Response of soil microbial community and diversity to increasing water salinity and nitrogen fertilization rate in an arid soil

The scarcity of fresh water has forced farmers to use saline water (SW) for irrigation. It is important to understand the response of the soil microbial community and diversity to saline irrigation water. The objective of this study was to determine the effects of irrigation water salinity and nitrogen fertilization rates on soil physicochemical properties, microbial activity, microbial biomass, and microbial functional diversity. The field experiment consisted of a factorial design with three levels of irrigation water salinity (electrical conductivities (ECs) of 0.35, 4.61 or 8.04dSm(-1)) and two nitrogen rates (0 and 360kgNha(-1)). The results showed that the 4.61 and 8.04dSm(-1) treatments both reduced soil microbial biomass C (MBC), microbial biomass N (MBN), basal respiration, total phospholipid fatty acid (PLFA), bacterial PLFA, fungal PLFA, and fungal:bacterial ratios. In contrast, the SW treatments increased the MBC:MBN ratio. Nitrogen fertilization increased soil MBC, MBN, basal respiration, total PLFA, bacterial PLFA, and gram-negative bacterial PLFA. In contrast, N fertilization decreased gram-positive bacterial PLFA, fungal PLFA, and fungal:bacterial ratios. Average well color development, Richness, and Shannon's Index were always lowest in the 8.04dSm(-1) treatment. Carbon utilization patterns in the 8.04dSm(-1) treatment were different from those in the 0.35dSm(-1) treatment. In conclusion, five years of irrigation with brackish or SW reduced the soil microbial biomass, activity, and functional diversity, which may cause the deterioration of soil quality. Thus, the high-salinity water (EC>4.61dSm(-1)) is not appropriate as a single irrigation water resource. Proper N fertilizer input may overcome some of the negative effects of salinity on soil microbial.