Effects Of Arbuscular Mycorrhizal Fungi On The Nitrogen Nutrition Of Poplar

The influence of arbuscular mycorrhizal(AM)fungi on plant nitrogen nutrition is unclear.In this thesis,the relationship between the growth of Populus × canadensis 'Neva'and soil carbon,nitrogen content,and AM fungi distribution were studied.The effects of AM fungi(Rhizophagus irregularis)inoculation on the growth of P.× canadensis 'Neva'under different N application levels were studied.Three potential mechanisms of AM fungi on N nutrition of P.× canadensis 'Neva' were examined:(1)the N/C exchange between AM fungi and poplar,(2)the impact of AM fungi on poplar N absorption,and(3)the effects of AM fungi on the N interception in poplar-soil microsystems.The main results are as follows:1.Relationship between poplar growth,soil C,N content,and AM fungi distribution.In the pot experiment,the ground diameter of the poplar cutting seedlings was used as the growth index,the results showed that,as the ground diameter increased,the soil inorganic carbon(SIC)and nitrate nitrogen(NO3-)content decreased.NH4+ also decreased but the decrease was not significant.The content of soil organic carbon(SOC),total carbon(TC)and soil organic nitrogen(SON),total nitrogen(TN)increased.The spore density did not change with increased ground diameter but the infection rate increased.SON and TN contents were significantly positively correlated with arbuscular infection rate,while NO3-and NH4+contents were significantly negatively correlated with arbuscular infection rate.Spore density was not correlated with C or N components.The results indicated that the better the growth of P.× canadensis 'Neva',the lower the NO3-and SIC content,and the higher the root AM fungi infection rate.However,the distribution of AM fungi in the soil did not change significantly and the content of NO3-in the soil was strongly related to the distribution of AM fungi in poplar roots.2.Effects of AM fungi on the growth and wood characteristics of P.× canadensis'Neva'.The significance of the inoculation treatment varied with different N application levels.Inoculations of N were made at concentrations of 0,1.0,5.0,7.5,10.0,15.0,and 20.0 mM NH4NO3.Plant height,stem biomass,cellulose content,and fiber length of poplar reached a maximum at the 7.5 mM level.AM fungi increased plant height and stem biomass,which reached significance at levels?7.5 mM,and raised the crown/root ratio at all N levels.At the 15 mM and 20 mM N levels,AM fungi significantly increased stem cellulose content,and significantly reduced the stem fiber wall-cavity ratio at 20 mM N level.At all N levels,AM fungi improved stem fiber length,aspect ratio,but did not significantly affect stem lignin content and the stem lignin monomer S/G ratio.AM fungi promoted the growth of poplar,and the specific quality of poplar was improved under a specific N level.The 7.5 mM N concentration was optimal for poplar growth.3.Effects of AM fungi on the photosynthetic capacity of poplar and N/C exchange between AM fungi and plants.AM fungi can increase the photosynthetic carbon sequestration capacity of poplar,increase C accumulation,and can promote the C/N exchange between poplar and AM fungi Treatment of AM fungi at a low N level(1 mM)did not significantly affect leaf structure.At the optimum(7.5 mM)and high(20 mM)N level AM fungi significantly increased the thickness of the leaf sponge tissue.At the same time,the leaf area increased by 20.8%and 33.3%,the stomatal length increased by 5.9%and 6.0%,the content of chlorophyll-a increased by 69.9%and 58.7%,and the content of chlorophyll-b increased by 74.2%and 38.6%,respectively.AM fungi can increase the photosynthetic rate of poplar at a light intensity?400 ?mol m-2 s-1.Analysis of C and N content in poplar roots,stems,and leaves showed that under optimum and high N levels,AM fungi significantly increased the total accumulation of plant C.At the same time,the N concentration of poplar roots and the plant total N increased.Mycorrhizal infection rate and arbuscular infection rate both increased with increased N levels.Under low N levels,the arbuscular development was poor,while under optimum and high N levels,the arbuscular structure had better development.Under the optimum and high N conditions,AM fungi promoted plant photosynthesis and carbon sequestration.The arbuscular structure developed well,the N/C exchange between AM fungi and poplar was strengthened,and the N nutrition of poplar was improved.A light intensity?400 ?mol m-2 s-1 facilitated this process.4.Effects of AM fungi on the nitrogen nutrition of poplar.Although AM fungi inoculation reduced the poplar root system,it increased the overall metabolic level and promoted poplar N absorption.Under the low,optimum,and high N treatment levels,AM fungi decreased poplar root length and root surface area but increased the root activity,transpiration rate,nitrate reductase activity,and glutamine synthetase activity in leaves,and the water content of leaves,stems,and roots.This indicated improved overall metabolic capacity of poplar.At low,optimum,and high N levels,and inoculation with AM fungi,the root auxin content was respectively 2.3,1.9,and 2.9 times that of the non-inoculation group.At low and optimum N levels,the root gibberellin content increased by 85.1%and 94.2%,respectively.After inoculation,cytokinin and abscisic acid varied at different N levels,but neither had significant changes.The root cell wall cellulose content was reduced at all N levels(only significant at low N level),while the lignin monomers H,S,G,and S/G ratio all increased.At the low and optimal N levels,AM fungal inoculation increased the lignin monomer H by 34.3%and 64.0%,respectively.The increase of lignin monomer S and the S/G ratio were significant at a low N level,and increased by 37.0%and 18.8%,respectively.Correlation analysis showed that,at a low N level,lignin monomer S/G was significantly positively correlated with root gibberellin and auxin content.At a high N level,auxin content and monomer S content were significantly positively correlated.These results indicated that AM fungus damaged the components of the plant cell wall(reduced cellulose).To start the defense reaction(synthetic lignin),the levels of gibberellin and auxin were increased,the overall metabolism of poplar was improved,and N absorption was promoted.5.Effects of AM fungi on N leaching from poplar-soil microsystems.Under different N application levels,AM fungi displayed large differences in N leaching from poplar-soil microsystems.At a low N level,AM fungi had no effect on soil N leaching.At optimal and high N levels,AM fungi reduced NO3-and NH4+ concentrations in the leachate.This only reached significant levels under high N conditions.At a high N level,inoculation with AM fungi reduced the NO3-and NH4+concentrations in the leachate by 20.0%and 67.5%,respectively.With an increase in the N level,the arbuscular infection rate and total infection rate increased and the morphology of spores and vesicles were altered.After inoculation of AM fungi at the optimal and high concentration,the root N concentration increased(11.7%and 50.7%,respectively).At the same time soil cation exchange capacity(CEC),SOC content and the proportion of large aggregates increased.Also,soil TN content increased by 7.2%and 4.7%,respectively.Redundancy analysis showed that,at the high N level,among all variables,SOC had the greatest relative explanation rate for total amount of NH4+ and NO3-in leachate;while the results of correlation analysis showed that at the high N level,the total amount of NH4+ and NO3-in leachate had the greatest correlation with SOC content,which displayed a significantly negative correlation.AM fungi reduced soil N leaching,and the reduction of NH4+ leaching was particularly significant.AM fungi can enhance poplar interception of N in the soil,increase exposure to soil N,and improve N nutrition.