RELATIONSHIPS AMONG ROOF BRANCH ORDER, CARBON, AND NITROGEN IN 4 TEMPERATE SPECIES

The objective of this study was to examine how root length, diameter, specific root length, and root carbon and nitrogen concentrations were related to root branching patterns. The branching root systems of two temperate tree species, Acer saccharum Marsh. and Fraxinus americana L., and two perennial herbs from horizontal rhizomes, Hydrophyllum can adense L. and Viola pubescens Ait., were quantified by dissecting enti re root systems collected from the understory of an A. saccharum-Fagus grandifolia Ehrh. forest. The root systems of each species grew accor ding to a simple branching process. with laterals emerging from the ma in roots some distance behind the tip. Root systems normally consisted of only 4-6 branches (orders). Root diameter. length, and number of b ranches declined with increasing order and there were significant diff erences among species. Specific root length increased with order in al l species. Nitrogen concentration increased with order in the trees, b ut remained constant in the perennial herbs. More than 75% of the cumu lative root length of tree seedling root systems was accounted for by short (2-10 mm) lateral roots almost always <0.3 mm in diameter. Simpl e assumptions suggest that many tree roots normally considered part of the dynamic fine-root pool all roots < 2.0 mm in diameter) are too la rge to exhibit rapid rates of production and mortality. The smallest t ree roots may be the least expensive to construct but the most expensi ve to maintain based on an increase in N concentration with order.