| Camellia oleifera is an important woody oil species in China.Reasonable nutrient management is the basis of sustainable and healthy development of C.oleifera industry.N fertilizer application is one of the main measures to ensure high and stable yield of C.oleifera.In order to avoid resource waste and environmental pollution caused by unreasonable fertilization,it is the premise to understand the cycle and absorption process of different forms of N fertilizer and its microbial driving mechanism after entering C.oleifera plantation soil.Therefore,plantation and cutting seeding of C.oleifera cultivar ’huajin’ as material,the use of isotope tracer and high-throughput sequencing technologies,to research the influence of N in different forms,glycine,potassium nitrate and ammonium chloride,on N absorption efficiency of root,and on N cycle processes and microbial communities in C.oleifera bulk and rhizosphere soil.The results are as follows:(1)Response of C.oleifera root N uptake to different forms of N fertilizersThe abundance of 15N(δ15N)and nitrogen derived from fertilizer(Ndff%)of C.oleifera root were 2804‰ and 10.47%,respectively,on the 10 d after applying ammonium chloride in autumn,which were significantly higher than that in other seasons.The δ15N and Ndff%of C.oleifera root were 2118‰ and 7.90%,respectively,on the 10 d after applying potassium nitrate in summer,which were significantly higher than those in other seasons and treatments.On the 10 d after applying glycine in summer and autumn,δ15N of root were 1669‰ and 3251‰,respectively;Ndff%were 6.22%and 12.13%,respectively;They were both significantly higher than those in other seasons.The absorbed glycine molecules only accounted for 3.35%and 27.8%of Ndff%.The root δ13C were-28.42‰,-27.31‰,-11.03‰and-28.12‰,respectively,on the 10 d after applying glycine in spring,summer,autumn and winter.The soil δ13C was significantly higher than CK on 10 d after applying glycine in summer and winter.The results indicated that the N absorption efficiency and N preference of C.oleifera root was significantly different in different seasons.C.oleifera prefer nitrate nitrogen in summer while ammonium nitrogen in autumn.Although the efficiency of amino acid nitrogen fertilizer was higher in summer and autumn,only a small amount of amino acid molecules could be absorbed by the root of C.oleifera.(2)Response of soil N cycle process to different N forms in C.oleifera plantationAccording to the results of(1),in situ culture and pot experiment were used to further study the soil N cycle process in C.oleifera plantation.The results showed that the annual average net ammonification rate(AR)of C oleifera bulk soil was 0.13 mg·kg-1·d-1,and the highest in summer(0.75 mg-kg-1·d-1).The average net nitrification rate(NR)was-0.01 mg·kg-1·d-1,with no seasonal difference.The annual average AR and NR of rhizosphere soil were-0.12 mg·kg-1·d-1 and 0.20 mg·kg-1·d-1,respectively,and were both highest in autumn(0.12 mg·kg-1·d-1 and 1.39 mg·kg-1·d-1),lowest in winter(-0.39 mg·kg-1·d-1 and-0.54 mg·kg1·d-1).After fertilization,the content of alkali-hydrolyzable nitrogen increased with time in bulk soil,but it showed opposite tendency in rhizosphere soil.Applying glycine in summer could increase the net mineralization rate(MR),which was 18.66 mg·kg-1·d-1 and 1.25 mg·kg-1·d-1 of bulk and rhizosphere soil,respectively.Ammonium chloride increased AR of bulk soil in autumn(34.39 mg·kg-1·d-1)and winter(11.02 mg·kg-1·d-1),while decreased AR of rhizosphere soil in spring(-1.38 mg·kg-1·d-1)and winter(-3.21 mg·kg-1·d-1).In summer,NR of bulk soil was significantly decreased to-6.18 mg·kg-1·d-1 after applying potassium nitrate.In autumn and winter,NR of bulk soil significantly increased to 6.80 mg·kg-1·d-1 and 2.63 mg·kg-1·d-1,respectively,while that of rhizosphere soil significantly decreased to-3.45 mg·kg-1·d-1 and-3.54 mg·kg·d-1,respectively.(3)Responses of microorganisms to different N forms in C.oleifera plantation soil16S and ITS high-throughput sequencing technology,bioinformatics and soil enzyme activities were combined to analyze the dynamic changes of microbial community in C.oleifera plantation soil after applying different N fertilizers.Six dominant phyla,including Chloroflexi and Proteobacteria,and two dominant phyla,Ascomycota and Basidiomycota,were found in both C.oleifera bulk and rhizosphere soil.The acid protease activity(1330 U·g-1),nitrate reductase activity(0.861 U·g-1),the richness(Chao 1 index)of bacteria(2863)and fungi(583),and the abundance of microorganisms with nitrogen metabolism and oxidative phosphorylation functions were the highest in C.oleifera bulk soil in spring.Rhizosphere soil bacterial richness(1967)and diversity(Shannon index)(8.43)were the lowest in summer during the whole year.The abundance of denitrifying fungi in bulk soil and nitrifying and denitrifying bacteria in rhizosphere soil in autumn were higher than those in other seasons.The fungal richness and the abundance of microbial respiration and metabolism in bulk and rhizosphere soil in winter were lower than those in other seasons.Applying glycine in spring significantly increased the activity of deaminase,the abundance of ABC transporter,ammonification,nitrification,denitrification and nitrogen fixation functional bacteria in bulk soil,while decreased gram-negative bacterial,ammonification and ammoxidation functional bacterial abundance in rhizosphere soil.Fertilization in summer significantly reduced the bacterial richness and increased the abundance of microorganisms with function of nitrate reduction assimilation in bulk soil.Application of inorganic nitrogen fertilizer increased rhizosphere soil bacterial richness and diversity and the abundance of anammox microorganisms.The abundance of nitrifying and denitrifying fungi and anammox bacteria in rhizosphere soil decreased significantly when ammonium nitrogen and amino acid nitrogen fertilizer were applied in autumn.Appling nitrate nitrogen fertilizer increased the abundance of nitrifying and denitrifying bacteria in rhizosphere soil.Fertilization in winter had no significant effect on soil microbial abundance related N cycles.The results showed that the effects of N fertilizers on the N uptake of C.oleifera roots and the N cycle processes in bulk and rhizosphere soil had seasonal variations.In spring,the appropriate temperature and precipitation promote microbial activity and speed up the turnover rate of soil N.Amino acid nitrogen can promote these processes and speed up the mineralization of soil N.In summer,the root of C.oleifera had higher N absorption efficiency,and the application of amino acid nitrogen could promote N mineralization in bulk and rhizosphere soil,while the application of inorganic nitrogen fertilizer could promote the assimilation process of soil microorganisms in bulk soil and increase the abundance of anaerobic microorganisms in the rhizosphere,which reduced the efficiency of N fertilizers.The application of ammonium nitrogen and amino acid nitrogen fertilizer in autumn could not only match the ammonium nitrogen preference of C.oleifera roots,but also promote the decomposition of soil organic matter,inhibit nitrification and denitrification,and improve the efficiency of fertilization.In winter,microbial communities tend to immobilize rather than mineralize N;applying N fertilizer had no significant effect on N cycles and relevant microbial communities.In conclusion,application of amino acid nitrogen or ammonium nitrogen fertilizer in spring and autumn can meet the N demand of C.oleifera and resulting in higher ecological and economic benefits.The results provided some scientific basis for revealing the root N absorption and its regulation mechanism,and formulating rational N application scheme. |
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