Relationship Of Nitrous Oxide Emission And Microbial Properties In Black Soil As Affected By Freeze-thaw Event

Freeze-thaw is a universal phenomenon of black soil area in Northeast China, and soil freeze-thaw region is an important N2O emissions source. In this paper, the black soil from the Key Observation Station of the Harbin Black Soil Ecology of Harbin city, Heilongjiang province, China, was investigated. The impact on N2O emissions of black soil by freeze-thaw effect was researched with different fertilization systems. The relationship between micro-organism communities and N2O productions of black soil was also researched.By dynamic monitor for the N2O emissions of black soil field, a higher N2O emission flux was observed after a snowfall, and N2O emission flux reached a higher remark in the alternation of day and night. The fertilization with duple nitrogen and the application of combined organic manure and nitrogen to black soil could significantly increase N2O emission flux of it compared with normal nitrogen fertilization. The temperature of black soil was an important factor to influence N2O emissions, and it appeared a peak of N2O emission when the temperature of black soil was near 0℃.Freeze-thaw cycles had a strong impact on N2O emission with different fertilization systems. Organic manure application could stimulate N2O to emit from black soil rapidly. N2O emission peak of black soil with only nitrogen fertilization appeared in the second freeze-thaw cycle, and the combined fertilizations made it appear several N2O emission peaks. Duple fertilization and the combined fertilization with organic and inorganic manure to black soil could increase N2O emission flux. Both phosphate and potassium fertilization both increase the number of black soil's micro-organisms, consequently increase N2O accumulative emission. Duple phosphate fertilization accelerates the N absorption of soil crops, and made the microorganism product less N2O. Amino sugar content in surface layer of black soil was an important indicator to evaluate the microorganism species and quantity, and also reflected the contribution of soil microorganism to N2O products of black soil.N2O production mechanisms of red soil and black soil were disscussed by using microbial inhibitors and acetylene inhibition, to explain microbial mechanism of black soil and different contributions of microorganism to black soil and red soil on N2O products. For black soil, N2O was mainly producted by denitrifying bacteria and fungi. Denitrifying bacteria producted N2O through denitrification, which was a dominant status and fungal heterotropic nitrification also had a considerable contribution to black soil on N2O products. In contrast, black soil producted less N2O by autotropic nitrification and chemical denitrification. For red soil, N2O was primarily producted by autotropic bacteria and fungi, and denitrification of bacteria existed in it to a certain extent. The changes of NH4+-N and NO3--N content in black soil after incubation also could explain that the main contribution to N2O products from black soil was the denitrification and heterotropic nitrification.