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The air–sea exchange and oceanic cycling of greenhouse gases (GHG), including carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4), carbon monoxide (CO), and nitrogen oxides (NOx = NO + NO2), are fundamental in controlling the evolution of the Earth’s atmospheric chemistry and climate. Significant advances have been made over the last 10 years in understanding, instrumentation and methods, as well as deciphering the production and consumption pathways of GHG in the upper ocean (including the surface and subsurface ocean down to approximately 1000 m). The global ocean under current conditions is now well established as a major sink for CO2, a major source for N2O and a minor source for both CH4 and CO. The importance of the ocean as a sink or source of NOx is largely unknown so far. There are still considerable uncertainties about the processes and their major drivers controlling the distributions of N2O, CH4, CO, and NOx in the upper ocean. Without having a fundamental understanding of oceanic GHG production and consumption pathways, our knowledge about the effects of ongoing major oceanic changes—warming, acidification, deoxygenation, and eutrophication—on the oceanic cycling and air–sea exchange of GHG remains rudimentary at best. We suggest that only through a comprehensive, coordinated, and interdisciplinary approach that includes data collection by global observation networks as well as joint process studies can the necessary data be generated to (1) identify the relevant microbial and phytoplankton communities, (2) quantify the rates of ocean GHG production and consumption pathways, (3) comprehend their major drivers, and (4) decipher economic and cultural implications of mitigation solutions.
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Forage conservation is a neglected nitrous oxide source
Abstract Agricultural activities are the major anthropogenic source of nitrous oxide (N2O), an important greenhouse gas and ozone-depleting substance. However, the role of forage conservation as a potential source of N2O has rarely been studied. We investigated N2O production from the simulated silage of the three major crops—maize, alfalfa, and sorghum—used for silage in the United States, which comprises over 90% of the total silage production. Our findings revealed that a substantial N2O could be generated, potentially placing forage conservation as the third largest N2O source in the agricultural sector. Notably, the application of chlorate as an additive significantly reduced N2O production, but neither acetylene nor intermittent exposure to oxygen showed any impact. Overall, the results highlight that denitrifiers, rather than nitrifiers, are responsible for N2O production from silage, which was confirmed by molecular analyses. Our study reveals a previously unexplored source of N2O and provides a crucial mechanistic understanding for effective mitigation strategies.
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- Award ID(s):
- 2144189
- PAR ID:
- 10543879
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- PNAS Nexus
- Volume:
- 3
- Issue:
- 9
- ISSN:
- 2752-6542
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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