FINE-ROOT GROWTH PHENOLOGY, PRODUCTION, AND TURNOVER IN A NORTHERN HARDWOOD FOREST ECOSYSTEM

A large part of the nutrient flux in deciduous forests is through fine root turnover, yet this process is seldom measured. As part of a nutrient cycling study, fine root dynamics were studied for two years at Huntington Forest in the Adirondack Mountain region of New York, USA. Root growth phenology was characterized using field rhizotrons, three methods were used to estimate fine root production, two methods were used to estimate fine root mortality, and decomposition was estimated using the buried bag technique. During both 1986 and 1987, fine root elongation began in early April, peaked during July and August, and nearly ceased by mid-October. Mean fine root (less than or equal to 3 mm diameter) biomass in the surface 28-cm was 2.5 t ha(-1) and necromass was 2.9 t ha(-1). Annual decomposition rates ranged from 17 to 30% beneath the litter and 27 to 52% at a depth of 10 cm. Depending on the method used for estimation, fine root production ranged from 2.0 to 2.9 t ha(-1), mortality ranged from 1.8 to 3.7 t ha(-1) yr(-1), and decomposition was 0.9 t ha(-1) yr(-1). Thus, turnover ranged from 0.8 to 1.2 yr(-1). The nutrients that cycled through fine roots annually were 4.5-6.1 kg Ca, 1.1-1.4 kg Mg, 0.3-0.4 kg K, 1.2-1.7 kg P, 20.3-27.3 kg N, and 1.8-2.4 kg S ha(-1). Fine root turnover was less important than leaf litterfall in the cycling of Ca and Mg and was similar to leaf litterfall in the amount of N, P, K and S cycled.