Study On The Effect Of Applying Straw Biochar On Denitrification And N₂O Emission In Purple Soil

N₂O is an important greenhouse gas that can cause damage to the ozone layer.A variety of non-biological mechanisms and microbial activities in the soil will produce N₂O gas.When the water filled pore space(WFPS)is greater than 70%,denitrification is the most important way of N₂O emission from paddy soil.Due to the special nature of purple soil,the risk of soil nitrogen loss and N₂O emission is particularly prominent.Biochar can change the physical and chemical properties of the soil,thereby affect the nitrification and denitrification process of the soil,and affect the emission of N₂O gas in the soil ultimately.At present,the mechanism of biochar's effect on soil N₂O emission still needs further exploration and research.In order to explore the impact and mechanism of addition of biochar on denitrification in purple soil,N₂O gas emissions and comprehensive greenhouse effect,the thesis uses rice straw as raw material to prepare three types of biochar at different pyrolysis temperatures(300,500 and 700?),mix them with soil in different addition ratios(1%and 5%),and carry out indoor culture experiments.Through research,the main conclusions are as follows:(1)The results of soil cultivation experiments showed that application of biochar increased the aeration porosity of the purple soil by 1.83%?40.57%and improved the aeration performance of the soil;the application of biochar of 300?had a certain inhibitory effect on the evaporation of water in the purple soil;the application of biochar increased the soluble organic carbon content of purple soil by 19.9%?217.6%,and increased the content of substrates that can be used by microorganisms;the application of biochar increased the initial pH value of purple soil by 0.38?1.79 units;compared with the control group,the application Straw biochar increased the fixation amount of nitrate nitrogen in the soil,and the fixation amount of nitrate nitrogen in the experimental group increased by 211.3%.(2)The results of flooding cultivation experiments showed that denitrification in purple soil conforms to the first-order reaction kinetic model.The denitrification rate constants of the 7 treatment groups under overflow conditions range from 0.067 to0.362d^-1;there is a significant negative correlation between soil pH,fixation amount of nitrate nitrogen and denitrification rate;the application of biochar increases the pH value of the purple soil and the fixed amount of nitrogen,thereby creating an alkaline environment and reducing the available nitrogen content in the soil,inhibit the process of soil denitrification eventually.(3)The measurement results of abundance of denitrification genes showed that effect of biochar application on the abundance of denitrification genes in purple soil is related to the pyrolysis temperature and the addition ratio of biochar.Biochar at 300? increased the copy number of narG gene in purple soil,while biochar at 500? had no significant effect on the copy number of narG gene,and biochar at 700? reduced the copy number of narG gene;the biochar of the three pyrolysis temperatures all increased the copy number of nirS gene in purple soil;biochar at 300? and 500? significantly increased the copy number of nirK and norB genes in purple soil,while biochar at700? had no significant effect on the two genes;most treatments significantly increased the number of nosZ gene copies in purple soil.The effect of different addition ratios on the abundance of denitrification functional genes in purple soil is:for biochar with a pyrolysis temperature of 300?,the abundance of denitrification genes in the experimental group with 1%addition ratio was significantly higher than that in the experimental group with 5%addition ratio;for the biochar with a pyrolysis temperature of 500?,the abundance levels of denitrification functional genes in the test groups with the two addition ratios are equivalent;for biochar with a pyrolysis temperature of700?,the abundance of denitrification genes in the experimental group with 5%addition ratio was significantly higher than that in the experimental group with 1%addition ratio.(4)The results of soil gas production experiments showed that application of biochar greatly reduced the emission of N₂O gas from the purple soil.The reduction rate is 44.34%?89.61%.Compared with the control group,most treatment groups reduced the comprehensive greenhouse effect of purple soil to varying degrees,and the range is between 41.91%and 94.06%.Multivariate linear regression analysis showed that the absolute content of five denitrification genes(narG,nirS,nirK,norB and nosZ)can explain 74.6%of the changes in N₂O emissions;compared to nirK and norB gene copy numbers,narG,nirS and nosZ gene copy numbers have a more important impact on N₂O emissions;structural equation models show that after biochar is pressurized into purple soil,it will affect N₂O emissions through a rather complicated mechanism.This effect is It is caused by the joint action of 10 pathways.In the regulation path of biochar on the N₂O emission of purple soil,aeration porosity and pH are more important physical and chemical factors,and the nirS gene and nosZ gene are the key denitrification genes;the addition of biochar mainly affects the abundance of nirS and nosZ genes by changing the aeration porosity and pH of the soil,and reduces N₂O emissions ultimately.