CARBON AND NITROGEN FLUXES DURING DECOMPOSITION OFSPARTINA ALTERNIFLORAIN A FLOW-THROUGH PERCOLATOR

Abstract

The C and N in S. alterniflora litter were monitored for 6 mo. during decomposition at 20.degree. C in a flow-through percolator that simulates an aerobic, moist marsh. The evolution of CO2 and the loss of C from the litter followed exponential decay kinetics (0.5% day-1 and 1.0% day-1). At first both total organic C and total organic N were lost primarily in dissolved form at high rates, but this leaching ceased rapidly. The NH4 added to the inflow was incorporated into the litter at .apprx. 0.25 mg N .cntdot. g litter-1 .cntdot. day-1 initially, but the rate declined eventually to .apprx. 0.08 mg N .cntdot. g litter-1 .cntdot. day-1 after 40 days. N enrichment of the litter occurred in 2 phases with peaks on days 40 and 100. Nitrification started at day 30 and was the main consumer of NH4. The final litter N concentration was 60% of the initial. Microbially produced organic matter, calculated from incorporated NH4, increased during decomposition to a constant value of 250 mg .cntdot. g dry weight-1 in the system; .apprx. 25% of the total dry weight of the litter. The efficiency of conversion of Spartina biomass to microbial organic matter was also biphasic and had maxima of 50% at the start and 70% at day 80 with an intermediate value of 20%. The continuous recovery of organic matter and CO2 exported from the percolator allowed the microbial activity to be separated into different periods dominated by bacteria in the first 40 days and then by fungi for the remaining 80 days.