【目的】研究不同栽植密度与植株配置形状下杨树人工林细根生物量在生长季中的动态变化,了解人工林地下生理生态过程(尤其是根系效应)的响应规律,为合理调控杨树人工林栽植密度并提高人工林地上部分生产力提供参考。【方法】选取栽植年份为10 a的杨树人工林作为试验林分,设置两种密度(低密度株行距:6 m×6 m和4.5 m×8 m。高密度株行距:5 m×5 m和3 m ×8 m)和两种栽植形状(正方形配置株行距:6 m×6 m和5 m×5 m。长方形配置株行距:4.5 m×8 m和3 m×8 m)共4个处理,每种密度和配置设置3个重复,共计12块样地。在每块样地中随机选取2株树,利用完整土块法在距树干60 cm处进行根系取样。分析比较细根[直径(d)≤2 mm]总生物量、不同直径等级(每0.5 mm为1个直径等级)细根生物量和生长季不同月份(5、7、9、11月)的细根生物量在不同密度和植株配置形状处理下的差异。【结果】①林分密度对细根总生物量的影响并不显著,但对生长季中前期(5、7月)细根生物量和小直径细根(d≤1 mm)生物量具有显著影响,生长季前期的小直径细根生物量均表现为高密度林分高于低密度林分;林分密度对细根生物量的影响效应在两种植株配置方式下具有相似的规律。②植株的配置形状对细根生物量具有显著的影响,但因不同生长阶段和林分密度而有所差异。总体上,正方形配置(5 m×5 m和6 m×6 m)的林分细根生物量要高于长方形配置(3 m×8 m和4.5 m×8 m)的细根生物量(除9、11月的低密度林分),尤其是在5月和7月的细根生物量和小直径细根生物量;③在不同植株配置形状中,正方形配置(5 m×5 m和6 m×6 m)的林分均匀度较高,细根生物量在株间与行间方向上并无显著差异;而长方形配置(3 m×8 m和4.5 m×8 m)的林分在株间与行间方向上细根生物量存在显著差异,且两种长方形配置的林分细根生物量在株行距方向上有截然相反的变化,4.5 m×8 m的林分行间方向的细根生物量比株间方向的高,而3 m×8 m林分的行间方向上的细根生物量比株间方向的低。【结论】林分密度和植株配置形状在整个生长季对细根总生物量没有显著影响;林分密度和植株配置形状都对小直径细根生物量存在显著影响,主要表现在生长季细根快速生长的5—7月;正方形配置方式更有利于杨树细根的生长,细根能充分占据利用土体空间,而长方形配置在一定程度上会造成根系挤压或竞争,同时造成土地浪费。

【Objective】 This study aimed to investigate changes in poplar fine-root biomass under different planting densities and spacing configurations and compare any differences. We explored the effects of density regulation and plant spacing on fine-root biomass to understand the response of physiological and ecological processes (especially root effects) in plantations and provide a scientific reference for rational regulation of poplar plantation density and improvement of aboveground productivity.【Method】 Poplar plantations with a stand age of 10 years were selected, and a total of four treatments with two planting densities (low density: 6 m × 6 m and 4.5 m × 8 m; high density: 5 m × 5 m and 3 m × 8 m) and two spacing configurations (square configuration: 6 m × 6 m and 5 m × 5 m; rectangle configuration: 4.5 m × 8 m and 3 m × 8 m) were set up. In total, 12 plots were selected with three replicates for each treatment. Two trees were randomly selected in each plot. Tree roots were sampled at 60 cm from the trunk in two directions using the intact soil-block method. We analyzed differences in total fine-root ( d ≤ 2 mm) biomass, fine-root biomass with different diameter grades (each 0.5 mm increment is a diameter grade), and fine-root biomass at different months under different planting densities and spacing configurations using repeated measures analysis of variance. 【Result】 ① There was no significant difference in total biomass between the high and low planting density stands, but there was a significant difference in the 0-1 mm diameter level in the early stage of the growth season (May-July), with the biomass of low diameter fine roots in the early stage of the growth season being greater in higher density stands than in lower density stands. The effect of spacing configurations on fine-root biomass showed a similar pattern. ② Different spacing configurations led to significant differences in fine-root biomass, which varied with growth stage and stand density. In general, the fine-root biomass in the square configurations was higher than that in the rectangular configurations, except for the fine-root biomass of low density stands in September and November but especially for the low diameter fine-root biomass at the early stage of the growth season (d ≤ 1 mm, May-July). ③ The fine-root distribution in square configurations was relatively even; there were no significant differences in spacing between plants and rows in the square configurations. However, there were significant differences in spacing between plants and rows in the rectangular configurations, but the biomass differences in the 3 m × 8 m and 4.5 m × 8 m plantations showed the opposite pattern. The inter-row differences in the fine-root biomass in the 4.5 m × 8 m forest were greater than the inter-plant differences, whereas the inter-row differences in the 3 m × 8 m forest were lesser than the inter-plant differences. 【Conclusion】 The effects of planting density and spacing configuration reflected neither in the total fine-root biomass nor in the entire growth season. Planting density and spacing configuration only have a significant effect on the biomass of fine roots with small diameter grades, especially in the early stage of the growth season, i.e., from May to July. The square configuration is more conducive to the growth of fine roots. Fine roots more efficiently make use of resources, and to a certain extent, rectangular configurations cause root compression or intense competition for limited resources, as well as wasting of land. In the future, we should further study the relationship between fine-root biomass and stand productivity, fully integrate aboveground and belowground ecosystem processes, fully understand the impact of planting density and spacing configuration on the productivity of plantations, and provide technical support for the improvement of plantation productivity.