Fine root physiology, morphology, and construction among fast- and slow-growing woody species of the northeastern United States

Woody species that vary in growth rate are expected to have different requirements for nutrients and, thus, different strategies for acquiring nutrients. Comparisons of fine root morphology and physiology were made between a fast- and a slow-growing species within maple, oak, and pine families to examine variation in root traits associated with plant growth rate on 1-yr-old seedlings growing in a growth chamber. Across all families, fine roots of fast-growing species had greater SRL, thinner diameters, and faster respiration than those of slow-growing species. Fine roots of fast-growing species of maple and oak had faster P uptake on a surface area basis than those of slow-growing species, whereas little difference in P uptake was found between pine species. On a dry weight basis, nitrogen concentrations were higher, carbon:nitrogen ratios lower, and root tissue construction costs higher in fast- than slow-growing maple and oak (data were unavailable for pines). Differences in tissue density were not significant between fast- and slow-growing species across families (P = 0.17).; Next, comparative approaches were used to examine the roots of 25 diverse woody species collected from mature forests. Nine root traits were examined that were related to root morphology, branching structure, chemical defenses, nutrient uptake and metabolic activity. Examination of root traits and life history characteristics indicated that root morphology (especially SRL) and architecture (tip density) were correlated with plant evolutionary history and mycorrhizal symbioses. Evidence of associations between leaf N and root structure, chemical defense and metabolic activity was found across the broad taxonomical range of species. Across broad genera as well as within more closely related plants, plants with high leaf N had greater SRL. Few correlations were found between root traits and SLA or trunk growth rate. However, shoot traits could not be used to predict root traits because, in general, relationships were not strong. Morphological traits compared between fast- and slow-growing species across pairs of related species were usually consistent with the seedling study. Physiological traits compared between fast- and slow-growing species across pairs of related species, however, were not consistent with the seedling study.