毛白杨人工林吸收根判定阈值对其空间分布特征的影响

Influence of the determination threshold of absorbing roots on the spatial distribution characteristics of plantation poplar

通过林木根系研究中不同吸收根的判定标准下根系空间分布特征的差异对比,阐明根系分级标准对吸收根空间分布格局的影响,提升根系研究精度,明确林木根系有效“觅食”区域。在7年生毛白杨林分中于5株样树周围挖取780个土柱,选取根系形态指标:根系平均直径(RD)、根系表面积密度(RAD)、根长密度(RLD)和根系体积密度(RVD)研究其垂向与径向的分布动态,并分析不同吸收根判定标准对毛白杨细根空间分布以及各形态指标的影响。结果表明:选取2 mm作为吸收根判定标准确实会导致运输根被误判为吸收根,但其空间分布特征仍能反映吸收根的真实空间分布格局。而且在该判定标准下,判定标准对于实际的细根形态和空间分布情况是否会产生的影响由于监测指标的不同以及研究位置的变化而不同。其中RAD、RLD和RVD的空间分布特征基本相同,但RVD的差值比例远高于其他指标,且深土层的差值比例普遍高于浅土层。因此,以2 mm为吸收根判定标准时,选取RLD和RAD更能准确反映吸收根的真实空间分布格局,且该标准更适用于在进行相对较浅的土层中开展研究,采用2 mm为阈值划分吸收根研究细根垂直分布特征时建议以各形态指标在各个土层所占比例来进行描述。本研究仅针对毛白杨开展,研究结果在不同树种间是否存在普适性仍有待后续开展类似研究进一步验证。

The study compares the spatial distribution characteristics of root systems based on different absorption criteria to clarify the impact of root classification criteria on the absorbing root distribution pattern.This study aims to improve the accuracy of root studies,and to clarify the effective"foraging"regions of tree roots.In a 7⁃year⁃old Populus tomentosa plantation,780 soil columns were excavated around five sample trees.Root morphological indexes including root mean diameter(RD),root surface area density(RAD),root length density(RLD),and root volume density(RVD)were studied to observe their vertical and lateral distribution dynamics.The effects of different root absorption criteria on both the spatial distribution of fine roots and each morphological index of Populus tomentosa were also analysed.Results showed that choosing 2 mm as the criterion for absorbing roots would indeed lead to the transport roots being misclassified as absorbing roots,but their spatial distribution characteristics could still reflect the true spatial distribution pattern of absorbing roots.Moreover,under this criterion,the influence of the criterion on the actual shape and spatial distribution of fine roots was different due to the differences in monitoring index and study location.The spatial distribution characteristics of RAD,RLD,and RVD were basically the same,but the difference ratio of RVD was much higher than other indexes,and the difference ratio of the deep soil layer was generally higher than that of the shallow soil layer.Therefore,selecting RLD and RAD at the 2 mm criterion could more accurately reflect the true spatial distribution pattern of absorbing roots,and this standard was more suitable for conducting research in relatively shallow soil layers.When 2 mm was used as the threshold for studying the vertical distribution characteristics of fine roots by dividing the absorbing roots,it is recommended to describe the proportion of each morphological index in each soil layer.The current study was limited to Populus tomentosa,and the generalizability of the results across diverse tree species should be confirmed in future investigations.