community structure and diversity changed along the soil salinity gradient, but not as a function of plant presence or absence. However, N transformation rate and N availability were not affected by the salinity gradient alone. The dominant prokaryotic groups that contributed the most to changes in prokaryotic community structure and diversity were likely not those primarily responsible for N mineralization.