Re: Photorespiration revisted

["Don Matakis" <dmatakis at charter_net>]

Thomas  Barr  wrote:
> I've been reading some papers and research on PR in algae and higher
plants. Now while some have postulated that variations in CO2 have led to
strategies to deal with PR, from mopst of what I've read seem more to
indicate that variations in O2 levels play a much larger role in PR issue
for algae.
>
> Although I've stated this in the past I've found numerous research
publications to back up my claims regarding why algae declines in a plant
tank when the plants thrive.
>
> Low or high CO2 levels do not influence the ability of algae to handle PR
since many have excellent CCM(Carbon concentrating mechanisms).
>
> But, O2 levels really influence PR in algae much more so.
> When algae PR, they often leak the by product of PR, P gylcolate in a
process that consumes O2 and gives off CO2(A reverse of sorts to that of
photosynthesis) and it loses much of carbon it has fixed.
>
> P glycolate is a strong inhibitor of photosynthesis. So higher
concentrations will cause a decline in photosynthesis. Plants recycle this
PR by product with peroxisomes. Many algae don't have peroxisomes but many
have peroxisomal like pathways to deal with PR from higher CO2 levels but
these pathways are not nearly as efficent when high levels of O2 are
added(say by high plant or algae production).
> P Glycolate is an inhibitor in regulation of RUBISCO and activation of
RUBISCO.
>
> Adding O2, CO2 and a combinations of each at 200% saturation, amibent, 50%
and 5% ambient to algal cultures should show that O2 is a stronger influence
in controlling growth of algae.
>
> This type of experiment would remove the potential plant influences and
focus in on O2 and CO2 levels that are often typically found in planted
aquariums.
>
> One idea I've thought that is a likely mechansim for algae not growing
well is a "back up" when the algae are PR-ing due to CO2 being added. This
drives the algae "too fast" and they are typically using HCO3 as their DIC
carbon source. This takes a fair amount of energy to drive this, and if the
algae no longer use this energy, it is likely that it backs up and lower the
efficiency a great deal.
> Some research indicates that the CCM in algae prevents the formation and
excreation of large amounts of P glycolate(Tolbert 1992). So if you alter
this, it will harm the algae's abilty to grow. CO2 can help but O2 will
likely do much more harm.
>   Some paleo O2/CO2 levels around the time of higher plants show some
interesting patterns.
>
> Interestingly, aquatic plants also leak out P glycolate as well.
> But they and Chara have better methods of regeneration of P glycolate than
most green algae(Mitochondrial pathways vs peroxisomal).

Don't stop now! This is getting very interesting. It's like having your own
researcher right in your living room. While I am a layman when it comes to
the semantics to a point, this is exciting stuff! Kasselman recounts an
experiment where the O2 levels were artificially increased using oxidators.
The aquariums were then observed over several years. She states: Not only
was a visibly improved plant growth registered but another positive side
effect developed, namely the growth of blue green algae being completely
terminated in a few cases.She goes on to say, this context is clear-cut; the
reasons for it though, remain unexplained. In the studied aquariums only an
occasional fertilization (every four weeks at most) was necessary, and not
as a consequence of nutrient oxidation but because of an increased nutrient
consumption due to the strong growth of the plants. So based on these
observations, not only will increased O2 levels aid in the possible
elimination of algae, but promote stronger growth as well. I await further
investigation with anticipation. Interestingly, my oxygen levels in my main
tank are considerably higher than the others, and while other factors of
course play a part as well, I have never had anything in the way of algae
other than glass, and greenwater right after setup while the other tanks
have had it all from time to time. Regards, Don Matakis