琵琶湖に棲息する緑藻 Staurastrum arctiscon（Desmidiaceae）の生分解特性に関する研究

The b iodegradability of the green alga Staurastrum arctiscon was studied , using a natural bacterial community sampl ed from Lake Biwa , to understand the genera tion characteristics of dissolved organic carbon (DOC) from the cytoplasm and extracellular polysaccharides (EPS). The biodegradation test revealed that 31% of the particulate organic carbon (POC) of the cytoplasm remained after 200 days of biodegradation and 2−4% of the initial cytoplasm POC was transformed into DOC. Moreover, it was clearly shown that 29−35% of the initial POC of the EPS was transformed into DOC and stably remained after 77 days of biodegradation. The morphology changes of S. arctiscon ob served in the biodegradation experiment s by staining EPS with fl uorescently labeled wheat germ agglutinin (WGA) revealed that the fl uorescen ce intensity gradually decreased over time and disappeared after 21 days of biodegradation, implying the partial deg radation of the EPS. However, the EPS were still present even at 100 days, suggesting that some of the m we re comparatively recalcitrant to biodegradation. Consequently, our results suggest that phytoplankton-derived organic matter may play an important r ole as a source of D OC a nd POC in Lake Biwa.