Linking fine root traits to maximum potential growth rate among 11 mature temperate tree species

Summary There is limited understanding of patterns of variation that exist among root traits of different species, especially under field conditions. We contrasted 11 fast‐ and slow‐growing species paired within five evolutionary lineages to investigate whether root traits associated with soil resource acquisition were related to species’ potential growth rate. Measurements of root morphology, architecture, nitrogen and phenolic concentration, respiration and phosphorus uptake were taken on fine, non‐woody roots sampled from forest stands in central Pennsylvania, USA. Across all five contrasts, roots of fast‐growing species generally had higher specific root length, smaller diameters, greater degree of branching, and lower phenolic concentrations than those of slow‐growing species. This suggests differences in potential soil exploration and root defences among species differing in potential growth rate. There were no significant differences between fast‐ and slow‐growing species in root tissue density, respiration or P uptake. Lack of root physiological differences between species differing in growth rate contrasted with previous research on chamber‐grown seedlings. These results imply that, while roots of fast‐growing species may be constructed for more rapid soil exploration and shorter life span than those of slow‐growing species, root physiology is either more closely tied to overall plant physiology, which is more similar among mature trees, or masked by variation in soil microsites, root age or interactions with mycorrhizal fungi.