Study On The Microbial Community Structure About Soil Nitrogen Cycling In Pinus Tabulaeformis Plantation On The Loess Plateau

Soil nitrogen cycling refers to the general term for the process of mutual transformation of N₂,inorganic nitrogen compounds,and organic nitrogen compounds in the natural world.It mainly includes ammoniation,nitrification,and denitrification.Soil microorganisms are the main drivers of the nitrogen cycle.It regulates nitrogen fixation,nitrification,and denitrification processes thro?gh the synthesis of nitrogen reductase,ammonia monooxygenase,and nitrate reductase involved in nitrogen transformation.The development stage of Pinus tabulaeformis plantation will change the vegetation composition in the forest land,and the structure and function of soil microbial community will change with it,which will affect the nutrient cycling and transformation of forest soil.Therefore,qualitative and quantitative studies on the evolution of functional community structure of soil nitrogen cycle at different growth stages of P.tabulaeformis plantations will be helpful to understand the nitrogen transformation process and its influencing mechanism of P.tabulaeformis plantation ecosystem.In this study,P.tabulaeformis plantations located in the gully region of the Loess Plateau were used as research objects to study the functional gene abundance and community structure changes of the soils participating in the soil nitrogen cycle.At the same time,the relationship between soil environmental factors and soil microbial community structure were studied.The main results obtained are as follows:?1?After the conversion from abandoned land to P.tabulaeformis plantation,the soil organic carbon and total nitrogen contents of the 10-year-old stands were all significantly reduced.which was reduced by 15.42%and 18.81%compared with the abandoned land.With the growth and development of P.tabulaeformis plantation,the content of soil organic carbon,total nitrogen,ammonium nitrogen,and available potassium gradually increased,and the maximum value appeared in the forest land of 45 years old.The soil pH and available phosphorus content did not change significantly during the development of forest stands.The activity of?-glucosidase,cellulase,urease,protease,and alkaline phosphatase increased with the increase of forest age,and reached its maximum in 45-year-old stands,which was74.42%-376.92%compared with the abandoned land.With the increase of plantation age,the microbial biomass carbon,microbial biomass nitrogen and nitrification potential activity increased significantly,the potential denitrification activity had no obvious change.?2?There were significant differences in gene abundances of soil nitrogen cycle function in P.tabulaeformis artificial forest lands of different ages.When transformed from abandoned land to P.tabulaeformis plantations,the gene abundance of ammonia-oxidizing bacteria?AOB?,ammonia-oxidizing archaea?AOA?and denitrification genes?narG,nirK,nirS,and nosZ?showed different degrees of increase.However,the development of forest stands had no significant effect on the abundance of AOB.The correlation analysis between nitrogen cycle functional gene abundance and soil nutrient showed that there was a significant positive correlation between AOA gene abundance and soil organic carbon,total nitrogen,ammonium nitrogen,and available potassium.The denitrification gene abundance was significantly positively correlated with organic carbon,total nitrogen,ammonium nitrogen,and available potassium,and was significantly negatively correlated with pH and nitrate nitrogen.?3?With the increase of forest age,the richness of AOA community decreased,the diversity of AOA community increased.the richness of denitrifying microbial communities with narG and nirS genes had no significant difference,the richness of denitrifying microbial communities with nirK gene gradually increased first and then decreased,and the diversity had no significant difference.The richness and diversity of denitrifying microbial communities with nosZ gene gradually decreased.The main dominant phylum of AOA community is Crenarchaeota.In the denitrifying bacteria containing narG gene,Pseudomonas was the dominant genus,and its relative abundance increased with the growth of forest age.The denitrifying bacteria containing nirK gene mainly belonged to Ensifer,Sinorhizobium,Mesorhizobium and Achromobacter.The relative abundance of Sinorhizobium and Mesorhizobium increased with the growth of forest age.The denitrifying bacteria containing nirS gene mainly belonged to Pseudomonas,Rhodendron and Azospirillum.During the development of forest stands,the relative abundance of Pseudomonas was gradually increased,the relative abundance of Rhodendron and Azospirillum were gradually reduced.The denitrifying bacteria containing nosZ gene mainly belonged to Pseudomonas and Rhodobacter.The relative abundance of Rhodobacter and Pseudomonas in the10-year-old and 20-year-old stands were significantly higher than those of other stands.Besides,the microbial community structure of AOA was affected by NO₃^--N and pH.TN,NO₃^--N,pH and SOC significantly affected the microbial community structure of the denitrifying bacteria containing narG,nirK,nirS and nosZ.