Soil Microbial Metabolic Activity and Community Structure in Drip-Irrigated Calcareous Soil as Affected by Irrigation Water Salinity

Saline water irrigation can dramatically change the soil environment and thereby influence soil microbial processes. The objective of this field experiment was to use Biolog and high-throughput sequencing methods to evaluate the metabolic activity and community structure of soil microorganisms after 9 years of saline water irrigation. The results showed that brackish and saline water irrigation significantly increased soil bulk density and salinity, but significantly decreased soil pH, TN, SOM, MBC, and metabolic activity. The Biolog tests of sole-carbon-source utilization indicated that the brackish and saline water treatments significantly reduced the utilization of four carbohydrate sources (D-cellobiose, β-methyl-d-glucoside, D-mannitol, and glucose-1-phosphate), two amino acid sources (L-asparagine and glycyl-L-glutamic acid), two carboxylic acid sources (D-galacturonic acid and D-malic acid), and two polymer sources (Tween 80 and glycogen). Brackish and saline water increased soil bacterial richness (ACE and Chao 1 indices) but had no effect on which bacterial phyla were present. Brackish and saline irrigation water significantly increased the relative abundance of four dominant bacterial phyla (Gemmatimonadetes, Actinobacteria and Chloroflexi, Saccharibacteria). In contrast, the relative abundance of five dominant phyla (Proteobacteria, Acidobacteria, Nitrospirae, Planctomycetes, and Verrucomicrobia) was reduced by brackish and saline irrigation water. Our study suggests that soil bacterial community will form significant differences species under different irrigation water salinity, which can adapt to saline stress by adjusting the species composition. The results of this study increase understanding about the potential effects of saline water irrigation on soil biological processes.