Effects Of Nitrogen Addition On Soil N₂O Emission And Moso Bamboo Growth And Their Characteristics Of Ammonia-oxidizing Community

Nitrogen(N)deposition is one of the essential pathways of nitrogen input in natural ecosystems and plays a crucial role in nitrogen biogeochemical cycles.Compared with inorganic nitrogen deposition,there were few studies available on the deposition of organic nitrogen.Furthermore,previously few studies reported the effects of different nitrogen deposition on soil NH4+/N03-ratio and ammonia-oxidizing community;moreover,on the emission of N2O and the growth of Moso bamboo(Phyllostachys edulis).Two nitrogen addition simulation experiments were conducted in this study to investigate how different forms of nitrogen deposition affect soil N2O emission,bamboo growth and the characteristics of the corresponding ammonia-oxidizing microbial community.The soil from the Chinese subtropical moso bamboo forest was selected for laboratory incubation experiment.Furthermore,inorganic,organic and mixed nitrogen addition and control treatments were set to study the N2O emission and nitrogen transformation.The seedlings of P.edulis were selected for the pot experiment,and different NH4+/NO3-ratio treatments were set.Their growth and N absorption were studied by 15N isotope tracer.Combined with T-RFLP,qPCR and high-throughput sequencing,the abundance and components of ammonia-oxidizing community were analyzed to explore the role of the ammonia-oxidizing community in the response of N2O emission and bamboo growth to N addition.This study aimed to elucidate the ecological and environmental effects of soil N management in artificial forests from the perspective of soil-plant-microorganism,and provide scientific support for the sustainable ecological management of subtropical P.edulis forests.The results of incubation experiment showed that the addition of different forms of N could increase the concentration of NH4+,NO3-and water-soluble organic N in the soil,which could increase the NH4+/N01-ratio,decrease the soil pH and increase the soil N2O emission.The addition of inorganic N mainly promoted nitrification,and the NH4+/NO3-ratio and N2O emission increased by 173.0%and 97.4%,respectively.The addition of organic N mainly promoted ammonification,and the NH4+/NO3-ratio and N2O emission increased by 475.1%and 27.1%,respectively,but the emission peak appeared later.Compared with inorganic N treatment,the N2O emission and soil acidification caused by N addition could be alleviated.In the mixed treatment of organic and inorganic N,soil NH4+/NO3-ratio and N2O emission increased by 245.0%and 46.1%,respectively.The ammonia-oxidizing archaea(AOA)community formed by N addition was different from the CK treatment,and the ammonia-oxidizing bacteria(AOB)community formed by N addition treatment with different forms.The results of pot experiment showed that the high NH4+/NO3-ratio promoted the growth of P.edulis.Planting P.edulis could maintain the high NH4+/NO3-ratio(3.20±0.13)in the soil by inhibiting nitrification and uptaking more NO3-,which was beneficial to its growth.The AOA may play an important role in the response of the soil planted with P.edulis to different ratio of NH4+/NO3-addition,and the high ratio of NH4+/NO3-addition formed a distinct AOA community as compared to other treatments.In conclusion,the addition of inorganic N can promote the conversion of soil N quickly than the addition of organic N and thus promote the emission of N2O.The addition of organic N can promote the increase of soil NH4+/NO3-ratio and alleviate the emission of greenhouse gases and soil acidification to a certain extent.Significant changes in NH4+/NO3-ratio could affect plant growth.A higher NH4+/NO3-ratio could promote P.edulis,and P.edulis could maintain NH4+/NO3-ratio in soil for its growth,indicating that different NH4+/NO3-ratio could regulate the productivity of P.edulis.Soil AOA communities were sensitive to N forms and different NH4+/NO3-ratios,while AOB communities were only responsive to different N forms.The abundance of AOA in different N treatments were higher than that of AOB,which confirmed that the AOA played a dominant role in ammonia oxidization in acidic soil.