Production of chromophoric dissolved organic matter by marine phytoplankton

Abstract

Incubation experiments with axenic cultures of four common phytoplankton species of the genera Chaetoceros, Skeletonema, Prorocentrum, and Micromonas were performed to test for the production of fluorescent dissolved organic matter (FDOM) by marine phytoplankton. Our results prove that the four species exuded both fluorescent protein-like and marine humic-like materials in variable amounts, with more production by the diatoms Chaetoceros sp. and Skeletonema costatum and less by Prorocentrum minimum. Whereas the exudation of protein-like substances by healthy phytoplankton cells has been recognized, the in situ production of marine humic-like substances is still a matter of debate. Using axenic cultures, we demonstrate unequivocally that phytoplankton can directly contribute to the autochthonous production of colored humic-like substances in the ocean. Extrapolation of these findings to the field indicates that about 20% of the marine humic-like substances produced in the highly productive coastal upwelling system of the Ría de Vigo could originate from growing phytoplankton. Therefore, the exudation of FDOM by marine phytoplankton should be considered in future studies of the dynamics of colored DOM in marine systems.

Production and Reutilization of Fluorescent Dissolved Organic Matter by a Marine Bacterial Strain, Alteromonas macleodii

“…The combined fluorescence characteristics of H1 and H3 were similar to that found in the most abundant component in the humic acid fraction extracted from sediments/soils (He et al, 2006; Santín et al, 2009). The other humic-like fluorophore (H2: Ex/Em = 315/400 nm), which had a shorter emission wavelength than H1 and H3, was similar to traditionally defined marine/microbial humic-like FDOM (Coble, 1996, 2007) and was also similar to a fluorophore excreted by cultured phytoplankton (Romera-Castillo et al, 2010). …”

“…Fluorescent components similar to H2 were obtained through parallel factor analysis (PARAFAC) of FDOM from the open ocean and were found to be related to apparent oxygen utilization in the deep ocean (Jørgensen et al, 2011; Tanaka et al, 2014), implying that H2 produced by A. macleodii is possibly recalcitrant DOM. On the other hand, peak M was produced by phytoplankton isolates (Romera-Castillo et al, 2010) and consumed partially by bacterial communities (Romera-Castillo et al, 2011). These results suggest that the reactivity of the peak M-type fluorophore was dependent on its source; specifically, the fluorophore produced by heterotrophic bacteria is possibly recalcitrant, while that produced by phytoplankton includes a labile fraction.…”

Shifts in phytoplankton community structure modify bacterial production, abundance and community composition

“…Some diatoms release large proportions (> 20%) of fixed carbon as dissolved organic carbon (DOC), but this is highly species-specific (Wetz & Wheeler 2007). Some dinoflagellates show higher percentages of extra cellular release than dia toms (Castillo et al 2010, López-Sandoval et al 2013. However, during the spring bloom in the Baltic Sea, diatom-dominated communities excrete more DOC than mixed or dinoflagellate-dominated communities (Spilling et al 2014).…”

Stoichiometry, polarity, and organometallics in solid-phase extracted dissolved organic matter of the Elbe-Weser estuary

“…Different sources and sinks control the amount, composition and reactivity of DOM in aquatic environments: biological release, phyto and zooplankton mediated processes [67], decomposition of riverine DOM by marine bacteria [68], photo-bleaching and photo-degradation [69–72] as well as flocculation processes and sorption to sediments [47, 48, 73]. All of these processes might occur simultaneously, and it remains a major challenge to quantify the influence of each process on DOM composition.…”