Fungal Denitrification In 100-year-old Tea Orchard Soil

Nitrous oxide (N2O) is one of the main greenhouse gases in the earth’s atmosphere which is controlled under the Kyoto protocol. It is involved in stratospheric ozone depletion which cause threats to human beings and other biological habitats. Soil is the most important N2O source and contributes 65% of N2O emission to atomosphere.Tea orchard soil as a typical and special agricultural soil type, are widely distributed in China. People pursuing the economic benefits of tea orchards and the qualities of tea, which leading to huge amounts of chemical fertilizers into tea orchards, especially heavy nitrogen fertilizers. Tea orchard soil is a highly acidic soil, also produce large amounts of greenhouse gas--N2O. N2O emission of soil is closely related to soil microbial activities, in the highly acidic tea orchard soil, microbial denitrification is dominant. For a long time, the foreign and domestic scholars for the studies of the greenhouse gas N2O more focused on rice paddies soil and other agricultural ecosystems, in terms of tea orchard researches, is more concentrated on the studies of the tea qualities, yields and managements. But there are not many researches on N2O emission of tea orchard soil in China.In this study, we collected soil samples from the famous place of green tea producing areas-Meijiawu tea orchard, located in West Lake district, Hangzhou, the capital city of Zhejiang province, which cultivated tea nearly 100 years. Under the conditions of laboratory, completed the basic physical and chemical properties of soil and determined soil N2O emission. By adding inhibitors to the soil, get a conclusion that fungal denitrification in the 100-year-old tea orchard soil is dominant in soil N2O flux. Studies using soil microbial traditional separation methods, combined with the advanced technologies of modern molecular biology and the analysis methods. The diversity of fungi in soil and the relative abundance of one denitrify fungus in clone library were analyzed, determine the contributions of fungi denitrification to the tea orchard soil of N2O emission.The main results of this study were as follows:1.100-year-old tea orchard soil is strongly acidic soil (pH=3.8), the N2O emission of soil under laboratory conditions measured up to 37.80 ppm,26.43 times that of control group (1.43 ppm).2. By adding different inhibitors in 100-year-old tea orchard soil, identified that fungal denitrification in the soil is dominant of the soil N2O flux. Streptomycin as inhibitor of inhibiting bacteria, causing soil N2O emission fell by 29%, is 7.69 mg/kg. And cycloheximide as inhibitor of inhibiting fungi, making soil N2O emission fell by 63%, only 2.98 mg/kg.3. Under laboratory conditions, the research isolated a denitrifying fungal strain from a 100-year-old highly acidic tea orchard soil and identified it as Penicillium decumbens TF-1, belongs to Ascomycota. Nitrate nitrogen was the only nitrogen source to produce N2O emission. And for utilization efficiencies of malic acid, fructose, glucose and other monosaccharides were higher than that complex organic carbon sources, such as sucrose.4. In 100-year-old tea orchard soil, according to 18S rRNA gene soil fungi clone library analysis, the diversity of soil fungi is abundant and divided into 22 OTU, classified as 5 subdivisions:Ascomycota, Basidiomycota, Mucoromycotina, Chytridiomycota and Zygomycota. The strain TF-1 has a relatively high abundance in the 100-year-old tea orchard soil fungal community, which proved the isolated strain making a certain contributions to the soil N2O emission.