The Impact Of Environmental Conditions On Soil Microbial Diversity And Nitrification

Soil microorganisms are sensitive indicators of the climate and soil conditions, and the change of soil quality may have a significant impact on soil. Soil environment, quality and microbial diversity may be severely affected by vegetation, land use types and agricultural management activities such as fertilizing, farming and irrigation and so on. The thesis also briefly described the research method such as community level physiological profiling (CLPP), phospholipid fatty acid (PLFA) analysis and molecular biological techniques that are widely used to study microbial diversity. Combination of these methods can provide access to information of a large amount of microorganisms, and enable a more comprehensive understanding of microbial diversity. Soil nitrification is the procedure that ammonia or ammonium salts are oxidized to nitrate under the action of microorganisms which is affected by temperature, moisture, pH, organic matter content, nitrogen content and microbial biomass and activity.In this thesis, experiments were carried out on secondary forest, eucalyptus forest, rubber plantations and banana plantations from WuShi farm in the Midwest of Hainan Province to study the effects of the change in soil use patterns on soil microbial diversity. Microbial community level physiological profiling (CLPP) analysis showed that soil microbial function diversity changes significantly with soil use patterns shifted from the forest soils to the agricultural soils. Natural secondary forest soils had the highest microbial activity (AWCD reaches 1.02 at 72h) and microbial functional diversity indices. However, when soil use pattern changed to agricultural soil such as the banana soil, the microbial activity and microbial functional diversity indices reduced significantly due to the impact of agricultural management. PLFA patterns also showed the similiar change as functional diversity. There are 47 species of PLFA in natural secondary forest, but 32 species in banana plantations. The amount of total PLFA (up to 78.41nmol/g) in natural secondary forest was significantly higher than that in banana plantations (up to 27.18nmol/g). Fungal/bacterial PLFA ratio and G+/G- bacterial PLFA ratio have different variation in the different use patterns. Hydrolyzable nitrogen, total potassium, total phosphorus, available phosphorus, organic matter and pH value were the main factors influencing microbial diversity, biomass and community structure.We also study the soil microbial diversity along the Hoh Xil railway line in Qinghai-Tibet Plateau and the effect of railway construction on soil microbial diversity. Qinghai-Tibet Plateau has a unique geographical environment, and soil nutrient content is relatively low along the railway line. CLPP analysis showed relatively low soil metabolic activity (AWCD<0.25 at 72h) and microbial biomass in this area. The soil carbon source utilization ability (functional diversity), microbial biomass and enzyme activities do not change significantly with distance change from the railway line.Finally, the effect of long-term fertilization on soil nitrification was studied taking maize-planted red soil of Jiangxi Province under long-term application of nitrogen fertilizer and organic fertilizer as the research object. The results show that long-term application of nitrogen fertilizer and organic manure could significantly increase the nitrification potential of the maize-planted red soil, and the soil nitrification potential in organic nitrogen fertilized treatments (OM, NPK+OM) is higher than that in inorganic nitrogen fertilized treatments (N, NPK).