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Re: Reverse photoperiod filtration?
On Sat, 15 Apr 2000, Tom Barr wrote:
> Do algae use N at night also like the bacteria and plants? To what extent?
> If they do, what the heck is this notion of Reverse Photo period for
> filtration? If the nitrogen is being used up by both the plants and the
> bacteria and maybe algae then why do these companies promote the Reverse
> photo period idea as being an some sort of advantage when using
> scrubbers/filters for N removal?
The most authoritative reference I know of for reverse-cycle filters is
"Dynamic Aquaria" by Adey and Lovejoy. Their content is a little
questionable as far as I'm concerned because they're pretty much
advertising for the Algae Turf Scrubber (R) system. Just the same, what
they say (p. 234) is "While the microcosm is in darkness, the algae in the
scrubber are photosynthesizing, insuring a continual supply of oxygenated
water, and rapidly removing CO2 and nitrogenous waste just when it is most
I can see their argument for evening out the oxygen supply with
reverse-cycle lighting. This would also even out the CO2 demand and
smooth out any pH swing. I'm unclear on the link to nitrogen uptake.
Raven, in "Energetics and Transport in Aquatic Plants" pointed out that
respiratory processes in aquatic plants (mostly he was talking about
algae, but the basic mechanics are the same for plants) are suppressed by
as much as 95% during during the lighted period. That is so the plant's
resources (ATP supply, for instance) can be focused on photosynthesis. I
doubt that the suppression of respiration will happen in roots or any
other non-photsynthetic tissue. Plants use respiraton to get the energy
they use to reduce nitrate to ammonia; they also use molecules produced
during respiration to build the proteins that would use nitrogen. So if
anything, it appears to me that nitrogen uptake by plants and algae should
be *suppressed* when the lights are on.
Uptake and use of nitrate specifically might be a little different. I
read recently that plants can divert NADPH produced in the light reactions
of photosynthesis to reduce nitrate to ammonia. This reduction would
occur only in photosynthetic tissue and only when the lights are on.
Also, nitrate is only one source of nitrogen.
I can see why the reverse lighting cycle is a good thing for the oxygen
supply and for evening out pH swings. But when it comes to any advantage
in nitrogen uptake, all I can say to its proponents is "prove it".