Effects Of Long-term Irrigation And Fertilization Managements On Nitrogen Cycle Associated Microbes In Winter Wheat-Summer Maize Fields

The nitrogen cycling is one of the most important soil element cycles,in which nitrification and denitrification are two important processes that not only affect plant nitrogen uptake and utilization,but also lead to a series of ecological environmental issues,such as soil nitrogen loss,soil acidification and nitrous oxide(N2O)emission.Efforts devote to reveal the effects and mechanism of different fertilization and water managements on microbial communities associated with nitrification and denitrification in winter wheat-summer maize fields in the North China Plain are of great significance for regulating soil nitrogen conversion,increasing nitrogen utilization efficiency and reducing N2O emission.In the present study,soils were collected from two long-term located experiments(different N-fertilization rates and different fertilization and irrigation regimes)in the Wuqiao experimental station of China Agricultural University.Real-time PCR,T-RFLP,clone library and Illumina MiSeq sequencing were applied to investigate the abundance,diversity and community structure of nitrifiers and denitrifiers in the soils under different N-fertilization rates and different fertilization and irrigation regimes.Furthermore,potential nitrification activity(PNA)in the soils under different fertilization and irrigation regimes was also measured.The main findings are as follows:(1)There were significant differences in physical and chemical properties of the soils under different N-fertilization rates and different fertilization and irrigation regimes.Nitrogen application significantly increased soil nitrogen content,however,significantly decreased soil pH,and leaded to variations of the rest properties.Soil total nitrogen and organic carbon contents in the organic manure treated soils were significantly higher than that in the NPK treated soils.Increase in irrigation frequency significantly increased soil moisture and soil pH,and changed the rest properties in both fertilization treatments.(2)Soil PNA was in the range of 2,56?3.00 ?g NO3--N g-1·h-1 in different fertilization and irrigation regime treatments,and soil PNA was significantly positively correlated with AOB abundance.Increase in irrigation frequency increased soil PNA in the NPK treated soils,whereas decreased soil PNA in the organic manure treated soils.(3)The abundance of AOA amoA,AOB amoA,nirS and nir K genes was in the range of 3.84×108?7.78×108,8.96×106?2.66×107,1.05×10 8?4.88×108 and 4.09×107?6.50×107 copies· g-1 d.w.s in different N-fertilization rate treatments,respectively.Increase in irrigation frequency significantly increased the abundance of AOB amoA,nirS and nirK genes,whereas decreased the AOA amoA gene abundance.The abundance of AOA amoA,AOB amoA,nirS,nirK and nos Z genes was in the range of 1.92×107?1.34×109,3.46×107?7.75×107,4.46×107?1.06×109,l.56×107?7.69×107 and 2.28×108?1.63×109 copies g-1 d.w.s in different fertilization and irrigation regime treatments,respectively.Significantly higher abundance of AOA amoA,AOB amoA and nirK genes and lower abundance of nosZ gene was observed in the organic manure treated soil than that in the NPK treated soil under high irrigation frequency.Increase in irrigation frequency increased the abundance of AOA amoA,nirS,nirK and nosZ genes in both fertilizer type treatments.Increase in irrigation frequency increased the abundance of AOB amoA gene in the NPK treated soils,whereas decreased the abundance of AOB amoA gene in the organic manure treated soils.(4)There were significant differences in alpha diversity indexes of the AOA,AOB,nirS-,nirK-and nosZ-denitrifying bacterial communities.Fertilizer type significantly affected the Chaol index of the AOB,nirK-and nirK-denitrifying bacterial communities,the Shannon index of the AOB and nirK-denitrifying bacterial communities,and the ACE index of the AOB community.Irrigation frequency significantly affected the Shannon index of the AOA,AOB,nirS-and nirK-denitrifying bacterial communities,and the ACE and Chaol indexes of the AOB community.(5)There were apparent variations in community structure of the AOA,AOB,nirS-and nirK-denitrifying bacterial communities between different N-fertilization rate treatments.N-fertilization rate had a stronger effect on community structure of AOB than that of AOA,and on community structure of nirS-denitrifying bacteria than that of nirK-denitrifying bacteria,respectively.Similarly,great variations were observed in community structure of the AOA,AOB,nirS-,nirK-and nosZ-denitrifying bacterial communities between different fertilization and irrigation regime treatments.Fertilizer type had a stronger effect than irrigation regime on community structure of the AOB and nosZ-denitrifying bacterial communities,and irrigation regime had a stronger effect than fertilizer type on community structure of the AOA and nirS-denitrifying bacterial communities,and both fertilizer type and irrigation regime greatly altered the community structure of nirK-denitrifying bacteria,respectively.These results demonstrated that N-fertilization rate,fertilizer type and irrigation regime had great impacts on soil properties,and induced variations in abundance,diversity and community structure of nitrifiers and denitrifiers and soil PNA.However,N-fertilization rate,fertilizer type and irrigation regime differential affected the abundance,diversity and community structure of nitrifiers and denitrifiers,and fertilizer type and irrigation regime had different impacts on soil PNA.Our findings provide more scientific evidences for directional regulation of soil nitrogen transformation,increase in nitrogen utilization efficiency and reduction in N2O emission in the North China Plain.