| Machilus pauhoi,with a beautiful appearance,a wide range of use and high economic value,is a precious fast-growing native broad-leaved species in the subtropical areas.In the planting of M.pauhoiis,how to accurately formulate the nutrient addition scheme is of paramount importance in efficiently cultivation of the seedings and the artificial forest.Nitrogen is one of the important elements affecting growth and development of plants.Nitrate nitrogen and ammonium nitrogen are the main inorganic nitrogen forms that plants can absorb directly.However,the preferences in the absorption and utilization of different plants for nitrate nitrogen and ammonium nitrogen are different.Therefore,application scheme of nitrate nitrogen and ammonium nitrogen can not only save resources,but also promote the growth of plant.In this study,in order to learn about the effects of nitrate and ammonium nitrogen on the fine-root traits of M.pauhoi,the nutrients of soil and its structure of microbial community,and to apply the study result to the cultivation of M.pauhoi seedlings(forests),the M.pauhoi was taken as the experimental subject to be cultivated in red soil limited by phosphorus in the mountain of experimental area.In this study,two control groups(CKI without any nutrient,and CK2 with phosphorus only)and five combined fertilization of ammonium and nitrate nitrogen in different ratios were set up to carry out nutrient controlled experiment for two consecutive years(five ratios of combined fertilization were T1(1:9),T2(3:7),T3(5:5),T4(7:3),and T5(9:1),where the equal amounts of phosphorus as CK2 was added).The whole plants of each treamtments were sampled to measure the biomass of each organ,the main phenotypic and nutrient traits of fine roots,and the main nutrient as well as the microbial community structure of soil.After the analysis,this study preliminarrly revealed the response mechanism of fine root traits and soil microbial communitry structure of M.pauhoi to different ratio of combined fertilization of ammonium and nitrate nitrogen.The major findings are as follows:(1)The soil phosphorus content was significantly higher than that in the CK1 treatment under CK2,T2,T3,T4 and T5 treatments(P<0.05),and the soil phosphorus content was the lowest at the T1 treatment and the highest at the T5 treatment.Compared to CK1 treatment,soil carbon-nitrogen ratio were distinctly lower under the treatment of T5(P<0.05).The soil carbon-phosphorus ratio and nitrogen-phosphorus ratio were significantly lower than those in the CK1 treatment under the CK2 treatment and the combined addition of ammonium nitrogen and nitrate nigtrogen(P<0.05).Among different supply ratios of ammonium and nitrate nitrogen treatments,soil carbon-phorsphorus ratio was lowest at T5 treatment,and nitrogen-phosphrus ratio was lowest under T1 treatment.The combined fertilizaiton of ammonium and nitrate nitrogen remarkbly increased the soil nitrate nitrogen content as well as ammonium nitrogen content(P<0.05),and the soil nitrate nitrogen and ammonium nitrogen content were the highest under T5 treatment and lowest under T1 treatment.(2)The richness and diversity of soil bacteria and fungi significantly decreased under the combined addition of ammonium nitrogen and nitrate nitrogen(P<0.05).The combined fertilization of ammonium and nitrate nitrogen significantly changed the soil bacterial and fungal community structures(P<0.05).Under the T1 treatment,the relative abundance of oligotrophic and disease-causing soil microbes were higher in soil,while the relative abundance of eutrophic and disease-suppressing soil microbes were higher in soil under T3 and T5 treatments.The change of soil bacteria community structure was mainly driven by soil nitrate and ammonium nitrogen content,and the variation of soil fungal community structure was mainly caused by soil phosphorus content,carbon-nitrogen ratio and carbon-phosphorus ratio.(3)The combined addition of ammonium and nitrate nitrogen led to a significant reduction of the phosphorus content and carbon-nitrogen ratio of fine roots of four orders(P<0.05),and a significant increase of the nitrogen-phosphorus ratio of fine roots of four orders(P<0.05).Among different supply ratios of ammonium and nitrate nitrogen treaments,the carbon and nitrogen content of fine roots of four orders at T1 treatment were the lowest,and the nitrogen content of fine roots of four orders at T4 and T5 treatments were higher.The carbon-nitrogen ratio of fine root of four orders were higheset at T1 treatment.The nitrogen-phosphorus ratio of fine roots of four orders were higher at T4 and T5 treatments.Principal component analysis result indicated that fine root traits shifted to the side with higher nitrogen content,nitrogenphosphorus ratio and carbon-phosphorus ratio after combined application of ammonium nitrogen and nitrate nitrogen.(4)The combined application of different ratios of ammonium nitrogen and nitrate nitrogen did not significantly change the biomass accumulation and relative growth rate of M.pauhoi(P>0.05),and the biomass accumulation and relative growth rate of the whole plant were the highest under T3 treatment.(5)The combined fertilization of ammonium and nitrate nitrogen affect the content of soil nutrients and relative abundance of dominant flora,which ultimately influences the fine root and growing performance of M.pauhoi.The results of vector fitting analysis showed that soil nutrient including ammonium nitrogen content,nitrate nitrogen content,carbon-phosphorus ratio and carbon-nitrogen ratio were the main factors that led to the change of plant traits under different fertilization treatments.The results also indicated that Proteobacteria,Firmicutes,Acidobacteriota,Myxococcota,and Gemmatimonadota are the main bacteria phylums shaping the plant traits,and Mortierellomycota,Mucoromycota and Olpidiomycota were the main fungi phylums driving the changes of plant traits.On genus level,Bacillus、 Chujaibacter、 norank＿f-＿norank＿o＿KF-JG30-C25 and norank＿f＿norank＿o＿Gaiellales are main bacteria genera that caused the changes of plant traits,and unclassified＿f＿Aspergillaceae and Metarhizium are main fungal genera that caused the changes of plant traits. |
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