Formation and Release of Nitrous Oxide from Terrestrial and Aquatic Ecosystems

Algal photosynthesis converts nitric oxide into nitrous oxide

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1915276117 ◽

2020 ◽

Vol 117 (5) ◽

pp. 2704-2709 ◽

Cited By ~ 6

Author(s):

Adrien Burlacot ◽

Pierre Richaud ◽

Arthur Gosset ◽

Yonghua Li-Beisson ◽

Gilles Peltier

Keyword(s):

Nitrous Oxide ◽

Greenhouse Gas ◽

Aquatic Ecosystems ◽

No Reduction ◽

Greenhouse Gas Emission ◽

Photosynthetic Electron Transport ◽

Photosynthetic Organisms ◽

Green Microalga ◽

Algal Photosynthesis

Nitrous oxide (N2O), a potent greenhouse gas in the atmosphere, is produced mostly from aquatic ecosystems, to which algae substantially contribute. However, mechanisms of N2O production by photosynthetic organisms are poorly described. Here we show that the green microalga Chlamydomonas reinhardtii reduces NO into N2O using the photosynthetic electron transport. Through the study of C. reinhardtii mutants deficient in flavodiiron proteins (FLVs) or in a cytochrome p450 (CYP55), we show that FLVs contribute to NO reduction in the light, while CYP55 operates in the dark. Both pathways are active when NO is produced in vivo during the reduction of nitrites and participate in NO homeostasis. Furthermore, NO reduction by both pathways is restricted to chlorophytes, organisms particularly abundant in ocean N2O-producing hot spots. Our results provide a mechanistic understanding of N2O production in eukaryotic phototrophs and represent an important step toward a comprehensive assessment of greenhouse gas emission by aquatic ecosystems.

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Stimulation of microbial nitrogen cycling in aquatic ecosystems by benthic macrofauna: mechanisms and environmental implications

Biogeosciences Discussions ◽

10.5194/bgd-10-11785-2013 ◽

2013 ◽

Vol 10 (7) ◽

pp. 11785-11824 ◽

Cited By ~ 3

Author(s):

P. Stief

Keyword(s):

Nitrous Oxide ◽

Nitrogen Cycling ◽

Nitrogen Removal ◽

Aquatic Ecosystems ◽

Ecosystem Engineering ◽

Benthic Macrofauna ◽

Published Data ◽

Fixed Nitrogen ◽

Environmental Implications ◽

Microbe Interactions

Abstract. Invertebrate animals that live at the bottom of aquatic ecosystems (i.e., benthic macrofauna) are important mediators between nutrients in the water column and microbes in the benthos. The presence of benthic macrofauna stimulates microbial nutrient dynamics through different types of animal–microbe interactions, which potentially affect the trophic status of aquatic ecosystems. This review contrasts three types of animal–microbe interactions in the benthos of aquatic ecosystems: (i) ecosystem engineering, (ii) grazing, and (iii) symbiosis. Their specific contributions to the turnover of fixed nitrogen (mainly nitrate and ammonium) and the emission of the greenhouse gas nitrous oxide are evaluated. Published data indicate that ecosystem engineering by sediment-burrowing macrofauna stimulates benthic nitrification and denitrification, which together allows fixed nitrogen removal. However, the release of ammonium from sediments often is enhanced even more than the sedimentary uptake of nitrate. Ecosystem engineering by reef-building macrofauna increases nitrogen retention and ammonium concentrations in shallow aquatic ecosystems, but allows organic nitrogen removal through harvesting. Grazing by macrofauna on benthic microbes apparently has small or neutral effects on nitrogen cycling. Animal-microbe symbioses provide abundant and distinct benthic compartments for a multitude of nitrogen-cycle pathways. Recent studies revealed that ecosystem engineering, grazing, and symbioses of benthic macrofauna significantly enhance nitrous oxide emission from shallow aquatic ecosystems. The beneficial effect of benthic macrofauna on fixed nitrogen removal through coupled nitrification–denitrification can thus be offset by the concurrent release of (i) ammonium that stimulates aquatic primary production and (ii) nitrous oxide that contributes to global warming. Overall, benthic macrofauna intensifies the coupling between benthos, pelagial, and atmosphere through enhanced turnover and transport of nitrogen.

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Algal photosynthesis converts nitric oxide into nitrous oxide

10.1101/745463 ◽

2019 ◽

Author(s):

Adrien Burlacot ◽

Pierre Richaud ◽

Arthur Gosset ◽

Yonghua Li-Beisson ◽

Gilles Peltier

Keyword(s):

Nitrous Oxide ◽

Cytochrome P450 ◽

Greenhouse Gas ◽

Aquatic Ecosystems ◽

No Reduction ◽

Greenhouse Gas Emission ◽

Photosynthetic Electron Transport ◽

Photosynthetic Organisms ◽

Green Microalga ◽

Algal Photosynthesis

AbstractNitrous oxide (N2O), a potent greenhouse gas in the atmosphere, is produced mostly from aquatic ecosystems, to which algae substantially contribute. However, mechanisms of N2O production by photosynthetic organisms are poorly described. Here, we show that the green microalga Chlamydomonas reinhardtii reduces NO into N2O using the photosynthetic electron transport. Through the study of C. reinhardtii mutants deficient in flavodiiron proteins (FLVs) or in a cytochrome p450 (CYP55), we show that FLVs contribute to NO reduction in the light, while CYP55 operates in the dark. Furthermore, NO reduction by both pathways is restricted to Chlorophytes, organisms particularly abundant in ocean N2O-producing hotspots. Our results provide a mechanistic understanding of N2O production in eukaryotic phototrophs and represent an important step toward a comprehensive assessment of greenhouse gas emission by aquatic ecosystems.One sentence summaryGreen microalgae produce N2O using flavodiiron proteins in the light and a cytochrome P450 NO reductase in the dark.

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Stimulation of microbial nitrogen cycling in aquatic ecosystems by benthic macrofauna: mechanisms and environmental implications

Biogeosciences ◽

10.5194/bg-10-7829-2013 ◽

2013 ◽

Vol 10 (12) ◽

pp. 7829-7846 ◽

Cited By ~ 75

Author(s):

P. Stief

Keyword(s):

Nitrous Oxide ◽

Nitrogen Cycling ◽

Nitrogen Removal ◽

Aquatic Ecosystems ◽

Ecosystem Engineering ◽

Benthic Macrofauna ◽

Published Data ◽

Fixed Nitrogen ◽

Environmental Implications ◽

Microbe Interactions

Abstract. Invertebrate animals that live at the bottom of aquatic ecosystems (i.e., benthic macrofauna) are important mediators between nutrients in the water column and microbes in the benthos. The presence of benthic macrofauna stimulates microbial nutrient dynamics through different types of animal–microbe interactions, which potentially affect the trophic status of aquatic ecosystems. This review contrasts three types of animal–microbe interactions in the benthos of aquatic ecosystems: (i) ecosystem engineering, (ii) grazing, and (iii) symbiosis. Their specific contributions to the turnover of fixed nitrogen (mainly nitrate and ammonium) and the emission of the greenhouse gas nitrous oxide are evaluated. Published data indicate that ecosystem engineering by sediment-burrowing macrofauna stimulates benthic nitrification and denitrification, which together allows fixed nitrogen removal. However, the release of ammonium from sediments is enhanced more strongly than the sedimentary uptake of nitrate. Ecosystem engineering by reef-building macrofauna increases nitrogen retention and ammonium concentrations in shallow aquatic ecosystems, but allows organic nitrogen removal through harvesting. Grazing by macrofauna on benthic microbes apparently has small or neutral effects on nitrogen cycling. Animal–microbe symbioses provide abundant and distinct benthic compartments for a multitude of nitrogen-cycle pathways. Recent studies reveal that ecosystem engineering, grazing, and symbioses of benthic macrofauna significantly enhance nitrous oxide emission from shallow aquatic ecosystems. The beneficial effect of benthic macrofauna on fixed nitrogen removal through coupled nitrification–denitrification can thus be offset by the concurrent release of (i) ammonium that stimulates aquatic primary production and (ii) nitrous oxide that contributes to global warming. Overall, benthic macrofauna intensifies the coupling between benthos, pelagial, and atmosphere through enhanced turnover and transport of nitrogen.

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