| We choose plantations and secondary forests of Pinus tabulaeformis with similar stand conditions in Huanglong Mountain forestry region of Shaanxi province and Ziwuling Mountain forestry region of Gansu province.Soil samples were collected from the rhizosphere of trees and seedlings,to analyze the differences of soil physicochemical properties and enzyme activities in two forest origins,and the structure and diversity of phosphate solubilizing bacterial community were studied,to reveal the effects of forest origin and soil physicochemical properties on phosphate solubilizing bacterial communities in rhizosphere of Pinus tabulaeformis.At the same time,the functions of soil microorganisms on the growth of Pinus tabulaeformis seedlings were studied,in order to reveal the effect of forest origin on the regeneration of Pinus tabulaeformis on the theory of soil microorganism,by laying pot experiments with the soil collected in the rhizosphere of Pinus tabulaeformis seedlings and using sterilized soil as control.The main findings and conclusions are as follows:(1)Soil physicochemical properties in the rhizosphere of Pinus tabulaeformis of two forest origins were significantly different in the study area,which had a significant effect on soil enzyme activity,among which soil water content,p H,total nitrogen and organic carbon content contributed the most to alkaline phosphatase and urease activity.(2)A total of 7 kinds of inorganic phosphorus bacteria and 8 organophosphorus bacteria were isolated in this study.The species of phosphorus bacteria in the rhizosphere of plantation and secondary forest are similar,and they share the same inorganic phosphorus bacteria like Pseudomonas sp.strain YL-MPn-6,Paraburkholderia Fungorum strain ATCC BAA-463,Phyllobacterium brassicacearum strain MR4,Ochrobactrum sp.F12(2011),Acinetobacter Bereziniae strain XH901 and bacterium A31514 and they share the same organophosphorus bacteria like Burkholderia cenocepacia strain PC184,Paenibacillus sp.strain RS13,Pseudomonas mandelii strain IHBB 9472,Pseudomonas sp.RB5,Pseudomonas sp.strain BGI and uncultured Pseudomonas sp.clone 12.(3)The species of phosphate solubilizing bacteria(PSB)in the rhizosphere of seedlings in plantation are also close to these in secondary forest,and share the same inorganic phosphorus bacteria like Oobactrum sp.F12,Acinetobacter pittii strain 2010C01-170,Acinetobacter Bereziniae strain Xh901,Pseudomonas sp.strain Yl-MPn-6,paraburkholderia Fungorum strain ATCC BAA-463,etc.and they share the same Organophosphorus bacteria like Burkholderia cenocepacia strain PC184,Pseudomonas mandelii strain IHBB 9472,Pseudomonas sp.strain BGI-2,Rhizobium sp.CC-RB302,Paenibacillus sp.strain RS13,etc.Microbacterium trichothecenolyticum strain E-5 and Uncultured bacterium clone A5-025 are also found in the rhizosphere of Pinus tabulaeformis seedlings in the plantation.(4)The diversity of shrub and herb under Pinus tabulaeformis forest is greatly influenced by the origin of forest,and they have important influences on the microorganisms in the soil together with the physical and chemical properties of the soil.Among them,shrub cover,herb cover,soil p H value,organic carbon content and carbon-nitrogen ratio are the main factors affecting the diversity of phosphorus bacteria in the rhizosphere of Pinus tabulaeformis.(5)The pot experiment shows that the rhizosphere soil of plantation and secondary forest have little effects on the composition of phosphorus bacteria in the rhizosphere of pot seedlings,and the inorganic phosphorus bacteria have Pseudomonas sp.strain Yl-MPn-6,Paraburkholderia Fungorum strain ATCC BAA-463;organophosphorus bacteria have Pseudomonas sp.strain BGI-2.Ochrobactrum sp.F12(2011),Pseudomonas mandelii strain IHBB 9472 were also isolated from the pot soil of natural forests.In terms of phosphorus bacterial diversity,the Shannon Index and Simpson Index of phosphate solubilizing bacteria in the pot soil of natural forest are higher than that of plantation soil,while Pielou Index J and Richness Index s shows the opposite trend.(6)The sterilization treatment of pot soil confirms that soil microorganisms could promote the growth and development of Pinus tabulaeformis seedlings and the accumulation of phosphorus in vivo,significantly improve the plant base diameter,leaves length,root surface area,root biomass and stem length and phosphorus content;without functional microorganisms such as mycorrhizal fungi and phosphorus bacteria,Pinus tabulaeformis seedlings can grow normally,However,the increasement of growth is lower than that of control treatment,which indicates that soil microorganism has a influence on natural regeneration of Pinus tabulaeformis.The above results show that the origin of forest not only has a significant effect on soil physicochemical properties and enzyme activity,but also affects the diversity of undergrowth shrubs and herbs,which has a profound influence on the population and community structure of phosphorus bacteria in rhizosphere soil of Pinus tabulaeformis.Soil microorganisms play a positive role in promoting natural regeneration of Pinus tabulaeformis. |
