Identifying roots of northern hardwood species: patterns with diameter and depth

Abstract

Forest canopies are often stratified by species; little is known about the depth distribution of tree roots in mixed stands because they are not readily identified by species. We used diagnostic characteristics of wood anatomy and gross morphology to distinguish roots by species and applied these methods to test for differences in the rooting depth of sugar maple (Acer saccharum Marsh.), American beech (Fagus grandifolia Ehrh.), and yellow birch (Betula alleghaniensis Britt.) in two northern hardwood forests. We also distinguished hobblebush (Viburnum lantanoides Michx.) and white ash (Fraxinus americana L.) roots. Analysis of plastid DNA fragment lengths confirmed that 90% of the roots were correctly identified. The vertical distribution of fine roots of these species differed by 2-4 cm in the median root depth (P = 0.03). There was a significant difference in the distribution of roots by size class, with fine roots (0-2 mm) being more concentrated near the soil surface than coarser roots (2-5 mm; P = 0.004). The two sites differed by <2 cm in median rooting depths (P = 0.02). The visual identification of roots for the main tree species in the northern hardwood forest allows species-specific questions to be posed for belowground processes.Résumé : La stratification des essences est fréquente dans le couvert forestier. La distribution verticale des racines des arbres est peu connue dans les peuplements mélangés parce que l'identification des racines n'est pas facile. Nous avons utilisés les caractéristiques diagnostiques de l'anatomie et de la morphologie grossière du bois pour différencier les racines selon l'espèce et nous avons appliqués ces méthodes pour tester les différences de profondeur d'enracinement de l'érable à sucre (Acer saccharum Marsh.), du hêtre d'Amérique (Fagus grandifolia Ehrh.) et du bouleau jaune (Betula alleghaniensis Britt.) dans deux forêts feuillues nordiques. Nous avons aussi distingué les racines de la viorne bois-d'orignal (Viburnum lantanoides Michx.) et du frêne blanc (Fraxinus americana L.). L'analyse de la longueur des fragments d'ADN des plastes a confirmé que 90 % des racines ont été correctement identifiées. La distribution verticale des racines fines étaient significativement différente selon l'espèce (P = 0,03) et la différence variait de deux à quatre cm en comparant la profondeur médiane des racines. Il y avait une différence significative dans la distribution des racines selon la classe de dimension : les racines fines (0-2 mm) étaient plus concentrées près de la surface du sol que les plus grosses racines (2-5 mm) (P = 0,004). La profondeur médiane d'enracinement différait de moins de deux cm entre les deux stations (P = 0,02). L'identification visuelle des racines des principales espèces d'arbres dans la forêt feuillue nordique permet de formuler des questions propres à chaque espèce au sujet des processus souterrains.[Traduit par la Rédaction]

Belowground insights into nutrient limitation in northern hardwood forests

“…Species of fine roots of the small size classes that we studied, even those of different mycorrhizal type, cannot be easily distinguished visually in these forests (Yanai et al 2008), and so we cannot directly answer that question in our study. It is likely that we detected responses by some species but not others, as the ability of plant roots to proliferate in response to nutrients, though widespread, is not a universal trait (Robinson 1994, George et al 1997.…”

Patterns in δ15N in roots, stems, and leaves of sugar maple and American beech seedlings, saplings, and mature trees

“…In a broad analysis of over 30 sites across the northeastern US, Pardo et al (2006) proposed that a likely cause for species differences in foliar d 15 N (higher d 15 N in BE compared to SM) was differences in rooting depth. Since soil d 15 N increases with depth at the HBEF (Pardo et al 2001(Pardo et al , 2002, it is expected that the d 15 N of available soil N would also increase with depth and cause plants that get their N from deeper horizons, such as BE to have higher tissue d 15 N than SM, which is more shallow rooted (Yanai et al 2008 (Mariotti et al 1982;Nadelhoffer and Fry 1994). Inherent in this assumption is that there is no fractionation on uptake, storage, transport, and retranslocation of N (Nadelhoffer and Fry 1994 15 N values for a given species within a given site (Pardo et al 2006;Templer et al 2007).…”

Use of near-infrared reflectance spectroscopy to predict species composition in tree fine-root mixtures

“…Traditionally scientists resorted to hand-sorting methods with visual identification of species and fine-root vitality by using morphological criteria, such as color, diameter, branching order and root tips, etc. (Hölscher et al 2002;Schmid 2002;Yanai et al 2008). However, this method is very time-consuming, user dependent, and often subject to error (Roumet et al 2006).…”

“…Molecular genetic techniques have been used to accurately identify the species identity of fine roots (Brunner et al 2001;Jackson et al 1999;Mommer et al 2008). However, the costs of applying this method would be prohibitive when used to investigate belowground competitive interactions, which requires analysis of large numbers of samples (Yanai et al 2008).…”