Effects Of Reducing Chemical Fertilizers On Carbon And Nitrogen Dynamics And The Abundance Of Related Functional Microorganisms In Soil Profile Of Paddy Fields

Excessive or unreasonable use of chemical fertilizers in farmland management has become one of the important sources of non-point source pollution,which is bound to threaten agricultural environmental health.Based on a long-term plot experiment in southern Jiangsu Province,this paper studied the distribution of carbon and nitrogen elements in soil profile of paddy field under the measures of replacing chemical fertilizer with organic fertilizer and rice-dynamics rotation for weight loss,and the effects on the abundance of carbon and nitrogen transforming microbial community.Through this study,it is expected to clarify the dynamics of carbon and nitrogen elements and the functional microorganisms that drive their transformation in soil profiles under different weight loss measures,and reveal the main controlling environmental factors that affect the abundance of microbial communities for carbon and nitrogen transformation in soil profiles.This study can provide theoretical support and scientific basis for clarifying that organic fertilizer replaces chemical fertilizer and dynamics planting can reduce soil carbon fixation and regulate soil profile nitrogen loss in paddy fields.The key conclusions of this research are summarized as follows:1)Applying organic fertilizer increased the contents of TN（total nitrogen）,AN（alkaline hydrolysis nitrogen）and DOC（dissolved organic carbon）in 0-20 cm soil of paddy field.In 20-40 cm and 40-60 cm soil depths,The contents of TN,AN and DOC in soil treated with organic fertilizer were lower than those treated with conventional chemical fertilizer,which reduced the leaching of carbon and nitrogen elements downward.The rice-milk vetch rotation increased the contents of DOC,TN,NO₃^--N（nitrate nitrogen）and NH₄⁺-N（ammonium nitrogen）in soil profile,In addition,the effect of reducing fertilization on the contents of DOC,TN,NO₃^--N and NH₄⁺-N in soil profile was especially significant.2)The substitution of organic fertilizers for chemical fertilizers could increase the abundance of carbon fixing genes（cbb L、cbb M、acc A、puf M）,carbon decomposing genes（GH48、chi A、cbh I）,nitrogen fixing gene（nif H）and nitrifying genes（AOA、AOB）in 0-20 cm soil of paddy field.With the depth increases,the abundance of functional genes for carbon and nitrogen transformation showed a decreasing trend,the abundance of denitrifying genes in 20-40 cm and 40-60 cm soil depths tended to decrease with the application increasing of organic fertilizer,it was consistent with the variation trend of carbon and nitrogen elements in soil profile.The abundance of genes was almost significantly correlated with NH₄⁺-N,NO₃^--N,DOC,TN,SOM,AN and TP（P<0.01）.3)Rice-milk vetch rotation increased the gene abundance of Carbon fixation（cbb L、puf M）,nitrogen fixation gene（nif H）and nitrification function genes（AOA、AOB）in the 0-20 cm soils.At the same time,in the 20-40 cm and 40-60 cm soil layers,The abundance of gene of carbon and nitrogen transformation function showed that reduced fertilization was higher than conventional fertilization,this is consistent with the distribution of carbon and nitrogen elements in soil profile.Correlation analysis showed that the abundance of functional genes for carbon and nitrogen transformation was almost correlated with NH₄⁺-N,NO₃^--N,DOC,TN,SOM,AN and TP significantly（P<0.01）.