间伐对黄龙山油松中龄林细根空间分布和形态特征的影响

Effects of thinning intensity on fine root biomass and morphological characteristics of middle-aged Pinus tabulaeformis plantations in the Huanglong Mountains

为探究油松细根生长与抚育间伐的关系,以黄龙山林区4种不同间伐强度(对照,轻度,中度,强度)下的油松人工中龄林为研究对象,采用根钻法,分3层(0—20,20—40,40—60cm)获取细根样品,研究了间伐强度对油松细根生物量和形态特征的影响。结果表明:油松细根生物量主要分布在0—20 cm土层,不同间伐强度下细根生物量差异显著(P<0.05),随间伐强度的增大,细根生物量先升高后降低,强度间伐下0—20 cm土层细根生物量显著降低(P<0.05),20—40 cm土层和40—60 cm土层细根生物量所占比例随间伐强度的增大而增大。细根根长密度和根表面积密度在不同间伐强度和不同土层间均差异显著(P<0.05),且变化规律与生物量基本一致。细根比根长和比表面积随间伐强度的增加而增大,且强度间伐与其他强度呈显著性差异(P<0.05)。轻度和中度间伐对小径级细根(0—1.0 mm)有显著影响,对较大径级细根(1.0—2.0 mm)的影响则不显著(P<0.05),强度间伐对0—2.0mm的细根均有显著影响(P<0.05)。中度间伐(保留郁闭度0.7)条件下,油松林地细根总生物量达到最大1022.43 g/m2,此条件下细根的根长密度和根表面积密度也达到最大,能充分利用林地的立地资源,最有利于保留木的生长。

Pinus tabulaeformis plantations play an important role in local water and soil conservation and ecological protection in the Loess Plateau. Because of the large surface area, short life span, and rapid turnover, fine root systems were considered an important part in material cycling, energy transportation, and soil and water conservation of the forest ecosystem. This study was conducted in a middle-aged P. tabulaeformis plantation, located in the Huanglong Mountains, south of Loess Plateau, China. Thinning was performed on three occasions in 2008 following afforestation： light thinning, medium thinning, and heavy thinning. Three replicates of thinned and un-thinned treatments （20 m×30 m） were selected in our research. Basic data of fine root biomass and morphological characteristics were collected from three soil depths （0-20 cm, 20-40 cm, and 40-60 cm） via root drilling methods. The results showed that fine root biomass increased with increasing thinning intensity up to the medium thinning treatment and then decreased in the heavy thinning treatment. Fine root biomass in the 0-20cm soil layer decreased significantly （P 〈 0.05） under heavy thinning intensity compare with other treatments. The proportions of fine root biomass in the 20-40-cm and 40-60-cm soil layers increased with increasing thinning intensity. The differences in root length density and root surface area density between different thinning intensities and different soil layers were significant （P 〈 0.05）, and exhibited a similar trend as the fine root biomass. With increased thinning intensity, specific root length and specific surface area of fine roots increased, and the differences were significant under heavy thinning （P 〈 0.05）. Light and medium thinning had a significant effect on finest diameter fine roots （0-1.0 mm）, but no significant effect on fine roots （1.0-2.0 mm） （P 〈 0.05）, whereas heavy thinning had a significant effect on all roots （0-20 cm） （P 〈 0.05）. Fine roots may be distributed in the deep soil layer after thinning. Compared with fine roots, the finest ones were more sensitive to different thinning intensities. In this study, fine root biomass （1022.43 g/m2）, along with the root length density and root surface area, peaked at the medium thinning intensity, which could be the appropriate silviculture practice for tree growth.