Soils in the arid and semiarid regions face to salinization that adversely affect plant growth and cause crop yields and quality to decrease. In Ningxia Hui Autonomy province of China, severity of soil salinization differs in different regions. As arbuscular mycorrhizal fungi (AMF) are important group of soil biota, understanding the relationship between soil salinization and the AMF is critical for successful utilization of AMF in different types of saline conditions. To test whether and how soil microbial community and soil salt stress will interactively affect arbuscular mycorrhizal fungi, we conducted a study by sampling soils from three types of saline soil with the typical plant communities in Ningxia. The three types of saline soils were alkaline soil, meadow solonchak and saline anthropogenic-alluvial soil. Four locations were sampled for each soil type. We first tested the structure of microbial community and the functional diversity of microorganism in the rhizosphere soil by dilution plating and ECO-plate technique, Then we examined measured the spore density and colonization rate of AMF. Soil property and base cations and anions were also measured. Multivariate statistical analyses were conducted to compare the effect of soil microbial community and soil factors on AMF in different kinds of salinized soils. The relationship among the spore densities, colonization rates of AMF in plant rhizosphere, the structure and function of microorganisms communities and soil physical and chemical characteristics were analyzed.
The results showed that spore density of AMF differed in soil types. The highest spore density was found in Xidatan I, and that the lowest was found in Huinong. The quantity and the distribution of microbes in rhizosphere were shown as follows: bacteria> actinomycetes> fungi. Bacteria was the dominant community in all the four sampling sites. The major microbial community was amino acid metabolism groups for the meadow solonchak in Hongsipu site, The bacteria of amine compounds metabolism groups and the bacteria of carbohydrate metabolism groups were the dominant species in Huinong and in Xidatan respectively. Except in Xidatan II, the rhizosphere microorganism had a lower ability of metabolism on aromatic compounds in all the other three locations.
Our results also indicated that the ability of carbon source utilization of soil microorganisms was significantly different. With incubation time increasing, the average well color development(AWCD) tended to increase in the ECO plate. Ninety-six hours after incubation, AWCD in the ECO plate for four sampling sites was ranked as the follows: Huinong> Xidatan I>Xidatan II> Hongsipu. The relationship between spore density of AMF and the microbe carbon metabolism groups was very complex. The spore density of AMF in Huinong was positively correlated with the bacteria of polymer compounds metabolism groups and had a significant positive correlation with microbial carbohydrate metabolism groups in Xidatan. Redundancy analysis (RDA) indicated that soil organic matter, total salt, total nitrogen, available nitrogen and the other soil factors including HCO₃^-,Na⁺, Cl^- could be used to explain the relationship between the spore density of AMF and the soil environmental factors in different soil sampling sites. There was close relationship among soil organic matter,total salt,total nitrogen, available nitrogen and spore density, and colonization rate. The spore density and colonization rate of AMF had close relationships with HCO₃^-. The colonization rate of AMF was promoted owing to the higher concentration of HCO₃^-. But, there was a negative correlationship between the content of Na⁺, Cl^- and colonization rate of AMF. To some extent, the colonization rate of AMF was inhibited by the higher concentration of Na ⁺, Cl^-. Our results suggested that the different effects of rhizosphere soil microbial community and soil factors on arbuscular mycorrhizal fungi may be due to the differences of salt components and soil nutrition in salinized soils.
The result from our study provide important data for understanding the diversities of AMF and for promoting reasonable development and utilization of salinized soils in Ningxia.