Basic CO2 / O2 Plant Question - (Oct/11/2009 )

Hello,

Thanks for stopping by to read my post.

Any help is welcome.

I have a long-held passion for Plant Biology in general - it just fascinates me.
Although I have been reading under-graduate level books on the matter I am unable to resolve a simple question.

Therefore I would be grateful for your thoughts...


Very basic plant respiration states that plants 'consume' (for want of a better word) carbon dioxide during the day/lights on period,
and oxygen at night/lights off.

It is a common horticultural trick to add supplementary CO2 during the day;
but I wondered how effective supplementary O2 would be for the night, raising O2 levels from apprx 18% to say 60%?

I have read in many places that plants have equal affinty for both CO2 and O2, so how would I 'help' the plant choose
which gas to 'consume' other than by saturating its direct environment with the relevant gas?

These questions have bugged me for a while, and I really would be very grateful for your time of your thoughts.

Kevin

To wnat end would you supplement oxygen? It's not so much a "choice". Fixing cabon dioxide in the form of carbohydrate and respiration of oxygen for energy production are distnct mechanisms. Neither oxygen or carbon dioxide replaces the other.

As I understand it, and am happy to be corrected -

intensive horticulturalists use supplementary CO2 to improve growth (say of tomatoes)
so I am assuming that to provide O2 during the night phase will also be assistive...?


I appreciate that as you say they are distinctive processes and one does not replace the other - I know that.


But what I was asking was, IF there is equal affinity for both CO2 and O2 AND saturating the day time environment
with CO2 is beneficial THEN should the same be true if the growing environment was saturated in O2 during the night phase?


Many thanks for your time to post - I truly appreciate it.

Kevin

Since we agre these serve different processes, "equal affinity" is probably not the right concept.

Suggest you start with the article cited below and work back through the references.

http://www.pnas.org/content/98/5/2473.full

Very Many thanks, George.

I appreciate your time.

Kevin

It should be mentioned that such elevated oxygen concentrations also have the risk of oxygen toxicity, at least with animals. I guess with plants it will be similar, though I'm not sure....keywords are reactive oxygen species and oxidative stress....
And I wonder if increased cellular respiration will have an effect on plant growth. Increased photosynthesis rate with elevated CO₂ concentration is more obvious, if CO₂ is a limiting factor here.

hobglobin on Oct 11 2009, 06:14 PM said:

Yeah, I don't think it will work so much. The growth increase from added CO₂ is due to photosynthesis -which is a gain of potential energy, whereas O₂ is used in respiration which is a loss of potential energy. Adding O₂ at night wouldn't help the plant in any fashion I can see other than to increase the rate of respiration (which is pretty small anyway) thereby increasing the rate at which the plant will use up some of the sugars made during the day.

Annals of Botany 2004 94(5):647-656

Plant Respiration and Elevated Atmospheric CO2 Concentration:
Cellular Responses and Global Significance

􏰀 Background Elevated levels of atmospheric are likely to enhance photosynthesis and plant growth, which,
in turn, should result in increased specific and whole-plant respiration rates. However, a large body of literature
has shown that specific respiration rates of plant tissues are often reduced when plants are exposed to, or grown at,
high due to direct effects on enzymes and indirect effects derived from changes in the plant’s chemical
composition.
􏰀 Scope Although measurement artefacts may have affected some of the previously reported effects of CO2 on
respiration rates, the direction and magnitude for the effects of elevated on plant respiration may largely
depend on the vertical scale (from enzymes to ecosystems) at which measurements are taken. In this review, the
effects of elevated from cells to ecosystems are presented within the context of the enzymatic and physio-
logical controls of plant respiration, the role(s) of non-phosphorylating pathways, and possible effects associated
with plant size.
􏰀 Conclusions Contrary to what was previously thought, specific respiration rates are generally not reduced when
plants are grown at elevated . However, whole ecosystem studies show that canopy respiration does not
increase proportionally to increases in biomass in response to elevated , although a larger proportion of
respiration takes place in the root system. Fundamental information is still lacking on how respiration and the
processes supported by it are physiologically controlled, thereby preventing sound interpretations of what seem to be
species-specific responses of respiration to elevated . ThereforeAnnals of Botany 94: 647–656, 2004
doi:10.1093/aob/mch189, available online at www.aob.oupjournals.org