Distribution Of Ammonia-oxidizers And Methanotrophs In The Different Soil Layers Of Flooded Paddy Fields

Ammonia oxidizers(AOA and AOB)are the dominant microorganisms in rate limiting step of nitrification,methanotrophs(MOB)is the dominant microorganism in rate limiting step of CH4 oxidation reaction in soil.The study found that methanotrophs and ammonia oxidizers have homologous methane monooxygenase(pmoA)and ammonia monooxygenase(amoA)methane monooxygenase,as ammonia monooxygenase reaction.In addition,the structures of CH4 and NH4+ were similar,and the competition between the two substrates and the enzyme might be competitive.However,there is not enough evidence to confirm whether there exists interaction between methanotrophs(MOB)and ammonia oxidizers(AOA and AOB).Flooded paddy fields are widely distributed in the southwest of China.The soil flooding is a layer of water,generally 3~5cm,below is a thin oxide layer,thickness is less than 1cm,then the following is the reduction of layer about 10~20 cm.The vertical depth stratification lead to differences in soil Eh value,pH value,temperature,and moisture etc..These differences will have a certain impact on microorganisms.Studying on distribution law of methanotrophs(MOB)and ammonia oxidizers(AOA and AOB)for different soil layers in flooded paddy fields is conducive to understanding the mechanism of action of microbial carbon and nitrogen cycling in the soil,to provide scientific basis forimproving soil nitrogen utilization rate and reducing greenhouse gas emissions.By using molecular techniques(PCR,qPCR,clone and sequencing),this study investigate and analyze the abundance and diversity of key functional genes,and to clarify the vertical spatial niche of methanotrophs and ammonia oxidizers.The main contents and conclusions of this study are as follows:Three sampling areas selected in this study are all in the neutral purple paddy soil area.The sampling areas were located in experimental field of Southwestern University in Beibei,Dashi Town in Hechuan District and Qingmuguan Town in Shapingba District.The soil samples of flooding(0~3 cm),the oxide layer(3~5 cm)and the reduced layer(5~20 cm)were collected.By incubation,quantitative PCR and sequencing,research on activity and community structure of methanotrophs and ammonia oxidizers in flooded paddy fields vertical depth stratification.The results show that:(1)the potential nitrification show the microbial activity of ammonia oxidizers.The results showed that potential nitrification in three kinds of flooded paddy field is Shapingba > Beibei > Hechuan.Different flooded paddy fields were detected potential nitrification of three flooded paddy fields in flooding was significantly larger than the potential nitrification of the oxide layer and reduced layer.And soil total nitrogen concentrations were positively related in different soil layers.(2)the average net rate of oxidation describe the methane oxidation capacity.The results showed the methane oxidation capacity of Shapingba paddy field is larger than Hechuan and larger than Beibei;the same trend of net methane oxidation rate in different layer between Shapingba and Hechuan flooded paddy fields: the reduced layer was significantly lower than flooding layer and oxide layer,that is the methane oxidation in flooded paddy fields is mainly completed by flooding layer and oxide layer.(3)by using those molecular techniques,the results showed that AOB amoA(AOB amoA belong to the genus Nitrosomonas)abundance and diversity Shapingba and Hechuan flooded paddy fields was significantly lower than that of AOA and MOB;AOA amoA groups had little difference,with the increase of soil depth,Group 1.1b gradually decreases,but Group 1.1a gradually increases;the diversity of MOB pmoA is much larger than the amoA gene,two species of flooded paddy fields Type I methanotrophs belonging to Methylococcacea type I methanotroph(Type Ia)and Methylocaldum(Type Ib),Type II methanotrophs for Methylocystis.With the increase of soil depth,Type I methanotrophs were enriched in the flooding layer and the oxide layer,and the Type II methanotrophs were enriched in the reducing layer.In summary,distribution of ammonia-oxidizers and methanotrophs in the different soil layers of flooded paddy fields can be attributed to the following two points:(1)ammonia oxidation and methane oxidation have certain rules;(2)the distribution of ammonia-oxidizers and methanotrophs have certain rules.