Effects Of Different Fertilization Treatments On Microbial Nitrification And Denitrification In Rhizosphere Soils In Subtropical Red Soils

Single fertilization not only damages the soil structure and leads to the decline of land productivity,but also brings a series of environmental problems,including undergroud water pollution,and greenhouse gas?N₂O?emission.And unreasonable application of organic fertilizer will also cause adverse effects on plant growth and soil environment.Reasonable mixing application of chemical fertilizer and organic fertilizer is favorable to increase soil fertility,improve soil environment,enhance microbial activity,and influence elements transformation,which is an effective way to establish sustainable agricultural development.Nitrification and denitrification are the main processes of nitrogen cycle and also important ways of nitrogen loss in soil.The effects of the patterns of chemical fertilizer and organic fertilizer mixing application on soil nitrifying and denitrifying microbes is still unclear.In this study,subtropical red upland soil developed from quaternary red clay under differentfertilizationtreatmentswereselected.Q-pcrand high-throughput sequencing were used todetermine the abundance and community composition structures of nitrifiers and denitrifiers in rhizosphere and non-rhizosphere soils.The research results are as follows:?1?The roots significantly reduced the content of NH₄⁺-N and NO₃^--N in the rhizosphere soil,whereas promoted the accumulation of DOC in the rhizosphere.However,fertilization methods also significantly changed the physicochemical properties of soil.With the application of organic fertilizer,the content of NH₄⁺-N decreased,while the content of NO₃^--N and DOC increased slightly,and the content were highest in F2treatment.On the contrary,the aboveground biomass was the lowest in F2 treatment.Correlation analysis showed that aboveground biomass was significantly negatively correlated with soil NO₃^--N and DOC.?2?The roots suppressed soil nitrification potential?PNA?at a certaindegree,butthedifferencebetweenrhizosphereand non-rhizosphere was not significant,however,the difference between different fertilization treatments was significant.The effect of roots on soil nitrification microorganism was only reflected in the improvement of the abundance of AOA.Nevertheless,the abundance and community structure of AOA and AOB were significantly different among different fertilization treatments.Fertilization treatment mainly affected the abundance and community structure of AOA and AOB by affecting the content of soil DOC.By analyzing the relationship between the abundance and community structure of AOA and AOB with aboveground biomass and soil PNA,it was found that the abundance and community structure of AOA were significantly correlated with aboveground biomass,but not with nitrification potential.However,AOB was opposite,which is significantly correlated with PNA while has no significant correlation with aboveground biomass.The results indicated that soil PNA was mainly regulated by AOB and biomass was more related to AOA.?3?The roots stimulated the soil denitrification potential?PDA?to some extent,but with different fertilization treatments,the difference of PDA between rhizosphere and non-rhizosphere soil was different.Although the roots can promoted the abundance of nirK and nirS genes,there was no significant difference between rhizosphere and non-rhizosphere,however,there was significant difference between different fertilization treatments.As to denitrifying microbial community,there wassignificant correlation between the PDA and nirK-containing denitrifying community,while there was significant correlation between nirS-containing denitrifying community with aboveground biomass.This indicated that the PDA of soil was mainly affected by the microorganisms with nirK gene,while the aboveground biomass was more sensitive to the microorganisms with nirS gene.