Study On Community Structure Of Nitrifiers And Denitrifiers In Soil Of Different Habitats

The Loess Plateau and Tibet Plateau are the two major terrestrial ecosystems in China.In recent years,human and natural disturbances have been attributed to the serious soil erosion in the Loess Plateau and the severe degradation of the main vegetation in the Tibet Plateau.Because nitrogen is the main nutrient elements in the biosphere,habitats' destruction has also led to the imbalance of the nitrogen cycle.Meanwhile,nitrous oxide produced by nitrification and denitrification,is the direct source of greenhouse gases,causing the global temperature to rising year by year.Therefore,the research of nitrification and denitrification can provide theoritical support to predict climatic change,be sustainable management and recover barren land in The Loess Plateau and Tibet Plateau.Although the study of nitrification and denitrification are more in different ecosystems,it understood poorly between soil of different habitats.In order to explore the response soil type and soil properties to nitrifiers and denitrifiers,we investigated the abundance and community structure of nitrifiers and denitrifiers by the combination of clone library analysis and quantitative polymerase clain reaction(qPCR)in three types of soil(agricultural soil,alphine meadow soil,wetland soil)of different habitats.The results are as follows:1.The study of abundance of nitrifiers and denitrifiers in soil of different habitatsThe results of real-time(qPCR)assays showed that abundances of nitrifiers and denitrifiers are greatly significant(p<0.05).The abundances of Ammonia-oxidizing archaea(AOA)and Ammonia-oxidizing bacteria(AOB)amoA gene copies ranged from 2.1× 107 to1.7×109 copies g-1 dry soil and 7.7×105?1.6×108 copies g-1 dry soil,respectively.The abundance of AOA amoA gene copies in alphine meadow soil was about 80 fold in agricultural and wetland soil,respectively,and the abundance of AOB amoA gene copies in agricultural soil was respectively 211.8 and 14.1 fold in wetland and alphine meadow soil,while only in the agricultural soil the abundance of AOB was higher than AOA and was 7.3 fold in AOA.The abundance of nirK gene in the alphine meadow soil was respectively 11.8 and 69.2 fold in the agricultural and wetland soil,ranging from 2.1×105 to1.4×107 copies g-1 dry soil.2.Relationship between the abundance of nitrifiers and denitrifiers and environmental factorsPearson's correlation analysis revealed that no significant relationships were obtained between the abundance of AOA amoA gene and nirK gene and environmental variables detected in this paper(p>0.05).The abundance of AOB amoA gene was negative correlation with soil moisture(r=-0.716,p<0.05),whereas it was positive correlation with NO3-(r=0.928,p<0.01).3.The effect of soil propertis on nitrifiers and denitrifiers community structureThe results of CCA analysis showed that pH and NO3-=N had significant effects on the community structure of AOA and AOB in the agricultural soil.In the wetland soil,soil moisture,NH4+-N and total nitrogen were main factors for the changes of AOA and AOB community structure.Changes of the AOA and AOB community structure had no signifiant correlation to environmental factors in the alphine meadow soil(p>0.05).Change of the nirK community structure with environmental factors was consistent with changes of the AOA and AOB community structure in three soil.In conclusion,nitrifiers and denitrifiers community composition and abundance had significant differences between soil of different habitats.No signifiant relationships were obtained between the abundance of AOA amoA gene and nirK gene and environmental variables detected in this paper,whereas soil moisture and NO3-N were main factors for the abundance of the AOB amoA gene.Differences of nitrifiers and denitrifiers community structure were caused by soil properties between soil of different habitats.