Fine root production and turnover in a northern hardwood forest and the influence of nitrogen availability.

摘要

There were two components to this study. First, the fine root ({dollar}leq{dollar}3 mm in diameter) dynamics in a northern hardwood forest were quantified in a two-year field study. The periodicity of root growth was measured for two calendar years using rhizotrons (root observation boxes). Production and mortality were estimated by the sequential coring method, and decomposition was measured using buried litter bags. There was a five-month period of annual fine root production. The initiation of fine root growth occurred in mid-April, a peak in growth occurred during July and August, and growth cessation occurred in October. Fine root growth periodicity appears to be governed largely by temperature in this forest. A large proportion of fine root biomass turned over annually (70%), with fine root longevity estimated at 1.4 years. Production was estimated at 1.8 to 2.0 t ha{dollar}sp{lcub}-1{rcub}{dollar} yr{dollar}sp{lcub}-1{rcub}{dollar}, mortality was 1.8 to 1.9 t ha{dollar}sp{lcub}-1{rcub}{dollar} yr{dollar}sp{lcub}-1{rcub}{dollar}, decomposition was 0.7 to 1.5 t ha{dollar}sp{lcub}-1{rcub}{dollar} yr{dollar}sp{lcub}-1{rcub}{dollar}, and turnover was 1.5 to 1.8 t ha{dollar}sp{lcub}-1{rcub}{dollar} yr{dollar}sp{lcub}-1{rcub}{dollar}. The fine root biomass appears to be in steady state, evidenced by the similar production, mortality and turnover values. The contribution of fine roots to the detrital pool is estimated as 37% of total detrital input.; The second component of this study was to experimentally determine the influence of soil nitrogen availability on fine root production and carbon allocation patterns in sugar maple (Acer saccharum Marsh.) seedlings. Soil nitrogen availability is correlated with increased yield of foliage, stem, coarse and fine roots, the shoot to root ratios, the increment in root crown diameter and leaf area. In addition, soil nitrogen availability was positively correlated with carbohydrate concentrations in new shoots and negatively correlated with fine root carbohydrate concentrations. This supports the hypothesis that the smaller fine root biomass associated with fertile conditions is not the result of reduced fine root production. Instead, fertile conditions may increase the production and turnover of fine roots, and this is likely the result of different reserve carbohydrate allocation patterns in trees in different nutrient regimes.