Soil Nitrogen Mineralization And Microbial Characteristics Of Pinus Sylvestris Var. Mongolica Forest With Different Ages And Densities

The availability of soil nitrogen?N?is a key limiting factor for the productivity and stability of sandy forest ecosystems.In order to systematically study the soil nitrogen mineralization and microbial biomass characteristics and their changes in Zhanggutai Pinus sylvestris var.mongolica plantation,the Pinus sylvestris var.mongolica plantations with different forest ages and different densities were studied,to determine the changes of soil NH₄⁺-N,NO₃^--N,mineral N,ammoniation rate,nitrification rate,mineralization rate,soil respiration intensity,microbial biomass C,N and the variation of 0¹00cm soil layer.By analyzing the coefficient of variation in different forest ages,different densities and different soil layers,to revealed the degree of uniformity of spatial distribution of each index.The test results provide the effective supply of soil N in different forest ages,different densities and different soil layers in sandy land,and provide a theoretical basis for the sustainable management and evaluation of Pinus sylvestris var.mongolica plantation.Research indicates:?1?With the increase of forest age,NH₄⁺-N content increased,reaching a maximum at60a.The content of NO₃^--N and mineral N growth rate in 20a⁵0a increased significantly,reaching the maximum at 50a.It can be considered that the soil N has the best effectiveness when the forest age is 50a.The ammoniation rate,nitrification rate and mineralization rate all showed an increasing trend.The ammoniation rate and mineralization rate reached the maximum at 50a,and the nitrification rate reached the maximum at 60a,but the difference was not significant with 50a.It is considered that when the forest age is 50a,the soil nitrogen supply capacity is the best.The soil microbial biomass of Pinus sylvestris var.mongolica plantations varied greatly with different forest ages,and increased with the increase of forest age.The microbial biomass C and N peaked at 40a and 30a,respectively,indicating that Pinus sylvestris var.During the forest period,the microbial biomass is the best.?2?The soil mineralization index and microbial index of Pinus sylvestris var.mongolica forest in the growth stage of young forest,middle-aged forest,mature forest and over-ripe forest increased with the increase of density,and the afforestation density was too small.The effectiveness of soil nitrogen cannot be fully utilized.Therefore,a suitable afforestation density can increase the amount of microorganisms and microbial activity.?3?With the increase of soil depth,the mineral N content and mineralization rate are gradually reduced.The mineral nitrogen in 0⁴0cm soil layer is higher than 40¹00cm,showing surface aggregation.The microbial biomass of the 0²0cm soil layer in the vertical space is the highest.?4?There was a significant positive correlation between the index and plant height,DBH,crown width and soil organic carbon,total nitrogen and alkali nitrogen in Pinus sylvestris var.Through redundancy analysis?RDA?,the main environmental factors affecting soil mineralization index of different forest ages are SOC;the main environmental factors affecting soil mineralization indexes of different soil layers are HN,TN and SOC.The main environmental factors affecting the microbial properties are soil SOC,TP and HN.?5?Different forest ages of Pinus sylvestris var.mongolica plantation can effectively improve the soil nitrogen availability in sandy land,but the improvement process is long.According to the comprehensive analysis,the mineralization of soil nitrogen is best when the forest age is 50a and the density is 670 plants/hm².The optimal afforestation density of Pinus sylvestris var.mongolica is different at each growth stage.The density of plantation should be adjusted in time to make soil nitrogen.The effectiveness is optimal.