Change And Mechanism Of Nutrient And Microbial Characteristics Of Robinia Pseudoacacia Forest Along Environmentalgradient In Loess Plateau

Changes in nutrient and microbial characteristics of terrestrial forest ecosystems are affected by factors such as climate,soil and vegetation,but studies have focused on the effects of soil factors on ecosystems,and on climate and soil changes along environmental gradients.How factor coupling affects the microbial characteristics of plants,soils and soils in forest ecosystems is not well understood.In this paper,the artificial Robinia pseudoacacia forest widely distributed in the Loess Plateau was taken as the research object.The four regions of Shenmu,Jude,Ansai and Suihua were selected from the north to the south along the environmental gradient.The nutrient characteristics of various organs of the artificial Robinia pseudoacacia ecosystem were studied.C,nitrogen N,phosphorus P content and its stoichiometric ratio),soil physical properties?weight,texture,water-stable agglomerates,etc.?,chemical properties?pH,C,N,P,available phosphorus AP,etc.?and dispersion The changes of microbial characteristics?microbial biomass,soil enzymes,community characteristics?along the soil gradient and the driving mechanism of soil and rhizosphere soil are as follows:1.From north to south,the physical and chemical properties of forest soil are as follows:?1?Soil bulk density decreases first and then increases;cosmid and powder content increase,sand content decreases;particle size<0.053mm,>The weight percentage of 0.25mm agglomerates increased first and then decreased,and the weight of 0.053-0.25mm agglomerates decreased first and then increased;the water content of loose soils showed an upward trend;while the water content of rhizosphere soil increased first and then decreased.?2?In the loose soil,the pH changed from 8.15 to 8.46,showing a decreasing trend;AP,N and P contents increased;NH₄⁺-N,NO₃^--N,SOC content and C/N,C/P First increase and then decrease and then increase,reaching the maximum in the Suihua area;N/P decreases first and then increases,and reaches the minimum in the Jude and Ansai areas;?3?Changes in the physical and chemical properties of rhizosphere soil and loose soil The trend is similar.The content of AP and N increased,and the pH decreased.NH₄⁺-N,NO₃^--N,SOC and C/P increased first and then decreased.N/P decreased from 1.59 to 3.33.Increase after small;P,C/N increase first and then decrease.2.From north to south,the biomass of the hedgehog and the stoichiometry of each organ showed:?1?the biomass of the hedgehog decreased first and then increased,and the biomass of the Ansai area was the highest(166.49 kg.m^-2);There was no significant change in the content of organic carbon?OC?in the stems,<1mm roots,and>2mm roots.The OC of1-2mm decreased first and then increased.The total N and P of leaves and branches showed a decrease first and then increased.The change was reduced;the N and P contents in the roots of all diameter grades increased first and then decreased.?2?The C/N and C/P stoichiometric ratios of Robinia pseudoacacia leaves in Suihua area were significantly higher than those in other areas;N/P in the range of 18.27²3.66 increased first and then decreased from north to south.The stoichiometric ratios of C.sylvestris L.,C/P and N/P decreased first and then increased.The roots of the roots of C.sylvestris C/N,C/P and N/P showed a decrease first and then increased.Trends;?3?N and P of the organs of the hedgehog were negatively correlated with the annual mean temperature?MAT?.The branches and roots of the hedgehog were negatively correlated with the average root rainfall N,P and annual mean rainfall?MAP?.There was no significant correlation between OC content in various organs and climatic factors.From north to south,the changes of soil microbial biomass and soil enzyme characteristics in forest land are as follows:?1?Microbial biomass carbon?MBC?,microbial biomass nitrogen?MBN?,microbial biomass phosphorus?MBP?,MBC/MBP in loose soil Both showed an increasing trend;MBC/MBN decreased first and then increased,and MBN/MBP increased first and then decreased.The MBC,MBN,MBP,MBC/MBP and MBN/MBP in the rhizosphere soil increased first and then decreased;MBC/MBN increased first and then decreased and then increased;?2?The activity of leucine?LAP?in the loose soil continued.When increased,the activities of glucosidase?BG?,acetylglucosidase?NAG?and alkaline phosphatase?AP?increased first and then decreased.Among them,BG/?LAP+NAG?and BG/AP ranged from 3.43 to 6.46 and 1.5 to 2.96,first decreasing and then increasing;?LAP+NAG?/AP was in the range of 0.41⁰.7,which continued to decrease.The AP in the rhizosphere soil continued to increase,and the activities of BG,NAG and LAP increased first and then decreased.BG/?LAP+NAG?,BG/AP,and?LAP+NAG?/AP are in the range of2.90³.83,3.36⁴.92,1.18¹.45,respectively,and then increase and then decrease and then increase the trend;?3?Redundancy analysis?RDA?showed that MAP and N/P accounted for36.6%and 14.8%of the activity of the loose soil enzyme and the amount of microorganisms,respectively.A-P and TN respectively accounted for 30.5%and 19.1%of the stoichiometric ratio of loose soil enzyme to microbial biomass.MAP and RP1 accounted for 27.4%and10.1%of soil enzyme activity and microbial biomass,respectively.TN and RC1 respectively accounted for 17.4%and 17.1%of the stoichiometric ratio of soil enzyme to microbial biomass.4.The bacteria Chao1 index in the loose soil of forest land is in the range of2878.68³306.70.It decreases from north to south and then decreases and then decreases.The fungus Chao1 index is in the range of 600.50⁷26.65,and the trend is opposite to that of bacteria.The Shannon index of bacteria is in the range of 6.39⁶.67,first decreasing and then increasing;the Shannon index of fungi is in the range of 2.84⁴.22,first decreasing and then increasing and then decreasing.The bacteria gates with relatively high abundance of microbial communities in the loose soil are Proteus,Actinobacteria,Acidophilus,and Clostridium.The fungal gates with relatively high abundance are Ascomycetes and Basidiomycetes.From north to south,the community-specific differences in the level of the genus are less variable.The interpretation rates of environmental factors,soil nutrients and biological factors on loose soil bacteria were 32.01%,28.64%and 29.96%,respectively.The interpretation rates of environmental factors,soil nutrients and biological factors on loose soil fungi were 18.56%and 19.29 respectively.%,17.44%.5.The Chao1 index of rhizosphere soil bacteria in the dominant species of woodland is in the range of 1086.63¹146.68.From north to south,first decrease and then increase and then decrease;fungus Chao1 in the range of 228.43²87.96,first decrease and then increase and then decrease.The Shannon index of bacteria decreased from 5.89 to 6.04,then decreased first and then decreased.The fungal Shannon index ranged from 2.95 to 3.30,first decreasing and then increasing.From north to south,the community with specific differences in the level of bacteria in the rhizosphere showed a decreasing trend;the group with specific differences in the level of the rhizosphere of the fungi first decreased and then increased.The interpretation rate of environmental factors,microbial factors and plant factors on rhizosphere bacteria was 45.73%,32.29%and 41.15%,respectively.The interpretation rate of environmental factors,microbial factors and plant factors on rhizosphere fungi was 47.86%,31.67%and 40.22%,respectively.In short,the growth of Robinia pseudoacacia in the Loess Plateau is generally limited by the content of N and P in soil.The N/P of plant leaves in the study area was greater than 16,indicating that the P element restriction was more serious,and from north to south,the plant P element restriction first weakened and then enhanced.Soil enzyme ln?BG?in loose soil:ln?NAG+LAP?:ln?AP?is 1:0.65:1.25,rhizosphere soil enzyme ln?BG?:ln?NAG+LAP?:ln?AP?is 1:1.1:0.97.It indicated that the microbial nutrients in the community were mainly restricted by P element,and the microbial nutrients in the rhizosphere soil were weakly restricted.The microbial community in the loose soil was in an unsteady state,and the microbial community in the rhizosphere soil was in a relatively stable state.The dominant species of the bacterial and fungal communities in the community and rhizosphere soils in the four regions were basically the same,but the relative abundance was different.In addition,each region has a unique microbial population in the region,such as the sulphate-specific microbial chlorosulfur bacteria?Chlorobi?.Climatic factors significantly affect bacterial and fungal community characteristics.The results of this paper provide basic data for soil nutrient cycling control in forest ecosystems,and provide reference for regional plantation management.