Effect Of Different Continuous Cropping And Rotation Of Poplar Plantation On Soil Nitrogen Bacteria Community Charatteristics And Nitrogen Metabolism

Nitrogen is the most important element for poplar plantation productivity. Studying the nitrogen cycle bacteria community evolution and structure features of nitrogen metabolism from continuous cropping and rotation of poplar plantation are in favour of revealing the mechanism poplar plantation continuous cropping obstacles from the angle of nutrient cycling. This article used the Metagenome sequencing technology to study the community of soil nitrogen cycling bacteria and the evolvement rule of nitrogen metabolism along with the continuous cropping generation and different rotation patterns in Ⅰ generation poplar plantation, continuous cropping Ⅱ generation poplar plantation,rotated peanut field and the abandoned land after poplar clear cutting. The results showed that:(1) Found bacteria associated with the nitrogen cycle having genus 4 class 11, which were : Azotobacter, Beijerinckia, Bradyrhizobium, Rhizobium, Frankia; Nitrobacteria, nitrobacter, nitrosospira; Denitrifying bacteria, pseudomonas, ralstonia, burkholderia, bacillus, streptomyces, Ammonifying bacteria, Bacillus, Pseudomonas.(2) Compared with Ⅰ generation poplar plantation, the total number of nitrogen cycling bacteria in the soil increased by 4.73%, the type of nitrogen bacteria in the soil were unchanged in Ⅱ generation poplar plantation. The abundance of nitrogen fixing bacteria increased by 53.44%, nitrification bacteria were unchanged, the denitrification bacteria increased by 0.14%, ammonifying bacteria increased by 1.33% in Ⅱ generation poplar plantation. After the rotation of peanut, there was no increase or decrease in the type of nitrogen in the soil. The abundance of nitrogen fixing bacteria reduced by 71.14%, nitrifying bacteria, denitrifying bacteria and ammonifying bacteria abundance increased by 120%, 15.63% and 20.76%. Compared with Ⅱ generation poplars, after Ⅱ generation poplars clear cutting, species and abundance of nitrogen cycling bacteria in the abandoned land changed. Among them the abandoned land were lack of nitrification bacteria. The abundance of nitrogen fixing bacteria reduced by 79.10%, denitrifying bacteria and ammonifying bacteria increased 17.39%, 24.56% respectively.(3) Compared with Ⅰ generation poplar plantation, the metabolic activity of soil azotobacteria enhanced, Nitrobacter weakened, while Nitrosospira enhanced, ammonifying bacteria weakened in Ⅱ generation poplar plantation. After Ⅱ generation poplars clear cutting, only the metabolic activity of the nitrification bacteria increased, and the other four kinds of nitrogen metabolism function bacteria decreased in rotated peanut field. After Ⅱ generation poplars clear cutting, the metabolic activity of nitrogen cycling bacteria in the abandoned land were lower than that of in the Ⅱ generation of poplar plantation.(4) Compared with Ⅰ generation poplar plantation, soil nitrogen fixation and denitrification intensity increased by 14.29% and 2.55%, while ammonification and nitrification intensity reduced 12.90% and 5.24% in Ⅱ generation poplar plantation. Compared with Ⅱ generation poplars, after the rotation of peanuts the intensity of soil nitrification and ammonification increase by 20.20%, 3.70%, denitrification and nitrogen fixation decreased by 8.81%, 70.83% respectively. The four kinds of nitrogen transformation intensity in the wasteland were lower than that of the peanut field.In short, after the first continuous cropping of poplar plantation, the total number of bacteria in the soil was increased, but the metabolic activity was decreased. The intensities of nitrogen fixation and nitrification were increase in forest soil. After the rotation of peanut, the number of bacteria increased significantly, but only the metabolic activity of the nitrification bacteria increased significantly. The intensity of soil nitrification increased by 3.95%. So rotation could improve the growth and metabolic activity of nitrification bacteria, which were caused by continuous cropping of poplar plantation and then improve the intensity of the nitrification in forest.