| Global warming has seriously affected the balance of ecosystems and brings great challenges to human survival and development.The accumulation of greenhouse gases is the main reason of global warming.The characteristics of N2O with high warming potential and long residence time in the atmosphere have received widespread attention from domestic and foreign scholars in recent years.Soil is the largest source of N2O gas,accounting for more than 80%of the N2O emissions from the biosphere.Soil microorganisms are directly involved in the process of material cycle and energy flow in the soil,which in affects N2O emissions.Soil moisture is an important part of the soil system.The black soil in Heilongjiang province is characterized by its unique geographical feature that fertile and high yield.However,frequent changes in soil moisture have a certain effect on the process of nitrogen transform and N2O emissions in soil.In this study,we focused on the black soil collected from Heilongjiang Academy of Agricultural Sciences with a laboratory incubation method and molecular techniques such as DNA extraction,agarose gel electrophoresis,real-time quantitative PCR to study nitrogen conversion rate,microbial functional gene abundance and N2O emissions in different soil moisture conditions,and explore the effect of soil moisture on nitrogen transformation and microbial activities.In order to establish a reasonable water management model for Heilongjiang black soil in actual production for reducing N2O emissions.The main research conclusions are as follows:(1)After 60 days of culture under different water conditions,there is a positive correlation between nitrification and denitrification functional gene abundance and soil moisture content.The AOA amoA gene abundance in soil is much higher than AOB amoA gene,AOA amoA gene abundance is high in flooded state due to extreme environmental tolerance.The soil moisture content of 40%WHC was more suitable for AOB.Low soil moisture has no significant effect on denitrifying functional genes,nirS gene only reproduces in the flooded state but the optimum soil moisture conditions for nosZ gene is 80%WHC.(2)Mineralization,nitrification and denitrification rate are positively correlated with soil moisture within a certain range under gradient increasing moisture condition and 80%WHC is the critical soil moisture content.Gradient increasing moisture changes have an adverse effect on NO3--N accumulation,but have no significant effect on NH4+-N content,increasing AOA amoA and nosZ genes abundance.80%WHC is the most suitable soil moisture condition for AOA.The abundance of AOB amoA gene is consistent with the change of nitrification rate and is the main driver of nitrification process.80%WHC is the optimum soil moisture for denitrifying microorganisms.Denitrification is more complete and N2 is the main product under constant 80%WHC.The maximum N2O emission appeares at 60%WHC with gradient increasing moisture condition.(3)Nitrification and denitrification rate in the treatment group with 40%WHC end point are positively correlated with the antecedent soil moisture content.When the soil moisture is 80%WHC-80%WHC,nitrification rate and AOB amoA gene abundance are both highest prove that AOB is the dominant microorganism of nitrification.Antecedent soil moisture content have no significant effect on nirS gene,but nosZ gene abundance could reflect the intensity of denitrification.When the soil moisture is 40%WHC-80%WHC,nosZ gene has the largest increase,the denitrification rate is high,and the N2O flux is the highest.Denitrification is more complete and N2O emissions are reduced under 60%-80%WHC and 80%-80%WHC treatment. |
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