Effect Of Root System On Soil Properties

This paper investigated the root distribution and the corresponding mechanical, physical and chemical properties of roots at each soil layer in the woodland Covered with Pinus tabulaeformis and Quercus variabilis at Beijing Jiufeng National Forest Park, by using sample plots excavation and indoor experimental determination and analysis. Our work identified the role of root system in soil conservation, and the improvement of physical and chemical properties to soil by plant roots, according to these survey results, we draw the following conclusions.(1)The overall trend was that root biomass of each diameter class reduced layer by layer for Pinus tabulaeformis and Quercus variabilis, and the root biomass of each diameter class in the surface(0～30 cm) was higher than in the subsoil significantly; we also discovered that the roots in diameter greater than 5mm were dominant in most cases; besides, the roots in diameter of 0-2 mm distributed in each soil layer for the both of two species, there was exponential relationship between the biomass of roots with 0-2mm diameter in each soil layer and the depth of soil; the total root biomass of each soil layer also had exponential function relationship with depth of soil.(2)The cohesive force of plain soil increased with the depth of soil, but the internal cohesion of the soil which mixed with roots decreased with increasing soil depth because of reduction of root biomass layer by layer, exactly the opposite to the plain soil; The soil cohesive force had a positive linear relationship with roots content and the depth of soil; The internal friction angle of plain soil and root-soil composites changed with the increase of soil depth slightly and irregularly. With the deepening of the soil and reducing of root biomass, the soil cohesive force with different series of root content showed a decreasing trend layer by layer; the cohesive force of deeper soil was smaller than the upper soil because of the decreasing root content, but when the added root biomass was similar, the internal cohesion of the root-soil composites was larger in the deep soil than shallow soil; The soil cohesive force had positive correlation with the roots content in soil, but the internal friction angle of different series of root content changed little, and had no significant variation law.(3)The moisture content of soil had the most significant correlation with the biomass of roots in 2-5 mm diameter class in each soil layer for Pinus tabulaeformis and the total root biomass in each soil layer for Quercus variabilis; The organic matter produced by roots could effectively reduce the soil bulk density, so the soil bulk density decreased with the reduction of the root biomass in soil; The soil non-capillary porosity, capillary porosity and total porosity decreased with the reduction of root biomass, which was due to the mechanical interludes of roots; The main effect of roots on soil particle diameter composition was the increase of small particulate matter content which was less than 0.02 mm in diameter.(4)The roots of Pinus tabulaeformis and Quercus variabilis had cumulative effect on chemical nutrient content in each forest soil layer, the content of soil nutrient such as soil organic matter, total nitrogen, available nitrogen, total potassium and available potassium decreased with the deepening of soil; The content of total nitrogen and available nitrogen, total potassium and potassium in the surface soil of 0-10 cm was higher than that in the underlying soil significantly, but the difference of organic matter, total nitrogen, available nitrogen, total potassium and available potassium in deeper soil was obscure. With the deepening of soil layer, there was a small change of the content of total phosphorus and available phosphorus among each soil layer, the change law of the content of total phosphorus and available phosphorus for both Pinus tabulaeformis and Quercus variabilis woodland was not obvious.(5)There were three main effects of root system on soil properties:the impact of root mechanical and physical characteristics; the impact of organic matter produced by roots; the impact of soil biological activity aggregated in root influenced zone.