Temporal Variability of Dark Carbon Fixation and Bacterial Production and Their Relation with Environmental Factors in a Tropical Estuarine System

Bacterial production prevails over photo- and chemosynthesis in a eutrophic tropical lagoon

“…HBP rates were one to two orders of magnitude higher than DCF, ranging from 25.3 µgC.L -1 .h -1 at the bottom of station 3 to 160.6 µgC.L -1 .h -1 at the surface of station 4 (Figure 2). HBP rates varied over a larger range than DCF across the estuary, both horizontally and vertically, as previously observed in a tropical estuarine system (Signori et al, 2017). However, the microbial production rates did not correlate with depth (r = -0.13 and p = 0.66 for DCF, r = -0.26 and p=0.39 for HBP).…”

“…However, the observed ratios were much lower and less variable than those observed in sediments of tropical and temperate lakes (Santoro et al, 2013) and in the water column of a tropical bay (Signori et al, 2017).…”

“…Water samples (150 mL) were dispensed into transparent polystyrene flasks for photosynthesis and dark flasks covered with silver tape for chemosynthesis and inoculated with 10 μCi of NaH 14 CO 3 solution (specific activity 42.9 mCi mmol -1 , DHI Water & Environment, Denmark). Incubations were performed in situ over 4 h, simulating 100% of incident light (transparent bottle) for photosynthesis, and no light (dark bottle) for DCF, along with one formaldehyde-fixed blank (Steemann-Nielsen, 1952;Herndl et al, 2005;Casamayor et al, 2008;Reinthaler et al, 2010;Signori et al, 2017). After incubations, the samples were pre-filtered onto 0.7-µm GF/F glass microfiber filter (Whatman GE Healthcare, USA) prior to filtering onto 0.2-µm cellulose acetate filters (Sartorius Stedim Biotech, USA) to avoid clogging and losses of biomass, using a Sartorius filtration kit and vacuum pump.…”

“…Camacho et al, 2001 andCasamayor et al, 2010Casamayor et al, , 2012Noguerola et al, 2015). In tropical systems, DCF accounted for an estimated <5% to 89% of the heterotrophic bacterial production in a polluted tropical estuary (Signori et al, 2017), and reached up to 80% in sediments of tropical lakes (Santoro et al, 2013).…”

Reviews and syntheses: Heterotrophic fixation of inorganic carbon – significant but invisible flux in environmental carbon cycling

“…Dark DIC fixation has been reported for all types of ecosystems, including marine habitats (Wuchter et al, 2003;Middelburg, 2011;DeLorenzo et al, 2012;Molari et al, 2013;Lengger et al, 2019;Smith et al, 2019;Vasquez-Cardenas et al, 2020), brackish and freshwater systems (Bräuer et al, 2013;Santoro et al, 2013;Noguerola et al, 2015;Signori et al, 2017;Vick-Majors and Priscu, 2019;Zhao et al, 2020), cave waters and groundwater ecosystems (Pedersen and Ekendahl, 1992a, b;Kotelnikova and Pedersen, 1998;Kellermann et al, 2012;Lazar et al, 2017), and soil habitats (Ehleringer et al, 2000;Miltner et al, 2004Miltner et al, , 2005Šantrůčková et al, 2005Akinyede et al, 2020, and references therein). In the absence of solar radiation, particularly in the dark ocean, CO 2 fixation rates of up to ∼ 125 mg C m −3 d −1 have been measured, amounting to 30 % (on a per volume basis) of the phototrophic CO 2 fixation in ocean surface waters (Zopfi et al, 2001;Detmer et al, 1993;Casamayor et al, 2001;Baltar et al, 2010).…”