| Camellia oleifera,also known as camellia oil tree and tea seed tree,is one of the important woody oil tree species in China,mainly distributed in 16 southern provinces(regions)including Hunan,Guangxi,Jiangxi,etc.Nitrogen is one of main limiting factors of C.oleifera growth and fruiting.Understanding the transformation process of nitrogen in the rhizosphere of C.oleifera and the abundance and diversity of key microbial communities is the basis for improving the efficiency of soil nitrogen absorption and utilization by C.oleifera.In this study,the rhizosphere soil of the improved variety of C.oleifera 'Huajin' was used as the research material,and the chemical and biological properties of the rhizosphere soil of C.oleifera(Am),nitrate(Ni),and urea(Ur)were analyzed under short-term treatments.The changing law of microorganisms aims to provide certain reference materials for nitrogen management in C.oleifera forest land.The main results are as follows:(1)The chemical properties,enzyme activity,and microbial biomass carbon and nitrogen content of the rhizosphere soil of C.oleifera under different forms of nitrogen fertilizers were measured.The results showed that the three types of nitrogen fertilizers significantly reduced the pH of the rhizosphere soil of C.oleifera,and the pH of the soil treated with Ur was higher than that of Am and Ni treatments.The content of total nitrogen,alkali-hydrolyzable nitrogen and organic matter in the soil of Ur treatment for 10 d was significantly higher than that of other treatments,and the content of ammonium nitrogen,nitrate nitrogen and organic carbon at 30 days is significantly higher than other treatments.The soil protease and urease activities of Ni and Ur treatment for 10 d were significantly higher than 0 d and 30 d,while the Am treatment was the opposite;the NR activity of Ni treatment for 10 d and the NiR activity of Ur treatment for 10 d were lower than 0 d.The activities of NR and NiR treated with Am for 10 d were higher than 0 d.The soil microbial biomass carbon content of Ur and Ni treatment for 30 d was significantly higher than that of Am treatment and other times,and the microbial biomass nitrogen content of Am treatment for 10 d was significantly higher than that of other times and treatments.The mineralization rate of rhizosphere soil in Ni treatment is positive,while that in Am treatment is negative.The mineralization rate of Ur treatment is negative at 10 d and positive at 30 d.(2)Fluorescence quantification and high-throughput sequencing were used to determine the effects of different nitrogen fertilizer treatments on the abundance and diversity of nitrogen-fixing microorganisms in the rhizosphere soil of C.oleifera.The abundance of nitrogen-fixing microorganisms and Shannon,Chao 1,Ace indexes of Ur treatment for 30 d were higher than other treatments and time.The abundance of nitrogen-fixing microorganisms in Am treatment for 10 d and Chao 1,Ace index higher than 30 d and other treatments at the same time.The nitrogen-fixing microorganisms in the rhizosphere of C.oleifera are mainly ?-proteobacteria,and the dominant genus is Bradyrhizobium.LEfSe analysis found that the number of different nitrogen-fixing microorganisms was the most in the samples treated with Am for 10 d and Ur treated for 30 d.Paraburkholderia and Azospirillum are the most influential different bacteria in the samples treated with Am for 10 d and Ur treatment for 30 d,respectively.The results of RDA analysis showed that the abundance of Bradyrhizobium was positively correlated with NO3--N and C/N,while the abundance of Azospirillum was positively correlated with TN and pH.The abundance of Paraburkholderia is only positively correlated with NH4+-N.(3)The effects of different forms of nitrogen fertilizer on the abundance and diversity of ammonia oxidizing bacteria in the rhizosphere soil of C.oleifera were determined by fluorescence quantification and high-throughput sequencing.The results showed that Am and Ur treatments can significantly increase the abundance of ammonia oxidizing bacteria.The community structure of ammonia oxidizing bacteria in the rhizosphere soil of C.oleifera is relatively simple,mainly ?-proteobacteria,and the dominant genus that can be identified is Nitrosospira.The Chao 1 and Ace indexes of ammonia oxidizing bacteria treated with Am for 10 d and Ur treated for 30 d were higher than other times.The results of LEfSe analysis showed that Nitrosospira briensis was a marker species in the samples treated with Ur for 30 d;the results of RDA analysis showed that TN,TOC and the abundance of Nitrosospira were positively correlated.(4)Fluorescence quantification and high-throughput sequencing were used to determine the effects of different forms of nitrogen fertilizer on the abundance and diversity of denitrifying bacteria in the rhizosphere soil of C.oleifera.The results show that:in 3 time periods,the abundance of nirK-type denitrifying bacteria treated with Ni and Ur was significantly lower than that of Am treatment,and the abundance of nosZ-type denitrifying bacteria was significantly higher than that of Am treatment at 30 d.The Shannon,Chao 1 and Ace indexes of denitrifying bacteria treated with Am for 10 d were significantly higher than other times,while the indexes of Shannon,Chao 1 and Ace of denitrifying bacteria treated with Ur for 30 d were significantly higher than that of 10 d.Bradyrhizobium and Achromobacter are the dominant genus of nirK and nosZ denitrifying bacteria,respectively.LEfSe analysis found that the number of different denitrifying bacteria in the samples treated with Am for 10 d and Ur treatment for 30 d was higher than that of other nitrogen fertilizers at the same time.Among the nirK-type denitrifying bacteria,Bosea and Nitrosospira were the most influential different bacteria in the samples treated with Ur for 30 d and Am treated for 10 d,respectively.Neisseria is the most influential genus of nosZ denitrifying bacteria treated with Ur for 30 d.RDA analysis showed that the abundance of and were positively correlated with TN and pH.The abundance of Achromobacter is positively correlated with NO3--N and C/N,while the abundance of Bradyrhizobium is positively correlated with TOC,AN,NO3--N and C/N.The abundance of Neisseria is positively correlated with TOC,AN,NO3--N,C/N.The review shows that the application of different forms of nitrogen fertilizer not only affects the chemical properties,enzyme activities and microbial biomass carbon and nitrogen of the rhizosphere soil of C.oleifera,and also has an impact on the nitrogen cycle microbial community.For C.oleifera under the experimental conditions,urea and ammonium nitrogen fertilizer can increase the abundance and community diversity of nitrogen cycle microorganisms in rhizosphere soil more than nitrate nitrogen fertilizer. |
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