CARBON AND NITROGEN FLUXES DURING DECOMPOSITION OF SPARTINA ALTERNIFLORA IN A FLOW-THROUGH PERCOLATOR

¹ Department of Biochemistry and Microbiology, Cook College, New Jersey Agricultural Experiment Station, Rutgers—The State University of New Jersey, New Brunswick, N. J. 08903

The carbon and nitrogen in Spartina alterniflora litter were monitored for 4 months during decomposition at 20°C in a flow-through percolator that simulates an aerobic, moist marsh. Both the evolution of CO₂ and the loss of carbon from the litter followed exponential decay kinetics (0.5% day^-1 and 1.0% day^-1). At first both total organic carbon and total organic nitrogen 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 about 0.25 mg N.g litter^-1.day^-1 initially, but the rate declined eventually to about 0.08 mg N.g litter^-1.day^-1 after 40 days. Nitrogen enrichment of the litter occurred in two phases with peaks on days 40 and 100. Nitrification started at day 30 and was the main consumer of NH₄. The final litter nitrogen concentration was 60% of the initial.

Microbially produced organic matter, calculated from incorporated NH₄, increased during decomposition to a constant value of 250 mg.g dry weight ^-1 in the system; about 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.