Vertical distribution of soil microbial biomass and its association with shrubs from the Negev Desert

A study was conducted in the Negev Desert to illustrate the effects of desert shrubs on abiotic environmental conditions and the biomass and activity of the soil microbial community in an arid system. Soil samples were collected from the 0-50 cm depth at 10-cm intervals under the canopy of Zygophyllum dumosum, Hammada scoparia, and open spaces between them in the wet and dry seasons. Abiotic variables (soil moisture [SM], organic carbon [C _org], electrical conductivity [EC], Na ⁺, K ⁺, and Ca ⁺⁺ concentrations), and biotic variables (fungal and bacterial colony-forming units [CFUs], CO ₂ evolution rate, and microbial biomass [C _mic]), were determined. Relatively higher values of C _org, CFUs, CO ₂ evolution rate, and C _mic were recorded in the two upper (0-20 cm) layers under the canopies of Z. dumosum and H. scoparia. Conversely, EC values, Na ⁺ and Ca ⁺⁺ concentrations were relatively higher in the three deeper layers regardless of sampling season, particularly in the vicinity of H. scoparia. The environmental conditions significantly affected microbial biomass in the open spaces. Nevertheless, compared to soil moisture, organic carbon played a more important role in soil microbial biomass and activity beneath perennial shrubs. Moreover, such impacts were pronounced in the two upper layers and during the wet season.