Differences in litter quality among fine root orders may lead to variability in root decomposition rates in a Pinus palustris forest

Fine root (<2 mm diameter) decomposition represents a considerable flux of C and nutrients that depends largely on the substrate quality of root litter. However, decomposition studies typically do not account for variation in substrate quality or decay rates within fine root branching networks. To determine if substrate quality depended on branch position within the fine root network, the roots of three species: Astrida stricta, P. palustris, and Quercus laevis were dissected by order . Dissected roots were analyzed for morphology and tissue chemistry parameters with potential to affect decomposition rates, including length, diameter, surface area to volume (SA:V) ratio, concentrations of N, P, Ca, C extractives, cellulose, and lignin, as well as C:N, C:P, lignin:N and lignin:P ratios. For each species, significant differences (P<0.05) in each parameter were found among orders, except for Ca in P. palustris and extractives, cellulose, C:N, and lignin:N in A. stricta, which did not vary significantly across order. From distal to proximal across root orders, length and diameter increased across species, while SA:V ratio decreased. Concentrations of N, P, Ca, and lignin generally decreased across orders, while cellulose, C:N, C:P, lignin:N, and lignin:P ratios generally increased. Extractives did not vary systematically across orders. Patterns of variation in morphology and tissue chemistry traits suggest that the smallest, most distal roots should decompose more quickly. Furthermore, this variation among orders strongly suggests that fine roots can no longer be treated as a homogenous cohort in root decomposition studies.