Decomposition and nutrient dynamics of litter from four species of freshwater emergent macrophytes

Abstract

Nitrogen and phosphorus concentrations and mass remaining were followed for 30 months in decomposing litter of the perennial macrophytes Typha latifolia L., Carex lacustris Willd., Calamagrostis canadensis (Michx.) Nutt., and the annual Zizania aquatica L. in a fresh water tidal marsh in Massachusetts. Step-wise decreases in the mass remaining that corresponded to seasonal temperature changes were observed for all species. A model that assumes that initial litter inputs to the marsh surface consist of refractory and labile fractions and that the decay rate of the labile fraction is an exponential function of inverse temperature produced an acceptable description of the observed litter decomposition. The model suggests that a refractory fraction of 11% of initial litter weight of the annual Zizania and from 18 to 23% in the perennial species persists while labile organics are largely degraded within 1 yr. Zizania litter, which had the highest initial concentrations of both N and P, contained the lowest amounts of N and P after 30 months of decomposition. In the three perennial species studied, which are the dominant macrophytes in this marsh, there was a net accumulation of N and P in litter during the first 5 months of decomposition that was about 36% and 100%, respectively, of the annual N and P losses by vegetation in litterfall. This phase of nutrient accumulation was followed by nutrient release, particularly of N, after plant roots had invaded the litter. This sequence of nutrient accumulation, root invasion, and nutrient release represents a mechanism for nutrient conservation and/or accumulation in this ecosystem.