Effects Of Stand Density On Vertical Change Of Soil Properties Of Pinus Tabulaeformis Natural Secondary Near-mature Forest

Strengthening the management of natural secondary forest,adjusting stand structure reasonably and achieving accurate forest quality improvement are the real problems facing sustainable forest management.To study the effect of stand density on soil property indexes of natural secondary near-mature forest are helpful to understand the response mode of forest soil to stand density regulation and to determine the role of near-mature forest density regulation.Pinus tabulaeformis is a unique tree species in China,one of the most important tree species in the Loess Plateau,and one of the representative coniferous forests in North China.the study was conducted in a natural secondary near-mature forest of Pinus tabulaeformis(age class? to ?)in Guandishan Forest Region xiaowenshan farm.Through sample area investigation,soil sampling and attribute index determination,soil physicochemical properties,microbial biomass carbon and nitrogen and their vertical distribution characteristics,of 0~30cm soil with different natural secondary forest stands densities(700~1400trees?hm-2)were analyzed,and it is important to optimize the existing forest management model in the study area,adopt appropriate adjustment measures to improve forest soil,and accurately improve the quality of natural secondary near-mature forest of Pinus tabulaeformis.The results showed that:(1)The change in stand density significantly influenced the water content,bulk density,p H,total carbon,total nitrogen,ammonium nitrogen,nitrate nitrogen,total phosphorus,microbial biomass carbon and microbial biomass nitrogen in 0~30cm soil under the natural secondary near-mature forest of Pinus tabulaeformis.The water content,total carbon,total nitrogen,ammonium nitrogen,nitrate nitrogen,total phosphorus,microbial biomass carbon and microbial biomass nitrogen in the surface layer,shallow layer and middle layer all increased first and then decreased with the increase of forest density.The soil bulkdensity showed the opposite trend,and the p H value did not change Significantly,moderate density(925~1050trees?hm-2)helped maintain good soil structure and fertility.(2)The stand density had significant effects on the soil structure under different natural near-mature forests of Pinus tabulaeformis,and the influence from the surface layer to the middle layer was gradually reduced.The stand density had significant effects on soil moisture at different levels,and the influence from shallow to middle was gradually reduced.The effect of stand density on soil nutrients at different levels was significantly different,and the influence from the surface to the middle layer was gradually increased.(3)The vertical distribution law of soil property indexes under natural secondary near-mature forest of Pinus tabulaeformis was that the water content,total carbon,total nitrogen,ammonium nitrogen,nitrate nitrogen,total phosphorus,microbial biomass carbon and microbial biomass nitrogen in soil decreased with the increase of soil depth,while soil bulk density and p H value showed an opposite trend.The stand density had no significant effect on the overall pattern of vertical distribution of soil properties,but the medium density was more significant for the improvement of 0~30cm soil.(4)When the natural secondary near-mature forest of Pinus tabulaeformis was moderately dense,the water content,bulk density,total carbon,total nitrogen,ammonium nitrogen,nitrate nitrogen,total phosphorus,microbial biomass carbon and microbial biomass nitrogen in soil at a depth of 0~30cm remained relatively high,water conditions,ventilation conditions,carbon fixation levels,nitrogen release capacity,and microbial activity levels were better.