Impact Of Clay Minerals And Fe Oxides On Microbial Diversity In Two Chinese Soils

The study was conducted to assess the impact of kaolinite, montmorillonite and goethite on the microbial communities in Red and Brown soils, which were collected from Changsha, Hunan and Taishan, Shandong respectively. The soils were amended with each of the minerals at ratios of 5%(dw/dw) and 15%(dw/dw). The microcosms were incubated for 3-6 months in greenhouse. Soil microbial biomass was assessed using plate counts and measurement of microbial biomass carbon. BIOLOG EcoPlate was employed to characterize the metabolic patterns of the soil microbes. The composition of the communities was investigated using phospholipid fatty acid analysis (PLFA). The experimental results were described as below.1. Mineral treatments decreased dramatically the numbers of bacteria, actinomycetes and fungi in Red soil incubated for 3 months. However, a strong recovery of soil microorganisms in the same treatments was observed 6 months after the addition of minerals. The effect of minerals on the numbers of culturable microbes in Brown soil varied with the types of microbes. Introduction of kaolinite and goethite enhanced the proliferation of bacteria and actinomycetes in Brown soil, while montmorillonite showed a negative effect. Fungi seemed not to be affected by the minerals. Soil microbial biomass carbon was inhibited by mineral amendments in both soils for 3-month incubation, but was significantly enhanced in the counterparts after prolonged incubation for 6 months.2. Ordination of the physiological (BIOLOG) data separated the microbial communities into different clusters, determined by the mineral type and concentration. Red soil amended with goethite at the rates of 5% and 15% formed distinct communities from all the other treatments which fell into two clusters determined by the incubation time. Brown soil also showed distinct clustering along incubation time. Kaolinite, montmorillonite and goethite formed contrasting clusters for Brown soils incubated for 3 months, while those incubated for 6 months less differentiated from each other. Mineral amendments exposed a positive effect on the microbial utilization of BIOLOG carbon sources for both soils.3. Principal component analysis of PLFA data denoted that mineral treatments decreased the amount of total PLFA in Red soil, goethite displayed stronger inhibitory effect on the soil microbial PLFA than kaolinite and montmorillonite. PLFA composition of Red soil amended with minerals dramatically changed as the incubation time prolonged. In contrast, mineral amendments manifested a minor effect on both the amount of total PLFA and PLFA composition for Brown soil, while total PLFA in Brown soil declined when the incubation period was extended.Conclusively, kaolinite, montmorillonite and goethite reduced the microbial biomass in Red and Brown soils in terms of culturable microbes and microbial biomass carbon, but enhanced the metabolic activity of the microbes. Distinct minerals resulted in contrasting community-level sole carbon source utilization patterns for both soils. Mineral amendments caused a dramatic shift in the amount and composition of PLFA in Red soil, while composition of PLFA in Brown soil was affected at a relatively minor degree.