| Nitrif ication is an important process in the nitrogen(N)cycle.Both substrates and final products of nitrification are important sources for the growth of microorganisms and crops,however,the denitrif ication process or the anaerobic ammonia oxidation process will cause the volatilization of nitrogen(N2)or the leaching of nitrate and lead to N losses.Therefore,the study of nitrification is of great signif icance for improving the utilization of nitrogen fertilizer and reducing the loss of nitrogen.The classic nitrification process is a two-step process completed by the cooperation of ammonia-oxidizing microbes(Ammonia-oxidizing archaea,AOA and Ammonia-oxidizing bacteria,AOB)and nitr ite-oxidizing bacteria(NOB).In 2015,it was discovered that certain species belonging to Nitrospira in the nitrite oxidizing bacteria(NOB)can directly oxidize ammonia to nitrate,which was defined as complete ammonia oxidizers(comammox);AOA,AOB,which can oxidize ammonia to nitrite,and NOB,which can only oxidize nitrite,can be named“incomlplete nitrifers”.The purpose of this article is to investigate the effects of soil utilization and management patterns on the activity and community structure of complete nitrifers and incomlplete nitr ifers.Firstly,soil nitrification potential(PN)and nitrite oxidation potential(PNO)were used to characterize the activities of AOA,AOB,comammox and NOB for paddy field,upland and forest soils developed from two parent materials(red soil and purple soil).The abundance of six functional genes were determined by real-time PCR(qPCR).The community structure composition of AOA,AOB and NOB was analyzed by high-throughput sequencing,and the community structure composition of comammox Nitrospira was analyzed by clone sequencing.Secondly,the cultivated land,fallow land and forest land of different soil types(Jilin black soil,Zhengzhou fluvo soil,Shanxi loess,Chongqing purple soil and Hunan red soil)were selected to study soil nitr ifying microbial activity,abundance and community structure.Thirdly,red soils with different fallow years managements were selected to study fallow effects on soil nitr ifying microbial activity,abundance and community structure.The main research results are as follows:(1)The soil nitrif ication potential(PN)of red soils and purple soils were 0.11?0.37?g NO3--N g-1 dry soil h-1 and 0.18?0.46?g NO3--N g-1 dry soil h-1,respectively.The nitrite oxidation potential(PNO)of red soil and purple soil were 0.13?0.86?g NO2--N g-1 dry soil h-1 and 0.44?1.46?g NO2--N g-1 dry soil h-1,respectively.The maximum value of soil PN and PNO appeared in paddy soil,and the minimum value appeared in forest soil,the difference was significant(P<0.05).The PN and PNO in purple soil were higher than those in red soil,indicating that the environment of neutral paddy soil was more conducive to the occurrence of soil nitr ification.The abundance of AOB amoA gene in paddy soil,upland soil and forest soil developed from red soil was 3.32×106,2.76×106 and1.74×105 copies g-1 dry soil,respectively.The abundance of AOB amoA gene in paddy soil,upland soil and forest soil developed from purple soil was 1.38×107,3.02×106,and 3.60×105 copies g-1 dry soil.The results showed that the abundance of AOB in paddy soil was higher than that in upland soil and forest soil,which may be the main promoter of nitrification in neutral paddy soil.The AOA/AOB ratio was signif icantly affected by soil utilization.The AOA/AOB ratio of forest soil was higher than that of paddy soil and upland soil,but there was no significant difference in the AOA/AOB ratio between upland and paddy field soil.Based on the AOA and AOB community diversity indexes,it is found that the AOB community diversity of upland soil was higher than that of paddy soil,and the AOA community diversity of forest soil was higher than that of paddy soil.This showed that AOA has more survival advantages in forest soil.The abundance of nxr A gene in paddy soil and upland soil was significantly higher than that in forest soil(P<0.05).The highest abundance of nxr B gene in purple soil was found in forest treatment(4.19×107 copies g-1 dry soil),and the abundance of nxr B gene in forest soil in red soil was higher than that of nxr A gene.The study found that the nxr B/nxr A ratio in forest soil was higher than that in paddy and upland soils.Based on the NOB's nxr A and nxr B community diversity index,it was found that the Nitrobacter nxr A community diversity in paddy and dry land was higher than that in forest land soil.These results indicated that Nitrospira is suitable for growing in forest soil,while Nitrobacter is more suitable for growing in paddy fields and upland soils.The higher abundance of comammox was detected in paddy soil,and the abundance of comammox clade A amoA gene in upland soil and forest soil was higher than that of comammox clade B.High-throughput sequencing results showed that the main AOB in paddy soils developed from purple soils was Nitrosospira(86.5%),while the AOB in upland soils mainly included Nitrosospira(53.1%),Nitrosovibrio(19.5%)and Nitrosomonas(15.2%),which showed that soil utilization has a signif icant impact on the composition of the AOB community.The NOB in paddy f ield and upland soil was mainly Nitrobacter-like NOB,the forest soil developed from purple soil was mainly Nit rospi ra-like NOB,and the forest soil developed from red soil contained Nitrospira(5.3%),Desulfuromonas(4.5%)and Nitrosococcus(4%),but Nitrospira was still the main NOB.The cloning and sequencing results showed that the comammox in the paddy soil developed from red soil was mainly composed of Nitrospira inopinata and Nitrospira nitrosa species,while the comammox in paddy soil developed from purple soil was mainly Nitrospira inopinata,and the comammox in upland soil was mainly Nitrospira inopinata.(2)The nitrification potential(PN)and nitrite oxidation potential(PNO)of cultivated land was signif icantly higher than that of fallow land and forest land.The PN of fluvial soil in Henan was the highest,which was 1.26?g NO3--N g-1 dry soil.The study found that the soil nitrif ication potential(PN)decreased significantly after 30 years of fallow and the PN of forest soil reached the lowest value.Compared with the cultivated land of Jilin black soil,Henan fluvo-aquic soil,Shanxi loess soil,Chongqing purple soil and Hunan red soil,the nitr ification potential(PN)of fallow soil were decreased by 15.88%,39.55%,45.36%,30.66%and 53.15%,respectively.Further analysis found that with the increase of fallow years,the nitrification potential(PN)and nitrite oxidation potential(PNO)showed a downward trend,and the soil nitr ification potential(PN)and nitrite oxidation potential(PNO)of the 0 year fallow soil were 0.37?g NO3--N g-1 dry soil and 0.86?g NO2--N g-1dry soil,respectively.These research results indicated that the soil nitr ification activity decreases after 30 years of fallow.qPCR analysis showed that the abundance of the AOB amoA gene in fallow land was significantly lower than that in cultivated land(P<0.05),which was lower by 73.3%,77.4%,79.1%,83.69%and 94.56%,respectively.The abundance of the AOA amoA gene in the fallow land of Jilin black soil and the fluvo-aquic soil of Henan increased signif icantly,the abundance of the AOB amoA gene in the fallow land of Shaanxi loess and Chongqing purple soil was significantly reduced(P<0.05).The abundance of AOB amoA gene in fallow soil of Hunan red soil was 2 orders of magnitude lower than that of AOA amoA gene,which indicatesd that the soil affects the abundance of AOA and AOB after 30 years of fallow.With the increase of fallow years,the abundance of AOB amoA gene decreased successively,while there was no significant difference between the abundance of AOB amoA gene in 3,11 and 30 years of fallow,and the abundance of AOB amoA gene in fallow of 30 years was the lowest.The ratio of AOA/AOB gene abundance increased with the increase of fallow years,which indicated that fallow years affect the abundance of soil AOA and AOB,and AOA may be the main promoter of nitrification in fallow soils.The nxr B/nxr A ratios of different soil types after 30 years of fallow were higher than that of cultivated soils,and the nxr B/nxr A ratios of soils of 0,3,11,and 30 years of fallow increased sequentially,which indicated that the Nitrospira was suitable for fallow land.The abundance of comammox clade A amoA gene in fallow soil of Jilin black soil,Henan f luvo-aquic soil and Hunan red soil was lower than that in cultivated soil,while the abundance of comammox clade B amoA gene was higher than that in cultivated soil,which was 26.66%,27.83%and 98.46%higher,respectively.However,the abundance of the comammox clade A amoA gene in the cultivated land,fallow land and forest soil of Shaanxi loess and Chongqing purp le soil increased sequentially,while the abundance of comammox clade B amoA gene decreased sequentially.Except for red soil forest land,with the increase of fallow years,the abundance of comammox clade B amoA functional genes increased sequentially.The results of metagenomics sequencing indicated that AOA was mainly Nitrososphaera.Compared with cultivated land,the soil of different soil types after 30 years of fallow affects the proportion of Nitrosospira and Nitrosococcus of AOB.The dominant species of NOB was Nitrospira.With the increase of fallow years,NOB may affect the community structure composition.Based on these results,concluded as follows:(1)Soil utilization pattern significantly affected the aboundances of complete ammonia oxidizers and incomlplete nitrifers.The aboundance of comammox clade A,AOB and Nitrobacter-like NOB in paddy soil was higher than these in forest soils,while the amount of AOA and Nitrobacter-like NOB in forest soil was higher than in paddies.Nitrospira-like NOB was the dominant NOB in forest soil;(2)Soil utilization signif icantly affected the community structure of complete ammonia oxidizers and incomlplete nitrifers.The main AOB in the paddy soil developed from purple soil was Nitrosospira,while the AOB in upland soil mainly were Nitrosospira,Nitrosovibrio and Nitrosomonas.The NOB in paddy field and upland soil were mainly Nitrobacter-like NOB,and forest soil was mainly Nitrospira-like NOB.The comammox in the paddy soil developed from red soil was mainly composed of Nitrospira inopinata and Nitrospira nitrosa,while the comammox in the paddy soil developed from purple soil was mainly Nitrospira inopinata,and the comammox in upland soil was mainly Nit rospira inopinata;(3)Fallow management significantly affected the number of complete ammonia oxidizers and incomlplete nitrifers.The number of AOA in fallow soil was higher than that of AOB,and the number of Nitrospira-like NOB was higher than that of Nitrobacter-like NOB.The effects of fallow on the number of complete ammonia oxidizers and incomlplete nitr ifers depended on soil types.(4)The fallow management patterns significantly affects the community structure of complete ammonia oxidizers and incomlplete nitr ifers,and the fallow soil affects the proportion of Nitrosospira and Nitrosococcus of AOB.The dominant species of NOB in fallow land was Nitrospira. |
PDF Full Text Request