AME 64:275-284 (2011)  -  DOI: https://doi.org/10.3354/ame01530

ABSTRACT: Photodissolution converts particulate organic matter to dissolved organic matter, which may affect its availability to heterotrophic organisms. We examined the ability of planktonic microbes to utilize photodissolved organic matter (PDOM) obtained from irradiating coastal sediments and a preparation of algal membranes. About half of the organic carbon that was photodissolved from algal particulate detritus was subsequently available to microbes over 2 wk of incubation in the dark, while that from the sediments appeared to be less bioavailable, the extent of utilization being 16 to 29%. Losses in total organic carbon during microbial incubation appeared as dissolved inorganic carbon, substantiating our inference of microbial usage. Accumulation of bacterial biomass was small relative to respiratory loss, which may be due to low growth efficiency by bacteria, or possibly grazing. Photoammonification converted some of the particulate nitrogen into inorganic ammonium; in the subsequent microbial processing of PDOM from sediments, this ammonium was reincorporated into organic matter. Thus, photodissolution shifts particulate organic matter to physical and chemical forms less available to metazoans and more available to osmotrophic microbes. This bioavailability, on a time scale of weeks, indicates that PDOM produced in nearshore resuspension zones can add fuel to planktonic microbial regeneration processes while the water remains on the shelf, but that major fractions of the PDOM are likely to be exported offshore.

KEY WORDS: Photodissolution · Bioavailability · Bacteria · Dissolved organic matter · Resuspended sediments · Photoammonification