| Thinning promotes the growth of trees by reducing the density of forests,releasing trees’growth space,improving environmental conditions such as light and soil.Previous studies have paid more attention to the mean growth of residual trees under different thinning intensities,but the relative growth space size of the residual trees under the same thinning intensity are not consistent.There may be differences in the response of residual trees with different growth release degrees to thinning.Studies have found that the greater the degree of growth release of residual trees,the greater of the above-ground growth.However,fine roots,as the main organ for obtaining soil resources,how to respond is unclear.In addition,the decomposition and nutrient release of stumps affect the growth of fine roots in the surrounding soil.However,there is little knowledge about how the fine roots of forest trees respond to the stump under different growth release gradients.In such case,this study was conducted in the 49-year-old irregular mixed forest of Fraxinus mandshurica and Larix olgensis under 50%thinning intensity to cut L.olgensis in Mengjiagang Forest Farm in Jiamusi City,Heilongjiang Province.In the two consecutive growing seasons from 2019 to 2020,morphology(divided into first order root,second order root and transport fine root,0-10 cm)and biomass and length density(diameter≤2 mm,0-30 cm)fine roots of F.mandshurica under three growth release gradients(low:Ⅰ,moderate:Ⅱ,and high:III)were studied.And compared and analyzed the impact of stump to fine root under three growth release gradients.The mean purpose was to reveal the influence of the growth release gradient(Ⅰ～Ⅲ)after thinning and stump on the resources acquisition strategy of fine root.The results of the study as follows:(1)The morphology of fine roots of F.mandshurica were significantly affected by the growth release gradient.In each root categories,the fine root diameter and tissue density incresed and the specific root length decreased with increasing growth release gradient.Compared with the first year after thinning(2019),in the second year(2020),the fine root diameter of each root categories under three growth release gradients decreased,and the tissue density increased.However,the specific root length decreased only under moderate release gradient,and generally increased under both low and high release gradient.The significant differences in the morphology of fine roots between different growth release gradients were mainly reflected in the absorptive roots(first order root,second order root).Although the morphology of the fine roots of F.mandshurica under three growth release gradients were not significantly different with or without the effects of stump.However,the existence of stump had an influence on the inter-annual changes of fine root morphology,and this influence was related to the growth release gradients.Compared with the first year after thinning,the fine root diameter of each root categories of F.mandshurica under three growth release gradients decreased in the second year after thinning without stump.The diameter of fine roots responded more strongly under high release gradient,and the diameter of each root categories was significantly reduced.With the effects of stump,although the absorptive root diameters under the three growth release gradients were also reduced,they reached the significant level under low release gradient.In addition,the diameters of the transport roots under moderate and high release gradient were both thicker.Specific root length was strongly affected by stump under high release gradient.The specific root length of each root categories increased without the effects of stump,but decreased with the effects of stump;The tissue density of the absorptive roots of each release gradient increased with or without the effects of stump,but it was not significant without the effects of stump,and generally reached a significant level with the effects of stump.(2)Fine roots biomass of F.mandshurica differed between different growth release gradients.In each soil layer,fine roots biomass under low release gradient was the largest,and the difference reached a significant level on the surface soil layer.In the second year after thinning,as the growth release gradient increased,the proportion of F.mandshurica fine root biomass allocated to the surface soil layer(0-10 cm)decreased(69.7%,64.2%and 61.4%).The proportion of subsurface soil layer(10-20 cm)increased(26.0%,31.1%and 34.1%).The proportion of the deep soil layer(20-30 cm)was not much different(4.1%,5.0%and 4.5%).Compared with the first year after thinning,the proportion fine roots biomass of F.mandshurica to the total biomass of fine roots of F.mandshurica and L.olgensis in each soil layer of the three growth release gradients increased in the second year after thinning.In addition,in all soil layers,the proportion fine roots biomass of F.mandshurica was the highest(92.4%,80.4%,67.7%)of low release gradient.The effect of stumps on the fine roots biomass of F.mandshurica was related to the growth release gradient.However,compared with the condition of no stump,the existence of stump made the biomass of fine roots in the surface soil layer of F.mandshurica higher under low release gradient,and lower in the subsurface and deep layers of soil under moderate and high release gradient.Therefore,with the effects of stump,there were significant differences in the fine root biomass between the growth release gradients in each soil layer.In addition,compared with the condition of no stump,stump resulted in a higher proportion of fine root biomass in the surface soil layer of F.mandshurica under moderate and high release gradient.However,the porprotion of fine root biomass in each soil layer under low release gradient had no differences with or without stumps.Compared with the condition of no stump,the porprotion of fine root biomass of F.mandshurica to the total biomass of the fine roots of F.mandshurica and L.olgensis was lower.(3)The fine root length density of F.mandshurica was affected by the growth release gradients,and the significant impact appeared in the surface soil layer.The low release with the lowest growth release has the largest fine root length density,and the difference between it and the moderate release is significant.Root length density was the largest under low release gradient,and the difference between low and moderate release gradient was significant.In the second year after thinning,as the growth release gradient increased,the proportion of fine root root length density of F.mandshurica allocated to the surface soil layer decreased(75.0%,65.6%,63.8%),and the proportion of subsurface and deep soil layers increased.Compared with the first year after thinning,the porprotion of the fine root length density of F.mandshurica to the total length density of fine roots of F.mandshurica and L.olgensis in each soil layer under three growth release gradients increased in the second year after thinning.The poprotion was the highest under low release gradient in both the surface and subsurface soil layer,while the porprotion in the deep soil layer were similar.The effect of stumps on the fine roots length density of F.mandshurica was related to the growth release gradient.However,compared with the condition of no stump,fine root length density was the highest in the low released gradient in the surface soil layer with the effects of stump.Therefore,the difference in root length density of F.mandshurica in the surface soil layer with the effects of stump increased significantly among the growth release gradients.In addition,stump affected the inter-annual variation of the porprotion of the fine root length density of F.mandshurica in each soil layer,and there were differences due to different growth release gradients.Compared with the condition of no stump,the porprotion of the root length density of the fine roots of F.mandshurica to the total length density of the fine roots of F.mandshurica and L.olgensis with the effects of stump was lower.Overall,the morphology,biomass and length density of the fine roots of F.mandshurica were significantly different in the growth release gradient.The influence of stumps on the morphology,biomass and length density of fine roots was related to the growth release gradient.Some traits linked to the effect of the stump,but some did not.These findings not only enhance our understanding of how thinning affects the resources acquisition of fine root,but also provide a theoretical reference for the cultivation of high-quality big-diameter wood of F.mandshurica. |
PDF Full Text Request