Research On Rhizosphere Bacteria And Ecological Function Characteristics Of Robinia Pseudoacacia L.Plantation

Robinia pseudoacacia L.is a main species planted on the Loess Plateau and plays a vital role in the stability and sustainability of the region’s ecosystem.Rhizosphere microbes are drivers and responders of the ecosystem.Although studies have shown that there is an interaction between Robinia-soil-microbes,the effect of soil microbial communities on the ecological functions of Robinia plantations and its mechanism are unclear.In this study,the differential microbial in the rhizosphere and keystone species in the co-occurrence networks at different developmental stages were identified using high-throughput sequencing technology in Robinia plantations of different ages（10,20,and 32 years old）in the gullies of the Loess Plateau.The dominant bacteria with plant growth promotion properties were also selected from rhizosphere soil of Robinia plantations by the dilution plate method.Based on differential rhizosphere bacteria,keystone species in the co-occurrence network and dominant plant growth promotion bacteria,synthetic communities were constructed and the effects of synthetic communities on the growth of Robinia were investigated,and the main research results obtained were as follows:（1）During the growth and development of Robinia plantations,the content of available phosphorus（AP）in rhizosphere soil gradually decreased and the degree of plant growth restricted by soil phosphorus gradually increased.The rhizosphere bacterial community was dominated by genera include Subgroup＿6,Pseudomonas,KD4-96 and Streptomyces.Genera Arthrobacter and Kribbella were relatively abundance increased significantly with the increasing stand age,while genera Ramlibacter and MND1 showed the opposite trend.The network structure of rhizosphere bacteria differed significantly among different stand ages.The 32-year-old Robinia plantation had the simplest network structure and the highest degree of modularity,but the competition among species was the strongest.The keystone species changed from one genus（Ramlibacter）in the 10 y to five genera in the 32-y,respectively Bradyrhizobium,Pseudolabrys,Subgroup＿17,Ramlibacter and Burkholderia-Caballeronia-Paraburkholderia,which mainly play a role in soil phosphorus cycling.Soil p H,soil organic carbon（SOC）,total nitrogen（TN）,nitrate nitrogen（NO₃^--N）,ammonium nitrogen（NH₄⁺-N）,soi N:P and C:P were important drivers of changes in the rhizosphere bacterial community of Robinia plantations.（2）A total of 256 rhizosphere bacterial strains were isolated from the rhizosphere of Robinia plantations,of which 60 strains had the ability to solubilize phosphorus,with the phosphorus solubilization amount ranging from 2.24μg/m L-72.33μg/m L;135 strains had the ability to fix nitrogen;40 strains were able to produce IAA,with the IAA production amount ranging from 2.54μg/m L-8.14μg/m L;10 strains had drought resistance and grew well at 25%PEG 6000 concentration.Combining the probiotic properties of the strains,seventeen dominant plant-growth-promotion-bacterias were selected,belonging to Pseudomonas sp.,Serratia sp.,Bacillus sp.,Sphingobacterium sp.,Phyllobacterium sp.and Acidovorax sp.respectively.In addition,the sequences of keystone species in the co-occurrence network and dominant plant-growth-promotion rhizosphere strains were compared,and Phyllobacterium myrsinacearum and Acidovorax temperans（dominant plant growth promotion rhizosphere bacteria）were identified as keystone species in the co-occurrence network of rhizosphere bacterial communities.（3）Four synthetic communities were constructed by combining the keystone species in the co-occurrence network and dominant plant growth promotion rhizosphere bacteria according to the principle of functional superposition and synergism,and the function of synthetic communities was tested by pot experiment with soil with phosphorus deficiency（soil of the 32-year-old Robinia plantation）.It was found that after the inoculation of synthetic communities,the activity of soil alkaline phosphatase and urease increased by17.69%-59.23%and 2.65-3.90 times,respectively compared with the control group;the soil nutrient contents increased by 1.61-2.70 times,1.07-1.54 times and 1.23-1.46 times respectively compared with the control group;root vitality increased by 1.76-5.79 times respectively compared with the control group;and the leaf N:P decreased by 49.27%-71.09%compared to the control.The inoculation of synthetic communities effectively alleviated the phosphorus limitation of Robinia plants.