The Effect Of Long-time No Application Of Phosphorus On Greenhouse Gas Emission From Paddy Fields And Its Mechanisms

Phosphorus fertilization strategy of few or no in rice season and more in wheat season can increase the use efficiency of P and reduce the P loss through runoff and leaching effectively.However,CH₄ emission of no P fertilizer in rice season found increased 33-40%when compared with those with P fertilizer.Does this phenomenon exist widely?For this reason,this research uses two long-term location test plots with different soil types:Suzhou（yellow soil,started in 1980）and Yixing（hubai soil,started in 2010）as the research objects.Select the corresponding phosphorus and non-phosphorus treatments,dynamic monitoring of greenhouse gas emissions during the rice season,and simultaneous determination of the soil physical and chemical properties during the key growth period of rice and the microbial community structure related to methane emissions.Research indicates:1.The emission laws of CH₄ and N₂O in the two experimental fields are as follows:the CH₄ emission fluxes of the two experimental fields all have emission peaks about 20days after rice transplantation,and the emission peaks of NK treatment are higher than those of NPK treatment.Regarding N₂O,NPK and NK treatments in the Suzhou experimental field have significant emissions of N₂O during the rice tillering stage,and the emission value of NK treatment is higher than that of NPK treatment.The peak of N₂O emission flux in Yixing experimental field only appeared in NK treatment.2.Compared with normal phosphorus application treatment,long-term no phosphorus application treatment significantly promoted CH₄ and N₂O emissions from rice fields（P<0.05）.Taking the data of 2019 as an example,the CH₄ and N₂O emissions from NK treatment in the Suzhou experimental field were 177.35kg·ha^-1 and 0.09kg·ha^-1,which are 57%and 25%higher than NPK treatment of CH₄ and N₂O emissions,respectively.The emissions of CH₄ and N₂O treated by NK in the Yixing experimental field were 124.58kg·ha^-1 and 1.05kg·ha^-1,respectively,which were 221%and 70%higher than the emissions of CH₄ and N₂O treated by NPK.CH₄ emissions play a leading role in the greenhouse effect,contributing 94%-99%to the global warming potential（GWP）, MECHANISMS and the GWP of the two test plots without phosphorus treatment is greater than that of phosphorus treatment.3.Long-term non-application of phosphorus reduces soil available phosphorus content,organic acid content and soluble organic carbon content.These factors are closely related to CH₄ emissions,especially the soil available phosphorus content and CH4 emissions are significantly negatively correlated（correlation coefficient r=-0.987）,P<0.05).4.Compared with the normal phosphorus application,the long-term non-phosphorus treatment increased the abundance of the methanogen functional gene（mcr A）,but decreased the pmo A gene abundance,and the two rules were consistent.Among them,the mcr A gene abundance in the Suzhou test field was increased by 59.2%,146.2%,and 44.2%without phosphorus treatment at the tillering,heading,and maturity stages,respectively,and the difference in heading period reached a significant level（P<0.05）;the mcr A gene abundance in the three periods in the Yixing test field The degrees increased by 446.7%,30.8%,and 115.2%respectively,and the differences between the two treatments at the tillering stage and the mature stage reached a significant level（P<0.05）.The pmo A gene abundance of the three periods in the Suzhou experimental field decreased by 13.7%,9.2%,and 172.9%,respectively,and the difference in the mature period was significant（P<0.05）;the pmo A gene abundance in the three periods of the Yixing experimental field decreased by 34.7%,33.4%,and 40.3%,respectively.5.Under the condition of long-term non-phosphorus application,the community diversity of methanogens and methanotrophic bacteria in paddy soil and the relative abundance of dominant bacterial communities changed:the soil methanogens diversity of soil methanogens in the Yixing test field was significantly lower than that of the application of phosphorus without applying phosphorus at the tillering stage.Phosphorus treatment（P<0.05）;The relative abundance of Methylocystis,the dominant group of methanooxidizing bacteria in the Suzhou test field,in the same period without phosphorus treatment was significantly lower than that of phosphorus treatment,and the difference reached a significant level（P<0.05）.Inferred from the above,long-term non-phosphorus treatment can increase the abundance of methanogens in the soil and reduce the gene abundance of methanogens by reducing the content of soil organic acid,soluble organic carbon and soil available phosphorus,while also reducing the abundance of methanogens and methanogens.The diversity of methanotrophic bacteria and the relative abundance of their dominant flora have led to an increase in CH₄ emissions from rice fields.Inferred from the above,long-term non-phosphorus treatment can increase the abundance of methanogens in the soil and reduce the gene abundance of methanogens by reducing the content of soil organic acid,soluble organic carbon and soil available phosphorus,while also reducing the abundance of methanogens and methanogens.The diversity of methanotrophic bacteria and the relative abundance of their dominant flora have led to an increase in CH₄ emissions from rice fields.