Stepwise alteration from fluorescent to non-fluorescent chlorophyll derivatives during early diagenesis of phytoplankton in aquatic environments

The alteration of chlorophyll has been elucidated to some extent, particularly in relation to time course and non-fluorescent chlorophyll derivatives (NCDs). The present study attempts to clarify the pathway from chlorophyll to fluorescent chlorophyll derivatives and to NCDs by using high-performance liquid chromatography (HPLC) with fluorescence detection and gas chromatography-mass spectrometry (GC-MS) combined with chromic acid oxidation. Seawater containing microbial populations was incubated under sunlight with nutrients. Next, microbial degradation was allowed to process in the dark for 92 days. Particulate organic matter (POM) samples collected onto glass fiber filters during incubation were analyzed for chlorophyll derivatives. HPLC results suggested that the dominant factors in chlorophyll alteration are the physiological condition of phytoplankton within a few days, and bacterial degradation after a week in the dark. The following sequence is suggested as the main pathway: chlorophyll a, chlorophyllide a, pheophorbide a, and pyropheophorbide a. NCDs were found even at an early stage, and, accounted for most of the derivatives after a month, when the fluorescent derivatives had nearly disappeared. This result implies that a proportion of the chlorophyll remained as NCDs, suggesting a greater contribution of chlorophyll derivatives to POM than that reported in previous studies.