Abstract
AbstractBenthic diatoms are important primary producers in intertidal marine sediments and form the basis of the food web in these ecosystems. In order to investigate the carbon flow within diatom mats, we performed in situ 13C pulse‐chase labeling experiments and followed in detail the biochemical fate of carbon fixed by the diatoms for five consecutive days. These labeling experiments were done at approximately 2‐monthly intervals during 1 yr in order to cover seasonal variations. The fixed carbon was recovered in individual carbohydrates including extracellular polymeric substances (EPS), amino acids, fatty acids, and nucleic acid bases. In addition, we assessed a variety of environmental parameters and photosynthetic characteristics. The fixed carbon was initially mainly stored as carbohydrate (glucose) while nitrogen‐rich compounds (e.g., amino acids and RNA/DNA) were produced more slowly. During the year, the diatoms distributed the photosynthetically fixed carbon differently among the various carbon pools that were measured. In summer, the diatoms decreased carbon fixation and accumulated relatively more lipid as a storage compound (27% ± 2% vs. 12% ± 5% in other seasons). The percentage of fixed carbon that was excreted as EPS was lower in summer compared to other seasons, amounting 9% ± 4% and 21% ± 6%, respectively. Hence, it seemed that the physiology of the microphytobenthos was different during summer and caused by higher light intensity and a shift in nitrogen source.
Highlights
Benthic diatoms are important primary producers in intertidal marine sediments and form the basis of the food web in these ecosystems
Under nitrogen deficiency or other adverse environmental conditions, the intermediate metabolism is altered and the fate of fixed carbon is directed to triglycerides, which may serve as a storage compound (Hu et al 2008; Hockin et al 2012)
Seasonal development of the diatom mat Benthic diatoms were visible on the sediment surface during the whole year but varied in density, depending on the time of the year and the time of the day
Summary
Benthic diatoms are important primary producers in intertidal marine sediments and form the basis of the food web in these ecosystems. The percentage of fixed carbon that was excreted as EPS was lower in summer compared to other seasons, amounting 9% 6 4% and 21% 6 6%, respectively It seemed that the physiology of the microphytobenthos was different during summer and caused by higher light intensity and a shift in nitrogen source. Diatoms are the dominant group in microphytobenthic communities and can form dense mats at the sediment surface (Admiraal et al 1984; MacIntyre and Cullen 1996) These mats provide a major source of carbon for the successive trophic levels, including microbes (Herman et al 2000; Middelburg et al 2000; Taylor et al 2013; Como et al 2014). Space for intracellular storage of reserve compounds is obviously limited and excess fixed carbon can be Moerdijk-Poortvliet et al
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