Kirfel Kristina, Leuschner Christoph, Hertel Dietrich, Schuldt Bernhard
Plant Ecology, Albrecht von Haller Institute for Plant Sciences, University of GöttingenGöttingen, Germany.
Front Plant Sci. 2017 Jul 24;8:1194. doi: 10.3389/fpls.2017.01194. eCollection 2017.
Despite their importance for water uptake and transport, the xylem anatomical and hydraulic properties of tree roots have only rarely been studied in the field. We measured mean vessel diameter (), vessel density (VD), relative vessel lumen area (lumen area per xylem area) and derived potential hydraulic conductivity () in the xylem of 197 fine- to medium-diameter roots (1-10 mm) in the topsoil and subsoil (0-200 cm) of a mature European beech forest on sandy soil for examining the influence of root diameter and soil depth on xylem anatomical and derived hydraulic traits. All anatomical and functional traits showed strong dependence on root diameter and thus root age but no significant relation to soil depth. Averaged over topsoil and deep soil and variable flow path lengths in the roots, increased linearly with root diameter from ∼50 μm in the smallest diameter class (1-2 mm) to ∼70 μm in 6-7 mm roots (corresponding to a mean root age of ∼12 years), but remained invariant in roots >7 mm. never exceeded ∼82 μm in the 1-10 mm roots, probably in order to control the risk of frost- or drought-induced cavitation. This pattern was overlain by a high variability in xylem anatomy among similar-sized roots with showing a higher variance component within than between root diameter classes. With 8% of the roots exceeding average in their diameter class by 50-700%, we obtained evidence of the existence of 'high-conductivity roots' indicating functional differentiation among similar-sized roots. We conclude that the hydraulic properties of small to medium diameter roots of beech are mainly determined by root age, rendering root diameter a suitable predictor of hydraulic functioning, while soil depth - without referring to path length - had a negligible effect.
尽管它们对水分吸收和运输很重要，但树根的木质部解剖结构和水力特性在野外很少被研究。我们测量了197条直径从细到中等（1 - 10毫米）的树根木质部的平均导管直径（）、导管密度（VD）、相对导管腔面积（每木质部面积的腔面积），并推导了潜在水力传导率（），这些树根取自沙质土壤上一片成熟欧洲山毛榉林的表土和底土（0 - 200厘米），以研究根直径和土壤深度对木质部解剖结构和推导的水力特征的影响。所有解剖和功能特征都强烈依赖于根直径，进而依赖于根龄，但与土壤深度没有显著关系。在表土和深层土壤以及根内不同的流动路径长度上进行平均， 随着根直径从最小直径类（1 - 2毫米）的约50μm线性增加到6 - 7毫米根中的约70μm（对应平均根龄约12年），但在直径大于7毫米的根中保持不变。在1 - 10毫米的根中， 从未超过约82μm，这可能是为了控制霜冻或干旱引起的空化风险。这种模式被相似尺寸根之间木质部解剖结构的高变异性所覆盖， 在根直径类内显示出比类间更高的方差分量。8%的根在其直径类中超过平均 的50 - 700%，我们获得了“高传导率根”存在的证据，表明相似尺寸根之间存在功能分化。我们得出结论，山毛榉中小直径根的水力特性主要由根龄决定，使得根直径成为水力功能的合适预测指标，而土壤深度 - 不考虑路径长度 - 影响可忽略不计。
