Nutrient Release From Decomposing Leaf and Branch Litter in the Hubbard Brook Forest, New Hampshire

Abstract

Rates of weight loss and nutrient release (N, P, S, K, Mn, Ca, Zn, Fe, Mn, Cu, Na) were measured in decomposing leaf and branch tissue form yellow birch, sugar maple, and beech, and in branch tissue from red spruce and balsam fir. Neither leaf nor branch decomposition differed significantly over an elevational range of 220 m. Decomposition rates for leaves varied with yellow birch > sugar maple > beech. The decomposition rate for hardwood branches was greater than that for conifer branches, but differences between hardwoods were not significant. Maximum decomposition rates occurred during the summer for both branch and leaf tissue. The rate of nutrient release from decomposing branch and leaf litter appears to be correlated with nutrient concentration in current litter fall, precipitation, and leaf wash. The concentration and absolute weight of N. S. and P in the leaf litter of all species increased with time. The amount of the increase as well as the initiation of nutrient release was influenced by C: element ratios in the leaf tissue. These studies also indicate that P levels can influence the mineralization or immobilization of other important nutrients. Carbon—to—element ratios in decomposing litter varied between species and elevation at different times of the year, but element: P ratios were much more uniform. In branch tissue the physical loss of N— and P—rich bark and buds offset any increase in concentration that would have occurred through decomposition. Potassium and magnesium were rapidly released from the litter by leaching. Similar minimum concentrations in leaf tissue indicate that critical C: element ratios also exist for these elements. Calcium release was similar to dry weight loss, indicating that it is a structural component primarily released by decomposition. Maximum nutrient release from current litter occurred in the autumn and summer. It was not correlated with the nutrient output from the ecosystem which occurred primarily during the spring. The net output of Ca, Mg, and K from the watershed was very small compared to quantities released from current litter. Factors which contribute to the complex nature of decomposition are: seasonal heterotroph activity, heterotroph nutrient demand, environmental conditions regulations heterotroph activity, species tissue palatability, species composition of litter, tissue composition of litter, nutrient content of litter, nutrient mobility, and nutrient input (i.e., leafwash, litter fall).