Jan 31, 2013
Very interesting idea! I wonder what size populations of the organisms would be needed and how their presence would affect oxygen levels during decomposition.
Jan 31, 2013
Good questions! 1) Regarding the size of populations needed: The size of the populations that would be needed would be large- the engineered organisms would have to be released on a large scale to make any difference in N2O concentrations, unless they were concentrated in certain hotspots. Even then, within the hotspots you would need a large number or organisms consuming the N2O. For this reason, it would be important to ensure that the organisms would be competitive compared to the other micro-organisms in the same environment. 2) Regarding the oxygen levels: Oxygen levels would not be affected. The microbial process that consumes N2O (denitrification) does not affect oxygen. Rather it is the other way around- denitrification can only occur at low O2 levels and thus N2O consumption only happens in very limited low oxygen locations. If you could enable the enzyme that consumes N2O to function at just slightly higher oxygen levels, the zone in which N2O could be consumed would be greatly (non-linearly) expanded.
Mar 4, 2013
Thanks for the proposal! You mention denitrification in your comments. This, I think, refers to the fact that in oxygen limited environments certain microorganisms can consume nitrates (compounds with NO3-) instead of free oxygen, and N2O is produced as a byproduct. Now, some microorganisms can also consume N2O (a greenhouse gas), extracting oxygen from these molecules and producing N2 -- and these organisms are critical to your proposal. Is this understanding of mine correct? Are these N2O-consuming organisms, critical to your proposal, different from the organisms that can consume nitrates? That is, are there organisms that prefer the the N2O --> N2 reaction while avoiding the NO3- --> N2O set of reactions? Sorry to possibly make you restate aspects of your proposal, but I think this is an important point that needs clarifying.
Mar 4, 2013
Your question: Are the denitrifying organisms that consume NO3 and produce N2O the same as the ones that consume N2O? Answer: Yes, but my understanding is that whether denitrification leads to net N2O production or consumption in a system depends on whether the denitrifier's enzyme nitrous oxide reductase is enabled (Spiro et al., 2012). In oceans, O2 concentrations appear to determine the activity of nitrous oxide reductase (Zamora et al., 2012). In soils, copper concentrations have a more important role (Thompson et al., 2012). This proposal focuses more on oceans than on soils, although something similar could be done for soils potentially. Also, to clarify, the goal would not be to enable denitrification to occur more. This would be bad, because more denitrification could lead to a great loss of NO3- in the system, and NO3 is an important nutrient. Instead, the goal would be to increase the amount of N2O consumed during denitrification by reducing the sensitivity of nitrous oxide reductase. That way, denitrification would occur in the same places as before, but the O2 concentration at which N2O would be consumed would be raised, leading to more N2O consumption in the locations where denitrification occurs anyway. The byproducts of this switch would be more N2 and less N2O being produced during denitrification. References Spiro et al. (2012), Nitrous oxide production and consumption: regulation of gene expression by gas-sensitive transcription factors, Phil. Trans. R. Soc. B., 367, 1213-1225, doi: 10.1098/rstb.2011.0309 Thompson et al. (2012), Introduction: Biological sources and sinks of nitrous oxide and strategies to mitigate emissions, Phil. Trans. R. Soc. B, 367, 1157-1168, doi: 10.1098/rstb.2011.0415, http://rstb.royalsocietypublishing.org/content/367/1593/1157.full Zamora et al. (2012), Nitrous oxide dynamics in low oxygen regions of the Pacific: insights from the MEMENTO database, Biogeosciences, 9, 5007-5022, doi:10.5194/bg-9-5007-2012, http://www.biogeosciences.net/9/5007/2012/bg-9-5007-2012.html
May 1, 2013
I am a bit confused by the proposal. On the one hand, the proposal says that emissions would be reduced. I thought that much of the N2O emissions came from agriculture (specifically relating to fertilizer use). If this is the case, then the question would seem to be what effect such organisms might have on growth of agriculturally important organisms and crop production, etc.? And if introduced into the soils, how might the organisms spread into and affect natural ecosystems, etc.? On the other hand, I get the impression that the process would take place in the oceans. This presumably means limiting production of N2O in the denitrification process in the ocean. But is the ocean a major source of atmospheric N2O? Would reducing production in the ocean be enough to pull in N2O from the atmosphere, thus reducing the N2O concentration. My understanding is that N2O is not rapidly taken up by the ocean, which is why its lifetime is a few hundred years. So, it is not clear to me how the proposal would significantly reduce the present atmospheric concentration. My apologies if I did not read it all closely enough--and the need for some clarification.
Jul 10, 2013
Thank you for sharing your ideas and for the work invested to create this proposal. We have considered this proposal carefully, and note that clarifications have been requested in comments (where the intervention would occur, what the effects would be on agriculture and ecosystems, how it would reduce present atmospheric concentration of N2O as opposed to future emissions) but have not been addressed. Furthermore, while the list of 5 actions being proposed are good ones, the feasibility of the scheme depends critically on the answers to the questions #1, #2 and #4 that are being asked there. More evidence in favor of the scheme on these issues would have strengthened the case for its feasibility.