Inorganic Carbon Fixation Rates Research Articles

Significant dark inorganic carbon fixation in the euphotic zone of an oligotrophic sea

AbstractEstimates of primary productivity have traditionally disregarded dark inorganic carbon fixation by marine microorganisms. Currently, only limited data are available from different systems on this potentially ecologically important process. We present monthly dark inorganic carbon fixation and photosynthetic rates from the euphotic layer of the northern Gulf of Aqaba collected over a decade between 2010 and 2020. Averaged dark inorganic carbon fixation rates from surface to 100 m depth, ranged from 99 to 173 mg C m−2 d−1, which corresponds to ~ 43% of the annual primary productivity at this location. The lowest dark inorganic carbon fixation rates were found during winter, contributing ~ 7.5% of the integrated primary productivity. During the oligotrophic summer, dark inorganic carbon fixation comprised a larger fraction of the integrated primary productivity estimated as ~ 12%. In accordance, dark inorganic carbon fixation contributed ~ 6% to the particulate organic carbon flux during the winter and ~ 30% during summertime. Complimentary nutrient‐enrichment bioassays of seawater from 5 m show that dissolved organic nutrient enrichment (P and C based) significantly elevates dark inorganic carbon fixation, whereas addition of dissolved inorganic nutrients (, , or both) significantly increased photosynthesis but to a lesser extent dark inorganic carbon fixation. These results suggest that dark inorganic carbon fixation may be an important biochemical process throughout the euphotic zone of oligotrophic seas, and thus should be incorporated into oceanic carbon production estimates.

High dark inorganic carbon fixation rates by specific microbial groups in the Atlantic off the Galician coast (NW Iberian margin).

Bulk dark dissolved inorganic carbon (DIC) fixation rates were determined and compared to microbial heterotrophic production in subsurface, meso- and bathypelagic Atlantic waters off the Galician coast (NW Iberian margin). DIC fixation rates were slightly higher than heterotrophic production throughout the water column, however, more prominently in the bathypelagic waters. Microautoradiography combined with catalyzed reporter deposition fluorescence in situ hybridization (MICRO-CARD-FISH) allowed us to identify several microbial groups involved in dark DIC uptake. The contribution of SAR406 (Marinimicrobia), SAR324 (Deltaproteobacteria) and Alteromonas (Gammaproteobacteria) to the dark DIC fixation was significantly higher than that of SAR202 (Chloroflexi) and Thaumarchaeota, in agreement with their contribution to microbial abundance. Q-PCR on the gene encoding for the ammonia monooxygenase subunit A (amoA) from the putatively high versus low ammonia concentration ecotypes revealed their depth-stratified distribution pattern. Taken together, our results indicate that chemoautotrophy is widespread among microbes in the dark ocean, particularly in bathypelagic waters. This chemolithoautotrophic biomass production in the dark ocean, depleted in bio-available organic matter, might play a substantial role in sustaining the dark ocean's food web.

Photoregulation in a Kleptochloroplastidic Dinoflagellate, Dinophysis acuta.

Some phagotrophic organisms can retain chloroplasts of their photosynthetic prey as so-called kleptochloroplasts and maintain their function for shorter or longer periods of time. Here we show for the first time that the dinoflagellate Dinophysis acuta takes control over “third-hand” chloroplasts obtained from its ciliate prey Mesodinium spp. that originally ingested the cryptophyte chloroplasts. With its kleptochloroplasts, D. acuta can synthesize photosynthetic as well as photoprotective pigments under long-term starvation in the light. Variable chlorophyll fluorescence measurements showed that the kleptochloroplasts were fully functional during 1 month of prey starvation, while the chlorophyll a-specific inorganic carbon uptake decreased within days of prey starvation under an irradiance of 100 μmol photons m-2 s-1. While D. acuta cells can regulate their pigmentation and function of kleptochloroplasts they apparently lose the ability to maintain high inorganic carbon fixation rates.

Contrasting responses of DMS and DMSP to ocean acidification in Arctic waters

Abstract. Increasing atmospheric CO2 is decreasing ocean pH most rapidly in colder regions such as the Arctic. As a component of the EPOCA (European Project on Ocean Acidification) pelagic mesocosm experiment off Spitzbergen in 2010, we examined the consequences of decreased pH and increased pCO2 on the concentrations of dimethylsulphide (DMS). DMS is an important reactant and contributor to aerosol formation and growth in the Arctic troposphere. In the nine mesocosms with initial pHT 8.3 to 7.5, equivalent to pCO2 of 180 to 1420 μatm, highly significant but inverse responses to acidity (hydrogen ion concentration [H+]) occurred following nutrient addition. Compared to ambient [H+], average concentrations of DMS during the mid-phase of the 30 d experiment, when the influence of altered acidity was unambiguous, were reduced by approximately 60% at the highest [H+] and by 35% at [H+] equivalent to 750 μatm pCO2, as projected for 2100. In contrast, concentrations of dimethylsulphoniopropionate (DMSP), the precursor of DMS, were elevated by approximately 50% at the highest [H+] and by 30% at [H+] corresponding to 750 μatm pCO2. Measurements of the specific rate of synthesis of DMSP by phytoplankton indicate increased production at high [H+], in parallel to rates of inorganic carbon fixation. The elevated DMSP production at high [H+] was largely a consequence of increased dinoflagellate biomass and in particular, the increased abundance of the species Heterocapsa rotundata. We discuss both phytoplankton and bacterial processes that may explain the reduced ratios of DMS:DMSPt (total dimethylsulphoniopropionate) at higher [H+]. The experimental design of eight treatment levels provides comparatively robust empirical relationships of DMS and DMSP concentration, DMSP production and dinoflagellate biomass versus [H+] in Arctic waters.

Dark inorganic carbon fixation sustains the functioning of benthic deep‐sea ecosystems

Previous studies have provided evidence that dark inorganic carbon fixation is an important process for the functioning of the ocean interior. However, its quantitative relevance and ecological significance in benthic deep‐sea ecosystems remain unknown. We investigated the rates of inorganic carbon fixation together with prokaryotic abundance, biomass, assemblage composition, and heterotrophic carbon production in surface sediments of different benthic deep‐sea systems along the Iberian margin (northeastern Atlantic Ocean) and in the Mediterranean Sea. Inorganic carbon fixation rates in these surface deep‐sea sediments did not show clear depth‐related patterns, and, on average, they accounted for 19% of the total heterotrophic biomass production. The incorporation rates of inorganic carbon were significantly related to the abundance of total Archaea (as determined by catalyzed reporter deposition fluorescence in situ hybridization) and completely inhibited using an inhibitor of archaeal metabolism, N1‐guanyl‐1,7‐diaminoheptane. This suggests a major role of the archaeal assemblages in inorganic carbon fixation. We also show that benthic archaeal assemblages contribute approximately 25% of the total 3H‐leucine incorporation. Inorganic carbon fixation in surface deep‐sea sediments appears to be dependent not only upon chemosynthetic processes but also on heterotrophic/mixotrophic metabolism, as suggested by estimates of the chemolithotrophic energy requirements and the enhanced inorganic carbon fixation due to the increase in the availability of organic trophic resources. Overall, our data suggest that archaeal assemblages of surface deep‐sea sediments are responsible for the high rates of inorganic carbon incorporation and thereby sustain the functioning of the food webs as well as influence the carbon cycling of benthic deep‐sea ecosystems.

Invariable biomass‐specific primary production of taxonomically discrete picoeukaryote groups across the Atlantic Ocean

Oceanic photosynthetic picoeukaryotes (< 3 µm) are responsible for > 40% of total primary production at low latitudes such as the North-Eastern tropical Atlantic. In the world ocean, warmed by climate changes, the expected gradual shift towards smaller primary producers could render the role of photosynthetic picoeukaryotes even more important than they are today. Little is still known, however, about how the taxonomic composition of this highly diverse group affects primary production at the basin scale. Here, we combined flow cytometric cell sorting, NaH¹⁴CO₃ radiotracer incubations and class-specific fluorescence in situ hybridization (FISH) probes to determine cell- and biomass-specific inorganic carbon fixation rates and taxonomic composition of two major photosynthetic picoeukaryote groups on a ∼7500-km-long latitudinal transect across the Atlantic Ocean (Atlantic Meridional Transect, AMT19). We show that even though larger cells have, on average, cell-specific CO₂ uptake rates ∼5 times higher than the smaller ones, the average biomass-specific uptake is statistically similar for both groups. On the other hand, even at a high taxonomic level, i.e. class, the contributions to both groups by Prymnesiophyceae, Chrysophyceae and Pelagophyceae are significantly different (P < 0.001 in all cases). We therefore conclude that these group's carbon fixation rates are independent of the taxonomic composition of photosynthetic picoeukaryotes across the Atlantic Ocean. Because the above applies across different oceanic regions the diversity changes seem to be a secondary factor determining primary production.

Genomic signatures of fifth autotrophic carbon assimilation pathway in bathypelagic Crenarchaeota

SummaryMarine Crenarchaeota, ubiquitous and abundant organisms in the oceans worldwide, remain metabolically uncharacterized, largely due to their low cultivability. Identification of candidate genes for bicarbonate fixation pathway in the Cenarchaeum symbiosum A was an initial step in understanding the physiology and ecology of marine Crenarchaeota. Recent cultivation and genome sequencing of obligate chemoautotrophic Nitrosopumilus maritimus SCM1 were a major breakthrough towards understanding of their functioning and provide a valuable model for experimental validation of genomic data. Here we present the identification of multiple key components of 3‐hydroxipropionate/4‐hydroxybutyrate cycle, the fifth pathway in carbon fixation, found in data sets of environmental sequences representing uncultivated superficial and bathypelagic Crenarchaeota from Sargasso sea (GOS data set) and KM3 (Mediterranean Sea) and ALOHA (Atlantic ocean) stations. These organisms are likely to use acetyl‐CoA/propionyl‐CoA carboxylase(s) as CO2‐fixing enzyme(s) to form succinyl‐CoA, from which one molecule of acetyl‐CoA is regenerated via 4‐hydroxybutyrate cleavage and another acetyl‐CoA to be the pathway product. The genetic distinctiveness and matching sympatric abundance imply that marine crenarchaeal genotypes from the three different geographic sites share similar ecophysiological properties, and therefore may represent fundamental units of marine ecosystem functioning. To couple results of sequence comparison with the dark ocean primary production, dissolved inorganic carbon fixation rates were measured at KM3 Station (3000 m depth, Eastern Mediterranean Sea), i.e. at the same site and depth used for metagenomic library construction.