Patterns in root trait variation among 25 co‐existing North American forest species

Abstract

Summary• Ephemeral roots have essential roles in plant and ecosystem functioning. In forests, roots account for a major component of carbon cycling, yet few studies have examined ranges of root trait variation and how different species vary in root form and function in these communities.• Root branching intensity, specific root length (SRL; root length per unit dry mass), root diameter, tissue density, phenolic concentration and nitrogen concentration were determined for the finest two root orders of 25 co-existing North American woody species sampled from mature plants in a single forest community. Trait correlations and multivariate patterns were examined to evaluate the most important trait differences among species.• Branching intensity, SRL, and phenolic concentration varied most widely among species (coefficient of variation (CV) = 0.42, 0.57 and 0.58, respectively). Species predominately forming ectomycorrhiza (EM) had a higher branching intensity than those forming arbuscular mycorrhiza (AM) with mycorrhizal types correctly predicted in c. 70% of individual observations by branching intensity alone. There was notably no correlation between SRL and nitrogen. Variation in SRL among species mapped partially along phylogenetic lines (consistency index (CI) = 0.44), with remaining variation attributable to differences in species' ecological specialization.• Variation found in root traits suggests different nutrient acquisition strategies within this community, which could have potential species-level effects on carbon and mineral nutrient cycling. Key words: arbuscular mycorrhiza (AM), comparative biology, ectomycorrhiza (EM), root architecture, root ecology, root morphology, specific root length (SRL). IntroductionBelowground systems remain one of the most poorly understood areas in terrestrial ecology. While the importance of fine root functions in these systems is recognized, understanding of root trait variation and its effects on ecological processes remains limited (Westoby & Wright, 2006). The effects of plants on ecosystem processes have been partly attributed to variation in leaf traits (Reich et al., 1999(Reich et al., , 2005 and mycorrhizal symbioses (Cornelissen et al., 2001). Broad investigations have found convergent patterns of leaf trait co-variation and trade-offs in functions among species (Reich et al., 1999), but investigations of root traits are still few and focused almost entirely on herbaceous species (e.g. Craine et al., 2002;Levang-Brilz & Biondini, 2003;Tjoelker et al., 2005;Roumet et al., 2006). In forest communities, ephemeral fine roots were found to show extensive trait diversity in a few studies that examined trait co-variation (Brundrett et al., 1990;Reich et al., 1998b;Pregitzer et al., 2002; Withington et al., 2006) or linked patterns of variation to plant growth strategies (Comas et al., 2002;Comas & Eissenstat, 2004). Critical questions remain as to whether general trade-offs exist among root traits of woody species, and whether these are linked to different plant strate...

Complex trait relationships between leaves and absorptive roots: Coordination in tissue N concentration but divergence in morphology

“…Indeed, compared with chemical traits, leaf and root morphological traits have been shown to be more phylogenetically conserved in this and previous studies (e.g., Kong et al., 2014; Li et al., 2015). Such strong phylogenetic effect acting on plant traits may explain why some trait correlations were strongly supported by early data collected from closely related species (e.g., Comas & Eissenstat, 2009; Fort, Jouany, & Cruz, 2013). Therefore, it is imperative to include phylogenetic considerations in the discussion of trait variation from the ecological to biogeographic scale and trait correlations at the whole‐plant level.…”

“…(2002). Here, we focused only on the most distal roots (i.e., the first‐order roots) and defined them as absorptive roots, as only the most distal first‐order roots with the most rapid turnover and highest metabolic activity are functionally comparable to leaves as resource acquisition organs (Comas & Eissenstat, 2009; Guo et al., 2008; Kong et al., 2014). Also, to ensure a fair comparison between plant types, the first‐order root was considered both for woody and nonwoody species.…”

Root structure–function relationships in 74 species: evidence of a root economics spectrum related to carbon economy

“…The development of a unified framework toward an RES might suffer from a lack of homogeneity in fine-root sampling methods between studies. Because it is now recognized that fine-root structure and function vary among fineroot orders both within (Pregitzer et al, 2002;Guo et al, 2008;Valenzuela-Estrada et al, 2008;Comas & Eissenstat, 2009;Picon-Cochard et al, 2012;McCormack et al, 2015) and across species (McCormack et al, 2012), the comparison of results obtained with contrasting sampling methods might bias general patterns of root traits. This issue is particularly relevant for the comparison between woody and nonwoody species, since root traits are commonly measured on first-order roots in woody species and on roots < 2mm in herbaceous species (G. Freschet et al, unpublished).…”

Scientific Opinion on good modelling practice in the context of mechanistic effect models for risk assessment of plant protection products

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