干旱区生态环境知识资源中心

Soil secondary salinization resulting from overgrazing is a serious environmental problem in arid or semiarid grasslands in northeast China, generally characterized by the dramatic increase of soil soluble salt content and the decrease of vegetative production. However, the process of soil degradation, especially the influence of soil salinization on soil physicochemical properties, enzyme activities, bacterial community composition, and metabolic diversity, has been less exhaustively assessed. This work aims to evaluate the effects of salinization level on the soil properties and to discuss the effects of metabolic profiles and bacterial community in salinized grasslands. Soil samples were collected from three grasslands with a gradient of salinization level (0.135%, 0.375%, and 1.063%, respectively). The soil properties were measured. Analysis of community level physiological profiles (CLPPs) and 16S rRNA gene denaturing gradient gel electrophoresis (DGGE) were used to determine the metabolic diversity and dominant species of a soil bacterial community, respectively. Soil moisture, porosity, total nitrogen (N) and phosphorus (P), available N and potassium (K), DNA content, microbial biomass, enzymatic activities (dehydrogenase, phosphomonoesterase, urease, and polyphenol oxidase), and metabolic function diversity all decreased significantly with an increase in salt content. Soil bulk density, pH, and available P concentration increased significantly. All of the aforementioned soil properties had significant linear relations with salt content and aboveground biomass (p < 0.001 or p < 0.05). The same DGGE profiles of the 16S rRNA gene were obtained. Sequencing of bands showed that clones retrieved were affiliated with Gamma Proteobacteria. An increase in soil salt content restrains the proliferation and metabolic activity of soil bacteria but does not affect the dominant composition of a bacterial community, and Gamma Proteobacteria is found to be the dominant phyla. Soil enzymatic activities, microbial biomass, and metabolic profiles are used to monitor soil salinization process as valuable biological indicators of soil salinization process.