| Fine root is an important organ for water and nutrient uptakes in woody plants,meanwhile,fine root production and turnover are significant to nutrient cycle and carbon allocation in terrestrial ecosystems.Stand density have an important influence on forest productivity and ecosystem stability.However,the effects of stand density on fine root have been paid less attention in most previous studies.Therefore,detailed research on how stand density influence fine root biomass,production,turnover,and spatial distribution 1s not only important for improving forest productivity,but also benefit for us to deeply understand the related nutrient cycling and carbon flow in forest ecosystems.In this study,we quantified the relationship between fine root characteristics and stand density(Treatment S1:3572 stem·ha-1,Treatment S2:3128 stem ha-1,Treatment S3:2336 stem·ha-1,Treatment S4:1468 stem·ha-1)in Manchurian ash(Fraxinus mandschurica)plantation in Northeastern China.We employed Soil core method to determine fine root biomass and spatial distribution,and used Ingrowth core to estimate fine root production and turnover.The results were as follows:(l)Stand density had a significant effect on fine root biomass and length density.The total root(diameter ≤2.0 mm,soil layer ≤30 cm)and absorptive root(diameter ≤0.5 mm,soil layer≤30 cm)biomass and length density per unit area increased significantly with stand density decreasing,and the total fine root biomass increased from 274.14 to 385.·l g*m"2.At tree level,fine root biomass and length density of all diameter size classes increased significantly with stand density decreasing.Vertical distribution of fine root biomass and length density varied significantly in different stand densities at both per unit area and per tree level.The proportions of absorptive root biomass and length density of-surf’ace soil layer accounted for the whole soil profile were 57.43%to 67.42%and 61.92%to 68.45%,respectively,and had a tendency of increasing with stand density decreasing.(2)Fine root production and turnover varied significantly in different stand densities.Fine root production of-all diameter size classes increased with stand density decreasing at per unit area and per tree level,particularly,the fine root(diameter<1.0 mm)exhibiting a significant differences,and the total fine root(diameter<2.0 mni)production(0 to 30 cm soil depth)changed from 84.27 to 184.56 g·m一2 and 269.38 to 1256.72 g stem".Absor tive root production decreased with soil layer decreasing in both area and tree terms of all diameter size classes and all stand density levels.Fine root turnover increased with stand density decreasing,and significant differences were found in root of diameter 0.5 um to 1.0 mm.Fine root turnover decreased significantly with diameter size classes increasing in all the soil layers and stand density levels.Moreover,the fine root turnover increased significantly with soil layers increasing in all the diameter size classes and stand density levels.(3)The response of spatial distribution of fine root biomass to stand density was different.The horizontal distribution pattern of total root(diameter<2.0 mm,soil layer:5:30 cm)biomass were different in each stand density treatment.The root biomass of different horizontal distances were similar to each other in S1 treatment;the root biomass was higher when the sampling location closer to trunk in S2 treatment;the root biomass increased with the distances of sampling location to trunk increasing in S3 treatment;the root biomass in S4 treatment distributed irregular with the distances of sampling location to trunk increasing.In treatment of S1,S3,S4,the absorptive root biomass increased with the distances of sampling location to trunk increasing at surface soil layer,but the trend was opposite in S2 treatment.In addition,biomass of absorptive root and diameter from 0.5 mm to 1.0 mm root decreased significantly with soil layer decreasing at all stand density levels and horizontal distances. |
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