In forests, ephemeral fine root tissues function to absorb nutrients and host mycorrhizal symbioses. Few broad studies have examined variation in the structure of roots and implications for root function, especially in forest communities. We sampled roots from 25 co-existing Northeastern U.S. woody species forming two of the most common types of mycorrhizae (AM and EM). For each species we quantified branching intensity, specific root length (SRL), diameter, tissue density, total phenolic concentration, and nitrogen concentration from samples collected in mature forests. Additionally for eight species, we quantified mycorrhizal colonization. Data analyses included phylogenetically-informed (PIC analyses, parsimony) and ahistorical (correlation and multivariate statistics) approaches.

Results/Conclusions

Among-species differences in branching intensity and SRL accounted for the greatest overall variation in root traits. Species forming AM generally had less branching intensity, lower SRL, thicker diameter and higher N concentration than those forming EM. Among both AM and EM species, mycorrhizal colonization decreased with SRL (r = -0.65), and was stronger when phylogenetically informed (r = -0.83), suggesting a trade-off between root morphology and colonization. Variation in SRL mapped moderately along phylogenetic lines (CI = 0.44), with inconsistencies interpretable in light of species’ ecophysiological differences that potentially affect belowground competition for resources. Patterns in root trait diversity suggest selection pressures have acted differently on AM and EM trees to shape morphological and architectural traits. Furthermore, variation in SRL associated with varying mycorrhizal colonization suggests trade-offs in nutrient acquisition strategies between species heavily dependent versus less-dependent on mycorrhizal fungi with potential ecological implications.