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

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.