Comment on “The complex effects of ocean acidification on the prominent N
            <sub>2</sub>
            -fixing cyanobacterium
            <i>Trichodesmium</i>
            ”

Hutchins, David A.; Fu, Fei-Xue; Walworth, Nathan G.; Lee, Michael D.; Saito, Mak A.; Webb, Eric A.

doi:10.1126/science.aao0067

Cited by 13 publications

(5 citation statements)

References 15 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In a recent study, Hong et al (9) observed a significant decrease in growth and N 2 fixation rates under both replete (r750) and Fe-limited conditions at high CO 2 concentrations (750-Fe) relative to the controls, unlike this study and a number of other previous replete (3-6, 10, 25-28) and high-CO 2 /Fe-limited studies (5). Hong et al (9) attributed these discrepancies to ammonia contamination and metal toxicity in all other past studies, although ammonia was below the detection limit in our prepared Aquil medium and 25 M EDTA was added to control for metal toxicity (29). One central difference between this study and nearly all others relative to that of Hong et al (9) is that Trichodesmium cell lines were adapted (4-6) or acclimated (10,(26)(27)(28) to a low pH as a product of increasing CO 2 partial pressure on seawater carbonate chemistry similar to pH reductions in situ.…”

Section: Resultsmentioning

confidence: 74%

Nutrient-Colimited Trichodesmium as a Nitrogen Source or Sink in a Future Ocean

Walworth

Lee

et al. 2018

Appl Environ Microbiol

Self Cite

View full text Add to dashboard Cite

Nitrogen-fixing (N) cyanobacteria provide bioavailable nitrogen to vast ocean regions but are in turn limited by iron (Fe) and/or phosphorus (P), which may force them to employ alternative nitrogen acquisition strategies. The adaptive responses of nitrogen-fixers to global-change drivers under nutrient-limited conditions could profoundly alter the current ocean nitrogen and carbon cycles. Here, we show that the globally-important N-fixer fundamentally shifts nitrogen metabolism towards organic-nitrogen scavenging following long-term high-CO adaptation under iron and/or phosphorus (co)-limitation. Global shifts in transcripts and proteins under high CO/Fe-limited and/or P-limited conditions include decreases in the N-fixing nitrogenase enzyme, coupled with major increases in enzymes that oxidize trimethylamine (TMA). TMA is an abundant, biogeochemically-important organic nitrogen compound that supports rapid growth while inhibiting N fixation. In a future high-CO ocean, this whole-cell energetic reallocation towards organic nitrogen scavenging and away from N-fixation may reduce new-nitrogen inputs by , while simultaneously depleting the scarce fixed-nitrogen supplies of nitrogen-limited open ocean ecosystems. is among the most biogeochemically-significant microorganisms in the ocean, since it supplies up to 50% of the new nitrogen supporting open ocean food webs. We used cultures adapted to high CO for 7 years followed by additional exposure to iron and/or phosphorus (co)-limitation. We show that 'future ocean' conditions of high CO and concurrent nutrient limitation(s) fundamentally shift nitrogen metabolism away from nitrogen fixation, and instead towards upregulation of organic-nitrogen scavenging pathways. We show that responses to projected future ocean conditions include decreases in the nitrogen-fixing nitrogenase enzymes, coupled with major increases in enzymes that oxidize the abundant organic nitrogen source trimethylamine (TMA). Such a shift towards organic nitrogen uptake and away from nitrogen fixation may substantially reduce new-nitrogen inputs by to the rest of the microbial community in the future high-CO ocean, with potential global implications for ocean carbon and nitrogen cycling.

show abstract

Section: Resultsmentioning

confidence: 74%

Nutrient-Colimited Trichodesmium as a Nitrogen Source or Sink in a Future Ocean

Walworth

Lee

et al. 2018

Appl Environ Microbiol

Self Cite

View full text Add to dashboard Cite

show abstract

“…So our study reveals that coral species that highly depend on heterotrophy could, in the event of bleaching, rely not only on the supply of nutrients and energy from meso-macroplankton but also on a major supply of N by planktonic diazotrophs and picoplankton. Taking advantage of the consumption of planktonic diazotrophs or picoplankton that have developed on diazotrophy could be one of the main strategies for coral recovery facing bleaching, as both the activity and geographical distribution of diazotrophs will likely increase with future rising sea surface temperature (Breitbarth et al, 2007;Levitan et al, 2007;Hutchins et al, 2017).…”

Section: Discussionmentioning

confidence: 99%

Diazotroph-Derived Nitrogen Assimilation Strategies Differ by Scleractinian Coral Species

et al. 2021

View full text Add to dashboard Cite

Reef-building corals generally thrive in nutrient-poor tropical waters, where among other elements, nitrogen (N) availability often limits primary productivity. In addition to their close association with endosymbiotic dinoflagellates of the family Symbiodiniaceae, enabling an effective use and retention of dissolved inorganic nitrogen (DIN), scleractinian corals have developed strategies to acquire new N: (1) They can ingest N-rich sediment particles and preys (from picoplankton to macro-zooplankton) via heterotrophy, including diazotrophs [plankton fixing dinitrogen (N2) and releasing part of this nitrogen—Diazotroph-Derived N (DDN)—in seawater], a pathway called “heterotrophic nutrition on diazotrophs”; (2) Symbiotic diazotrophs located in the coral holobiont have the molecular machinery to fix N2, a pathway called “symbiotic N2 fixation”. Here we used the 15N2 isotopic labeling in a series of incubations to investigate the relative contribution of each of these DDN transfer pathways in three worldwide distributed coral species: Acropora muricata, Galaxea fascicularis, and Pocillopora damicornis. We show that N provision via “symbiotic N2 fixation” is negligible compared to that obtained via “heterotrophic nutrition on diazotrophs,” with DDN assimilation rates about a thousand times lower for P. damicornis and G. fascicularis, or assimilation rates via “symbiotic N2 fixation” almost nil for A. muricata. Through heterotrophic feeding on planktonic diazotrophs, only G. fascicularis and P. damicornis can successfully obtain N and fulfill a large part of their N requirements (DDN asimilation rates: 0.111 ± 0.056 and 0.517 ± 0.070 μg N cm–2 h–1 in their Symbiodiniaceae, respectively). Whereas this contribution is again negligible for A. muricata. They also largely consume the picoplankton that likely benefit from this DDN (Prochlorococcus and Synechococcus cells; respectively, 2.56 ± 1.57 104 and 2.70 ± 1.66 104 cell h–1 cm–2 for G. fascicularis; 3.02 ± 0.19 105 and 1.14 ± 0.79 104 cell h–1 cm–2 for P. damicornis). The present study confirms the different dependencies of the three tested species regarding heterotrophy, with P. damicornis and G. fascicularis appearing highly efficient at capturing plankton, while A. muricata, considered as mainly autotroph, does not rely on these food resources to meet its N and energy needs.

show abstract

“…Finally, an increase in sea surface stratification linked to sea surface warming, which tends to slow the nutrient supply to the surface, is projected for future oceans (Gattuso et al., ; Roy et al., ). Under these conditions, unpalatable N 2 ‐fixing Trichodesmium are especially favored, and their large blooms are expected to further expand under future global warming scenarios because enhanced N 2 fixation was found to persist under high CO 2 irrespective of phosphorus limitation (Hutchins & Fu, ; Hutchins et al., ; Walworth et al., ). Analogously to Nodularia blooms in the Baltic Sea (Wasmund, Nausch, & Voss, ), blooms of Trichodesmium in other marine systems develop seasonally in association with mixing of DIN‐depleted but phosphorus‐rich upwelling waters into warm, stratified oceanic waters that contain seed populations of Trichodesmium (Deutsch, Sarmiento, Sigman, Gruber, & Dunne, ; Hegde et al., ; Hood, Coles, & Capone, ).…”

Section: Discussionmentioning

confidence: 99%

Stratification, nitrogen fixation, and cyanobacterial bloom stage regulate the planktonic food web structure

Loick‐Wilde

Fernández‐Urruzola

Eglite

et al. 2019

Global Change Biology

View full text Add to dashboard Cite

Changes in the complexity of planktonic food webs may be expected in future aquatic systems due to increases in sea surface temperature and an enhanced stratification of the water column. Under these conditions, the growth of unpalatable, filamentous, N2‐fixing cyanobacterial blooms, and their effect on planktonic food webs will become increasingly important. The planktonic food web structure in aquatic ecosystems at times of filamentous cyanobacterial blooms is currently unresolved, with discordant lines of evidence suggesting that herbivores dominate the mesozooplankton or that mesozooplankton organisms are mainly carnivorous. Here, we use a set of proxies derived from amino acid nitrogen stable isotopes from two mesozooplankton size fractions to identify changes in the nitrogen source and the planktonic food web structure across different microplankton communities. A transition from herbivory to carnivory in mesozooplankton between more eutrophic, near‐coastal sites and more oligotrophic, offshore sites was accompanied by an increasing diversity of microplankton communities with aging filamentous cyanobacterial blooms. Our analyses of 124 biotic and abiotic variables using multivariate statistics confirmed salinity as a major driver for the biomass distribution of non‐N2‐fixing microplankton species such as dinoflagellates. However, we provide strong evidence that stratification, N2 fixation, and the stage of the cyanobacterial blooms regulated much of the microplankton diversity and the mean trophic position and size of the metabolic nitrogen pool in mesozooplankton. Our empirical, macroscale data set consistently unifies contrasting results of the dominant feeding mode in mesozooplankton during blooms of unpalatable, filamentous, N2‐fixing cyanobacteria by identifying the at times important role of heterotrophic microbial food webs. Thus, carnivory, rather than herbivory, dominates in mesozooplankton during aging and decaying cyanobacterial blooms with hitherto uncharacterized consequences for the biogeochemical functions of mesozooplankton.

show abstract

Comment on “The complex effects of ocean acidification on the prominent N ₂ -fixing cyanobacterium Trichodesmium ”

Cited by 13 publications

References 15 publications

Nutrient-Colimited Trichodesmium as a Nitrogen Source or Sink in a Future Ocean

Nutrient-Colimited Trichodesmium as a Nitrogen Source or Sink in a Future Ocean

Diazotroph-Derived Nitrogen Assimilation Strategies Differ by Scleractinian Coral Species

Stratification, nitrogen fixation, and cyanobacterial bloom stage regulate the planktonic food web structure

Contact Info

Product

Resources

About

Comment on “The complex effects of ocean acidification on the prominent N 2 -fixing cyanobacterium Trichodesmium ”

Cited by 13 publications

References 15 publications

Nutrient-Colimited Trichodesmium as a Nitrogen Source or Sink in a Future Ocean

Nutrient-Colimited Trichodesmium as a Nitrogen Source or Sink in a Future Ocean

Diazotroph-Derived Nitrogen Assimilation Strategies Differ by Scleractinian Coral Species

Stratification, nitrogen fixation, and cyanobacterial bloom stage regulate the planktonic food web structure

Contact Info

Product

Resources

About

Comment on “The complex effects of ocean acidification on the prominent N ₂ -fixing cyanobacterium Trichodesmium ”