Effects Of Different Fertilizer Reduction Measures On N₂O Emission And Related Microbial Communities In Rice Field

China paddy ecosystem was characterized by wide planting area and large nitrogen fertilizer input?especially nitrogen fertilizer?,where the issue of N₂O emission has caused public concern.Fertilizer reduction and partially substituting inorganic fertilizer with organic amendments were widely adopted to reduce the emission of N₂O.However,the current understanding of the effects of different organic-substitute fertilization on N₂O emission and related microbial communities in paddy field was not clear and comprehensive.To provide theoretical basis and data support for optimizing nitrogen fertilizer management,mitigating N₂O emission in rice field and clean production of rice,a six-year field trial that comprised four fertilization strategies?CF:chemical fertilizer;PM:pig manure substituting for 20%chemical N;BF:biogas slurry substituting for 20%chemical N;and GM:milk vetch substituting for 20%chemical N?and No N fertilizer application as CK,the abundance and community structure of ammonia oxidizers were examined by using qPCR and Illumina Miseq sequencing approaches based on the functional marker genes?amoA,nirK,nirS?in a low fertility paddy field.The main results obtained are as follows:1.Organic-substitute fertilization strategies were capable of maintaining the rice yield and reducing N₂O emissions.Compared with CF,rice yield in PM treatment was increased by 8.39%,while decreased by 6.65%and 1.92%in BF and GM,respectively.In the case of the cumulative N₂O emissions,PM and BF treatments decreased by 9.12%and 2.12%,while the GM treatment increased by 7.87%,respectively.Soil organic matter?SOM?,alkaline nitrogen?AN?,total nitrogen?TN?,C/N ratio?C:N?and nitrite reductase genes?nirS and nirK?abundance were significantly correlated with N₂O cumulative emissions.2.AOA was more responsive to organic-substitute strategies than AOB,while both AOA and AOB had a significant impact on soil potential nitrification rate.Compared with the CF treatment,the organic-substitute fertilization significantly increased the diversity and gene abundance of AOA,while less effect were observed on that of AOB.Both AOA and AOB gene abundance were significantly correlated with soil potential nitrification rate.3.Nitrogen application had significant effects on nirK and nirS,and nirS was more responsive to organic fertilizer.Organic-substitute fertilization increased the Shannon diversity of nirS,from which PM and GM treatments reaching the level of statistical significance?P<0.05?.Nitrogen application significantly increased the gene abundance of nirK and nirS,while only the nirS gene abundance of GM treatment was significantly higher than that of CF.Soil factors that driving the changes of abundance and structure in nirK and nirS communities were mainly affected by soil TN?AN?pH?NH₄⁺-N and MBC.The relative abundance of nirK genus was clustered clearly according to the types of nitrogen fertilizer,while the relative abundance of nirS genus was more responsive to organic-substitute fertilizations.Above all,organic fertilizer regulates N₂O emission by affecting nirK and nirS communities.Pig manure partially substituting chemical N fertilizer can not only ensure stable rice production,but also be capable of decreasing N₂O emmision in paddy field,which was the best fertilizer application measure in this experiment.