Interactive Effects Of Irrigation And Nitrogen On Nitrification And Ammonia-oxidizing Microorganisms In Greenhouse

In order to obtain high economic value,greenhouse agriculture generally has a large amount of water and nitrogen input,especially the problem of high nitrogen fertilizer input.Water and nitrogen input changes the quantity and form of nitrogen supply by affecting soil environmental conditions and related microbial activity and quantity in greenhouse production,thereby affecting the soil nitrogen transformation process and the relative contribution of ammonia-oxidizing microorganisms to nitrification.The research on the effects of water-nitrogen regulation on soil nitrification and soil ammonia oxidizing microorganisms in greenhouse has an important theoretical basis for exploring the characteristics and influencing factors for greenhouse soil under water and nitrogen regulation.Based on 8-consecutive-year field location experiments of water and nitrogen in greenhouse,the topsoil（0-20 cm）under different treatments of water and nitrogen regulation were selected.For differet soil water suction treatments of 25 k Pa（W₁）,35 k Pa（W₂）and 45k Pa（W₃）,the relative percentages of soil field water holding capacity were further used to control of different soils water（W₁:80%WHC,W₂:60%WHC and W₃:30%WHC）.Through the indoor experiment and specific acetylene inhibitor method,the experiment tried to explore the coupling effect of water-nitrogen on soil nitrification in greenhouse,soil ammonia oxidizing microorganisms（AOA,AOB）and Comammox-ammonia oxidizing bacteria（Clade A,Clade B）in greenhouse.The main results are as follows:（1）Water,nitrogen and their interaction affected the contents of ammonium nitrogen and nitrate nitrogen,the rates of autotrophic nitrification and heterotrophic nitrification and their proportion to the total nitrification rate in greenhouse soil in the microcosm incubation experiment.Autotrophic nitrification was the main pathway of 60-80%WHC,and the heterotrophic nitrification was the main of 40%WHC.Water nitrogen coupling made the autotrophic nitrification rate of W₁N₃treatment the highest,while the heterotrophic nitrification rate of W₃N₃treatment the highest.Both autotrophic nitrifying microorganisms AOA and AOB have a significant positive correlation with autotrophic nitrification rate and,AOB has a higher correlation with autotrophic nitrification rate,AOB contributes more to autotrophic nitrification.（2）The gene abundance of AOA was significantly higher than that of AOB under different water and nitrogen regulation in greenhouse,and the abundance values of both AOA and AOB were higher than those of the comannox ammonia-oxidizing bacteria Clade A and Clade B.Except for W₃N₁,W₃N₂and W₃N₃,clade A was the mian comannox ammonia-oxidizing bacteria.The effects of water,nitrogen and their interaction on the abundance of AOA,AOB and comammox Clade A were extremely significant,while water only had a very significant effect on the Clade B（P<0.01）.Both water and their interaction significantly affected the nitrification potential of greenhouse soil.Correlation analysis results showed that the soil nitrification potential was significantly positively correlated with the abundance of AOB gene in AOA,and the correlation with AOB gene was higher,indicating that AOB and AOA played a role in soil ammonia oxidation in greenhouse,and AOB may be the main contributor.Comammox Clade B showed extremely significant positive correlation with p H and NH₄⁺-N,respectively.The Comammox ammonia oxidizing bacteria Clade B liked high p H environment and had a higher affinity for ammonia.（3）Water,nitrogen and their interaction all affected the relative contribution of ammonia oxidizing bacteria（AOB）and ammonia oxidizing archaea（AOA）to varying degrees.They all contributed to the nitrification,while AOB to the nitrification in a varying degree,with AOB playing a leading role.The nitrification potential driven by ammonia oxidizing bacteria and oxidizing archaea was significantly negatively correlated with p H.NH₄⁺-N was negatively correlated with ammonia oxidizing bacteria.Under W₃water treatment,the nitrification potential driven by ammonia-oxidizing bacteria and ammonia-oxidizing archaea was less than that of W₁and W₂water treatment.In conclusion,the autotrophic and heterotrophic nitrification pathways existed simultaneously in greenhouse soil regulated by water and nitrogen,and autotrophic nitrification was the main nitrification pathway;Autotrophic nitrifying microorganisms AOA and AOB jointly drive autotrophic nitrification,and AOB played a leading role in the contribution of autotrophic nitrification.The ammonia oxidizing microorganisms in greenhouse soil regulated by water and nitrogen indicated ammonia oxidizing archaea（P<0.05）>ammonia oxidizing bacteria>gene abundance of Clade A and Clade B of Comammox ammonia oxidizing bacteria.