Spatial Distribution Of Fine Root Biomass And Morphological Characteristics Of Poplar Plantation With Different Density Configuration

Stand density and plant allocation are important measures for the management of artificial forest ecosystem,as well as important means for regulating the production of above-ground and underground parts of trees.Four poplar plantations with different densities and plant configurations(plant spacing×row spacing 3 m×8 m,5 m×5 m,6 m×6 m and 4.5 m×8 m,respectively)were selected as the research objects.The spatial distribution and seasonal dynamics of fine root biomass,fine root morphology and carbon and nitrogen content were studied by root drilling method,and the spatial distribution and seasonal dynamics of fine root biomass and morphological characteristics of poplar were analyzed.Discussing the response of fine root growth of poplar plantation to stand density and plant allocation pattern is of great significance for optimizing management measures of plantation ecosystem.The results show that:(1)In vertical direction,the fine root biomass,root length density and root surface area density of four densities and row spacing allocation stand(3 m×8 m,5 m×5 m,4.5 m×8 m,6 m×6 m)showed a significant decreasing trend with the increase of soil depth,while the specific root length was higher in surface(0-10 cm)soil and deep(40-50 cm)soil,but smaller in middle soil.Fine root biomass,root length density and specific root length of low-density stand were significantly higher than those of high-density stand,and mainly reflected in surface fine roots.Root surface area density was significantly higher in low-density forests than in high-density forests,but the specific surface area and root surface area density of fine roots were significantly higher in 6 m×6 m and 3 m×8 m forests in the middle and lower layers.The carbon content of fine roots in the surface layer was significantly higher;the carbon and nitrogen content and C/N ratio of fine roots in different diameter classes were different,showing that with the increase of diameter classes,the carbon content and C/N ratio of fine roots gradually increased,and the nitrogen content gradually decreased;the stand density had a significant impact on the carbon and nitrogen content distribution of fine roots,and the carbon content of fine roots in 10-20 cm soil layer was 4.5 m×8 m stand was significantly smaller than the other three stands.(2)In horizontal direction,the effects of different densities and allocation of stands on fine root biomass distribution were not consistent.There was a significant negative correlation between fine root biomass and sampling distance in rectangular configuration(3 m×8 m and 4.5 m x 8 m),but no significant correlation between fine root biomass and sampling distance in square configuration(5 m×5 m and 6 m×6 m).There was a significant positive correlation between specific surface area and sampling distance,but there was no significant correlation between root length density,specific root length and root surface area density and sampling distance.The horizontal distribution of fine root carbon content in different densities showed a trend of decreasing first and then increasing with the increase of distance from tree trunk.The carbon content of fine roots at 0.5 m,1 m,1.5 m and the carbon-nitrogen ratio of fine roots at 1.5 m were significantly higher in low-density stands.(3)The fine root biomass,root length density,specific root length and specific surface area in the direction of plant spacing were always significantly lower than those in the direction of row spacing.The fine root biomass and specific root length at the midpoint of plant spacing were always higher than those at the position of adjacent root piles,but there was no significant difference in root length density,root surface area density and specific surface area.Density management has a significant impact on the spatial distribution of fine root biomass and morphology in Poplar Plantation ecosystem,which is more reflected in surface fine roots(0-10 cm)and small diameter fine roots(< 0.5 mm).The arrangement of rectangular plants directly affects the horizontal distribution of fine roots,and has a significant impact on fine root biomass and morphology.(4)The biomass and morphology of fine roots of poplar showed obvious seasonal dynamics,and the biomass of fine roots of stand with different densities showed a single peak seasonal variation,with a peak in May;the seasonal dynamics of specific root length and root length density were basically consistent with biomass,but the specific surface area and root surface area density of fine roots of different stand densities were significantly different.The peak of specific surface area of fine roots of stand with 3 m×8 m and 4.5 m×8 m was in September.The peak values of 5 m×5 m and 6 m×6 m stand in May,3 m×8 m and 4.5 m×8 m stand in May and September,and the peak values of 5 m×5 m and 6 m×6 m stand in May and 4.5 m×8 m stand in May were single peak.