Børja Isabella, De Wit Heleen A, Steffenrem Arne, Majdi Hooshang
Norwegian Forest and Landscape Institute, As, Norway.
Tree Physiol. 2008 May;28(5):773-84. doi: 10.1093/treephys/28.5.773.
We assessed the influence of stand age on fine root biomass and morphology of trees and understory vegetation in 10-, 30-, 60- and 120-year-old Norway spruce stands growing in sandy soil in southeast Norway. Fine root (< 1, 1-2 and 2-5 mm in diameter) biomass of trees and understory vegetation (< 2 mm in diameter) was sampled by soil coring to a depth of 60 cm. Fine root morphological characteristics, such as specific root length (SRL), root length density (RLD), root surface area (RSA), root tip number and branching frequency (per unit root length or mass), were determined based on digitized root data. Fine root biomass and morphological characteristics related to biomass (RLD and RSA) followed the same tendency with chronosequence and were significantly higher in the 30-year-old stand and lower in the 10-year-old stand than in the other stands. Among stands, mean fine root (< 2 mm) biomass ranged from 49 to 398 g m(-2), SLR from 13.4 to 19.8 m g(-1), RLD from 980 to 11,650 m m(-3) and RSA from 2.4 to 35.4 m(2) m(-3). Most fine root biomass of trees was concentrated in the upper 20 cm of the mineral soil and in the humus layer (0-5 cm) in all stands. Understory fine roots accounted for 67 and 25% of total fine root biomass in the 10- and 120-year-old stands, respectively. Stand age had no affect on root tip number or branching frequency, but both parameters changed with soil depth, with increasing number of root tips and decreasing branching frequency with increasing soil depth for root fractions < 2 mm in diameter. Specific (mass based) root tip number and branching density were highest for the finest roots (< 1 mm) in the humus layer. Season (spring or fall) had no effect on tree fine root biomass, but there was a small and significant increase in understory fine root biomass in fall relative to spring. All morphological characteristics showed strong seasonal variation, especially the finest root fraction, with consistently and significantly higher values in spring than in fall. We conclude that fine root biomass, especially in the finest fraction (< 1 mm in diameter), is strongly dependent on stand age. Among stands, carbon concentration in fine root biomass was highest in the 30-year-old stand, and appeared to be associated with the high tree and canopy density during the early stage of stand development. Values of RLD and RSA, morphological features indicative of stand nutrient-uptake efficiency, were higher in the 30-year-old stand than in the other stands.
我们评估了林龄对挪威东南部沙质土壤中10年、30年、60年和120年生挪威云杉林分中树木及林下植被细根生物量和形态的影响。通过取芯至60厘米深度的土壤样本，测定树木（直径<1毫米、1 - 2毫米和2 - 5毫米）和林下植被（直径<2毫米）的细根生物量。基于数字化根系数据，确定细根形态特征，如比根长（SRL）、根长密度（RLD）、根表面积（RSA）、根尖数量和分支频率（每单位根长或根质量）。与生物量相关的细根生物量和形态特征（RLD和RSA）随时间序列呈现相同趋势，30年生林分显著高于其他林分，10年生林分显著低于其他林分。林分间，平均细根（<2毫米）生物量范围为49至398克·米⁻²，SRL为13.4至19.8米·克⁻¹，RLD为980至11650米·毫米⁻³，RSA为2.4至35.4米²·米⁻³。所有林分中，树木的大部分细根生物量集中在矿质土壤上部20厘米和腐殖质层（0 - 5厘米）。10年生和120年生林分中，林下细根分别占总细根生物量的67%和25%。林龄对根尖数量或分支频率无影响，但这两个参数随土壤深度变化，直径<2毫米的根段，根尖数量随土壤深度增加而增加，分支频率随土壤深度增加而降低。腐殖质层中最细根（<1毫米）的比（基于质量）根尖数量和分支密度最高。季节（春季或秋季）对树木细根生物量无影响，但秋季林下细根生物量相对于春季有小幅显著增加。所有形态特征均表现出强烈的季节变化，尤其是最细根段，春季的值始终显著高于秋季。我们得出结论，细根生物量，尤其是最细部分（直径<1毫米），强烈依赖于林龄。林分中，30年生林分细根生物量中的碳浓度最高，这似乎与林分发育早期的高树木密度和冠层密度有关。作为林分养分吸收效率指标的形态特征RLD和RSA值，30年生林分高于其他林分。
