林分密度对水曲柳人工林吸收根生物量和根长密度的影响

Influence of Stem Density on Absorptive Root Biomass and Length Density in Fraxinus mandshurica Plantation

采用根钻法,研究了株行距分别为1.0 m×1.0 m、1.5 m×1.5 m、2.0 m×2.0 m 3种林分密度对水曲柳（Fraxinus mandshurica）人工林不同直径等级（≤0.5、〉0.5~1.0、〉1.0~2.0 mm）根系、特别是吸收根（直径≤0.5 mm）生物量和根长密度及其垂直分布的影响。结果表明：单位面积吸收根生物量随林分密度降低而减少,总细根（直径≤2.0 mm）生物量随林分密度降低而增加。吸收根与总细根根长密度均以中等林分密度下最高。单株水平上,各直径等级根群生物量和根长密度均随着密度的降低而增加。底层（〉20~30 cm）吸收根所占整个取样剖面的比例,随着吸收根根长密度的增加而降低。相同密度处理内各样地单位面积根系生物量和根长密度变异较大,导致密度的影响未达到显著性水平,但是根系直径等级和土壤深度对林分和单株细根指标均有显著影响（P〈0.05）。总之,林分密度对水曲柳人工林吸收根生物量和根长密度现存量影响较弱,而对其垂直分布格局的影响较强。

We used soil core method to determine how stem density （ 1.0 m× 1.0 m, 1.5 m× 1.5 m, and 2.0 m×2.0 m） affects the fine root biomass and length density of different diameter size classes, in particular of absorptive root （diameter ≤ 0.5 mm） , as well as the vertical distribution. The absorptive root biomass per unit area decreased with stem density decrea- sing, and total fine root （diameter≤2.0 mm） biomass increased with stem density decreasing. The highest length density of absorptive roots in absorptive and total roots both occurred in the intermediate stem density. At per tree level, root biomass and length density of all diameter size classes increased with stem density decreasing. The proportion of absorptive roots at the deep layer （20-30 cm） decreased with the length density of absorptive roots increasing. As large variation within each treatment, stem density had no significant on root traits, however, root diameter size classes and soil depth both had signif- icant influence on root biomass and length density at per area or per tree levels. The stem density had more significant effect on the vertical distribution of root biomass and length density than their standing crops.