| In this study,10-year-old poplar plantations were selected as experimental stands.Two plantingdensities(low density: 6m?6m and 4.5m?8m;high density: 5m?5m and 3m?8m)and two plant spacing configurations(square configuration: 6m?6m and 5m?5m;rectangular configuration: 4.5m?8m and 3m?8m)were set up.The dynamic changes of carbohydrate content,nutrient content,biomass and fine root morphology of fine roots with different diameter grades(0.5mm for one diameter grade)were measured.The effects of different density and row spacing on the dynamic characteristics of fine roots such as carbon,nutrient and biomass were discussed in order to understand the response of underground physiological and ecological processes of plantation to management measures such as density and allocation.Regularity has important scientific significance for improving the production of plantation and enhancing the capacity of carbon sequestration and sink increase of plantation.The main results and conclusions are as follows:1.There are significant differences in carbohydrate content of fine roots in different densities,configurations and months.The contents of soluble sugar,starch and NSC all increased first and then decreased with seasons.In the early growth season,the soluble sugar content of high and low density stands showed significant differences in different diameter grades,while in the late growth season,the effect of stand density on soluble sugar content was mainly concentrated in the diameter grade of 1<D?1.5mm;The square configuration and the rectangular configuration show an alternating trend throughout the growth season.Starch content in high density stands was higher than that in low density stands throughout the growth season.The square configuration and the rectangular configuration showed an alternating trend throughout the growth season.2.The contents of C,N and P in fine roots were significantly different among different densities,configurations and months.The variation of C and P content with seasons generally shows a zigzag upward trend,with the early growth season being lower than the late growth season,while the variation of N content with seasons is opposite to the variation of C content.The density and configurations have little influence on the C content of fine roots,mainly concentrated in the small diameter fine roots in the early growth season.The effect of configurations on the N content of fine roots is mainly concentrated in the small diameter fine roots in the middle of the growing season.the effect of density on the N content of fine roots is mainly shown in the diameter grades of 0.5 <D?1 mm and 1<D?1.5 mm in may,July and September.The P content of highdensity stands is higher than that of low density stands,while that of square configurations is higher than that of rectangular configurations.The effects of density and configurations on fine roots C/N,C/P and N/P are mainly concentrated in July and September,and different forest stands show inconsistent change rules.3.The response of root length of small diameter and fine root to density and configurations is not strong,mainly manifested in the root length of low density stand(4.5m?8m)is significantly higher than that of high density stand(5m?5m);However,the root system with larger diameter grade showed that the stand with square configuration was higher than that with rectangular configuration.The influence of density and configuration on the surface area of fine roots is mainly concentrated in the roots with larger diameter,and the square configuration is higher than the rectangular configuration as a whole.The influence of density and configuration on root length is also mainly concentrated on small diameter and fine root.The root length density of small-diameter fine roots is higher in low-density stands as a whole than in high-density stands,while that of large-diameter roots is higher in square stands as a whole than in rectangular stands.4.Stand density has a significant effect on the fine root biomass and small diameter fine root biomass in the middle and early growth season.The small diameter fine root biomass in the early growth season is higher in high density stands than in low density stands.The arrangement of plants has a significant effect on the fine root biomass,but there are differences due to different growth stages and different stand densities.In general,the fine root biomass of square stands is higher than that of rectangular stands.there were significant differences in the stands of rectangular configuration(3m?8m and 4.5m?8m)between spacing in plants and rows,but the biomass difference in 3m?8m and 4.5m?8m plantations was opposite. |
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