Oxygen levels in the air do not limit plant productivity

Feb 17, 2011

There have been concerns that present oxygen levels may limit plant productivity. Swedish researchers at Umea University show that this is not the case in a new study published in the journal The Proceedings of the National Academy of Sciences (PNAS). The results are encouraging since they demonstrate that plans for future biomass and solar fuels production are not limited by this effect.

Do increased oxygen levels limit by ? Is this unique process adapted to the low oxygen levels that existed when photosynthesis evolved nearly three billion years ago? These questions have generated vivid discussions in the academic world. Now Umea researchers together with colleagues at the University of Osnabrueck, Germany, can settle the debate. Increased levels of oxygen in the air do not directly inhibit photosynthesis.

“If photosynthetic productivity was directly inhibited by increased oxygen levels it would have severe consequences. It would limit the plans to use and artificial photosynthesis as future means to produce fuel in a sustainable way, since more photosynthesis by plants, photosynthetic bacteria and artificial catalysts would lead to more oxygen, especially locally within bioreactors or artificial devices” says Johannes Messinger, professor at the Department of Chemistry at Umea University.

In the present study, the researchers employed a mass spectrometric technique together with isotopic water (H218O) to probe the effect of increased concentrations of oxygen on the mechanism of water splitting. Water splitting is a complicated reaction which takes place in a large protein complex, called photosystem 2. The absorbed light energy is used to split two water molecules at a time into one molecule of molecular oxygen and four protons.

“We increased the oxygen pressure up to 50 times over ambient conditions. This did not lead to a block of oxygen evolution from water by photosystem 2,” says Johannes Messinger.

Researchers at Umea University’s Solar Fuels Environment as well as other researchers worldwide are trying to unravel all required details from the photosynthesis. Their goal is to be able to build manmade devices that, by employing the same principles as photosynthesis, are able to store solar energy in fuels such as hydrogen or ethanol.

Photosynthesis by plants and certain bacteria uses the energy of sunlight to split water into molecular oxygen, and to reduce carbon dioxide to the carbohydrates we eat. This process evolved about 2-3 billion years ago, and has been the basis for life as we know it. Basically all the oxygen in the Earth’s atmosphere was generated in this way and also most of the biomass, from which parts converted by geological processes into coal, oil and natural gas.

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More information: Membrane-inlet mass spectrometry reveals a high driving force for oxygen production by photosystem II
Authors: Dmitriy Shevela, Katrin Beckmann, Juergen Clausen, Wolfgang Junge, and Johannes Messinger
www.pnas.org/content/early/201… /1014249108.abstract

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not rated yet Feb 17, 2011
Maybe I'm missing something here, but any oxygen produced by photosynthesis would be consumed by burning the biomass to produce energy, with a net effect of zero on the oxygen levels.
not rated yet Feb 17, 2011
As they said:
, photosynthetic bacteria and artificial catalysts would lead to more oxygen, especially locally

You'd get a local increase while the global balance stays roughly* the same.

*Only roughly since if you start increasing the concurrent biomass of the planet this would mean a higher total fixture of hydrocarbons in plant matter with an attendant higher atmospheric oxygen level. Since the CO2 content of the amtmosphere is 0.04% even if you locked all that in biomass and replaced it with O2 from plants the net O2 change would be negligible (up to 20.84% from currently 20.8%).

I think locally (at the site of a biomass concentration) you'd get an increase of probably no more than 1 or 2 percent in the 'worst' case.
not rated yet Feb 17, 2011
Some independent studies have even shown that slight increases in oxygen levels would make the environment for favorable for animal life.

In the past when oxygen levels were higher, there were gigantism in animals and insects, because higher oxygen pressure makes respiration more efficient.

Of course, too much of a good thing can be bad, but we're nowhere near toxicity levels in oxygen.

I suspect that once we get completely off "fossil" fuels, CO2 levels will actually drop dangerously LOW within a century or so.
not rated yet Feb 18, 2011
Quantum Conundrum: Would you mind expanding on that a bit? CO2 levels certainly managed to be stable (well, on human timescales) before we started burning oil and coal reserves, but if I'm interpreting what you're saying correctly (I take it you don't mean that a return to preindustrial levels would be dangerous, and from what I understand even that isn't likely following a hypothetical cessation of CO2 release), you think that for some reason CO2 levels would suddenly plummet?

And, erm, why the quotes around "fossil?"

Anyway...Hrm. I suspect I don't understand this paper; I thought it was pretty well established that oxygen DID limit photosynthesis, what with all the energy plants are forced to waste carrying on photorespiration. The more oxygen, the more Rubisco gloms on to the wrong molecule. Isn't that why C4 and CAM plants evolved in the first place?