Effects Of AM Fungi On Growth,N Uptake And N Leaching Of Camellia Oleifera Seedlings Under Different N Levels

In this study,high yielding Camellia oleifera Changlin 53 was used in a pot experiment.To investigate the effects of arbuscular mycorrhizae（AM）fungi on the growth,root morphology and photosynthetic characteristics of C.oleifera under different nitrogen levels,and analyzed the optimal nitrogen level and AM fungi for the growth of C.oleifera;and we studied the effects of AM fungi on the nitrogen content,nitrogen assimilation enzyme activity and relative gene expression,and nitrogen uptake related gene expression of C.oleifera,and elucidated the mechanism of AM fungi’s effects on the nitrogen uptake metabolism of C.oleifera.At the same time,the effects of AM fungi on nitrogen content,nitrogen assimilation enzyme activity,relative gene expression and nitrogen uptake related gene expression of C.oleifera were investigated to elucidate the mechanism of AM fungi on nitrogen uptake and metabolism of C.oleifera.The results of the study can provide a theoretical basis for promoting the application of AM fungi as"microbial fertilizer"and scientific fertilization of C.oleifera seedling.The main findings are as follows:（1）Effects of inoculation with AM fungi and nitrogen application on C.oleifera growth and the optimal nitrogen level and AM fungiThe infection rate of C.etunicatum and F.mosseae of C.oleifera first increased and then decreased with the increasing nitrogen levels[0（N0）、3.75（N1）、7.5（N2）和15m M（N3）N].The plant height,root length,volume and surface area,net photosynthetic rate,and maximum photochemical efficiency of inoculated and uninoculated C.oleifera increased at first and then decreasing with increasing nitrogen levels,with a maximum at N1level;while the stem diameter showed an increasing trend.Inoculation with AM fungi had a significant effect on the plant height and stem diameter of C.oleifera.Under the condition of no nitrogen application,inoculation with C.etunicatum increased the height of C.oleifera by 14.88%compared with uninoculated plants,which was better than the treatment with F.mosseae（3.88%）;while inoculation with F.mosseae was better than inoculation with C.etunicatum after nitrogen application.At four nitrogen levels,inoculation of F.mosseae increased the root length,volume and surface area,net photosynthetic rate,maximum photochemical efficiency and actual photochemical efficiency of C.oleifera better than C.etunicatum.The result showed that compared with C.etunicatum,F.mosseae was more effective in promoting root development and enhancing photosynthesis,and N1 level was the best N level to promote root development and growth and enhance photosynthesis of C.oleifera.（2）Effects of AM fungus and nitrogen application on nitrogen uptake of C.oleiferaWith the increase of N level,the total N content of C.oleifera root and stem leaves continued to increase,the nitrogen utilization efficiency（NUE）of leaves and stems first increased and then decreased,and the NUE of C.oleifera root decreased,showing high total nitrogen content and low NUE under high N（N3）level.Inoculation of AM fungi increased leaf total nitrogen content（20.09%,13.36%）and stem total nitrogen content（36.62%and60.73%）at N0 and N1 levels;increased root total nitrogen content（45.79%）at N0 level;inoculation of AM fungi increased root（60.67%）and leaf（63.96%）NUE at N3 level.The result showed:AM fumgi could improve the total nitrogen content of C.oleifera at N0 and N1 levels,while inoculation of AM fungus did not have significant effect on the total nitrogen content of C.oleifera at N3 level,but could improve the NUE.（3）Effects of AM fungi and nitrogen application on nitrogen assimilating enzyme activity and relative gene expression.Inoculation of AM fungi and nitrogen application both improved nitrate reductase（NR）,glutamine synthetase（GS）and glutamate synthetase（GOGAT）enzyme activities.Inoculation of AM fungi affected root nitrogen metabolizing enzyme activities,and inoculation of AM fungi significantly increased NR（14.96%）,GS（34.91%）and GOGAT（23.83%）enzyme activities in roots of C.oleifera at N3 level.At the N0 and N1 levels,inoculation of AM fungi up-regulated the relative expression of leaf nitrogen assimilation enzyme genes and down-regulated the relative expression of root nitrogen assimilation enzyme genes.（4）Effects of AM fungus and nitrogen application on the relative expression of nitrogen uptake related transporter protein genes.Compared with no nitrogen application,nitrogen application up-regulated the relative expression of ammonium transporter protein genes and nitrate transporter protein genes in C.oleifera leaves and roots.Inoculation of AM fungi increased the relative expression of leaf and root nitrate transporter protein genes,and inoculation of AM fungi decreased the relative expression of root Co AMT2.1a,Co AMT1.1a and Co AMT1.1b genes,and increased the expression of leaf Co AMT1.2a,Co AMT3.1a and Co AMT1.1b genes.（5）Effect of AM fungi on the loss of nitrogen leaching from C.oleifera soilNitrogen application increased the content of ammonium nitrogen（NH₄⁺）and nitrate nitrogen（NO₃^-）in the leachate,and increased the soil hyphal density,balloon mold,organic carbon（SOC）,soluble organic carbon（DOC）,total nitrogen（TN）,soluble total nitrogen（DTN）,NH₄⁺,and NO₃^-content in the soil,Reduced p H content.Inoculation with AM fungi decreased soil p H,DOC,DTN,and NH₄⁺content,and increased glomalin-reactive soil protein,SOC,TN,and NO₃^-content.The results showed that under the high nitrogen nitrogen level,inoculation of AM fungi can slow down the nitrogen leaching loss of C.oleifera soil,especially the NH₄⁺leaching,under the higher N level.The redundancy analysis results indicate that DTN and DOC are the three most important soil factors affecting soil nitrogen leaching loss of C.oleifera Factors.