EXPERIMENTAL DEGRADATION OF DETRITUS MADE FROM THE SALT-MARSH PLANTS SPARTINA-ALTERNIFLORA LOISEL, SALICORNIA-VIRGINICA I, AND JUNCUS-ROEMERIANUS SCHEELE

The pattern of decomposition and potential food value of detritus derived from the C4 photosynthetic pathway plant Spartina alterniflora Loisel. and the C3 pathway plants Salicornia virginica L. and Juncus roemerianus Scheele were compared. Detrital particles < 125 μm in size made from standing dead plant material were incubated aerobically and anaerobically in phosphate-enriched estuarine water with and without added ammonium chloride. The most rapid decreases in ash-free dry weight (AFDW) and increases in microbial biomass (estimated by increases in ATP and in particulate nitrogen as % of AFDW) were under aerobic conditions with added nitrogen. Material in the aerobic treatment without added nitrogen degraded only slightly faster than in the anaerobic treatments. The dissolved organic carbon (DOC) in the cultures was < 5% of the total detrital carbon; the DOC content decreased during the first week, most rapidly in the aerobic cultures, and then began to increase slowly. Rates of nitrogen fixation in the cultures were low, and were depressed by the presence of O2 and NH4+, and by a higher nitrogen content of the detritus. Salicornia detritus initially degraded the fastest but showed the lowest conversion efficiency of plant material to microbial biomass (19.4%). Spartina detritus had the highest conversion efficiency (64.3%), while Juncus, which decomposed most slowly, had a conversion efficiency of 55.6%. From 87 to 100% of the increase in nitrogen content of the plant detritus is ascribed to proteinnitrogen. Our results suggest that 1. 1) optimum in situ sites for rapid degradation of plant detritus in estuaries are the sediment-air and sediment-water interfaces; and 2. 2) detritus made from the C4 plant Spartina yields a richer food source for estuarine consumers than detritus made from the C3 plants Salicornia and Juncus. © 1979.