Soil texture and properties rather than irrigation water type shape the diversity and composition of soil microbial communities

Around the world, water scarcity is advocating for treated wastewater (TWW) reuse, especially for agricultural irrigation. However, TWW contains inorganic substances, dissolved organic matter and microorganisms that may alter soil health and fertility. In this study, it was hypothesized that irrigation would differently alter the soil microbial communities in accordance with soil types and properties, but independent of water quality. It was further predicted that the differences in soil community would be mediated by clay content due to its physical properties and effect on organic matter content. To test these predictions, TWW and potable water (PW) were used to irrigate different soil types (clay, loam and loamy sand) for growing two Cucumis species during two cultivation seasons. The abundance, diversity and function of the soil microbial communities (bacteria and protists) were monitored in 248 samples of water and soil. The results demonstrate that the microbial communities significantly differed between water qualities, yet these differences did not carry to the irrigated soils. However, soil types significantly altered the microbial communities, particularly clay content, that correlated with a decrease in diversity indices, and changes in the composition of members of the Proteobacteria, Actinobacteria and SAR taxa. Accordingly, myriad organic compounds degradation pathways were identified in the clay soil samples. The results suggest that soils with lower clay content may be spatially segregated at the microscale, resulting in niche partitioning and higher bacterial diversity regardless of irrigation water type. Therefore, soil texture and properties shape agricultural soils’ microbial communities.