抄録
To test the hypothesis that different phytoplankton cellular components undergo distinct decomposition processes, we examined bacterial decomposition of extracted dissolved organic matter (EX-DOM) and cell debris from the diatom (Skeletonema costatum) using long-term incubation experiments. The decay rates indicated that EX-DOM is extremely bioreactive (1.2-1.7 d-1), and that particulate organic carbon (POC) from cell debris is resistant to rapid microbial degradation (0.047-0.055 d-1). In the experiment with grazers, the percentage of accumulated dissolved organic carbon (DOC) in the EX-DOM and cell debris experiments was 5% and 64%, respectively, of the initial DOC concentrations derived from phytoplankton cells. The initial C/N ratio of DOM in the cell debris experiments was 19.2-19.7, higher than those in the EX-DOM experiments (5.5-6.0). The percentage of accumulated DOC in the cell debris experiment with grazers was 35% at day 13. Thereafter DOC accumulated until it reached 64%. Our data indicate that these two distinct phytoplankton-derived organic materials (EX-DOM and cell debris) decay and accumulate differently. These results suggest that structural components of phytoplankton cells may persist as semi-labile POC, and that DOC produced by solubilization of structural components of cell and phytoplankton-derived DOM with high C/N ratios may accumulate as semi-labile DOC in seawater.
