That is a very good mind experiment! I like it.

Excellent explanation, Jeremy ... thank you.

Ok just checking my understanding..... this wouldn't work because a million parts of air shall we say are much bigger in volume than a million parts of water because air is far less dense, so you would have to be driving a ridiculous amount of air through the tank to get close to beneficial effects?

Valid common question.
One that gets most folks if you asked at the AGA convention say...........
I do not think more than a few folks might even be able to answer it well.
Simple logically question as well.

Those are often the hardest, but you can gain a lot from them and pursuing the answer.

Folks had long thought they knew everything about CO2.
Yet I keep finding new stuff to apply.

Do not feel shy about not knowing anything.
Ask without reserve.



Yep, the % can and does vary, say at cooler temps, at less light illumination times, you can drive the % of O2 to CO2 up to 100% for respiration- this is the light compensation point.

Plant is just hanging on.

You can drive it more the other way by adding more light/longer times(up to a point) and say have only 10%.

You can also drive the O2 to toxic levels that kills fish, plants, algae etc.
Not typically in our tanks, but does happen in nature at times.


No, the amount of O2 needed and the levels can be very low for plants, they need far less than critters.



Generally high O2 is bad due to photorespiration for plants.
So actually the opposite

Plants do recycle and circulate O2 and CO2.
CO2 from the root zones goes up, O2 comes down to the roots.

Regards,
Tom Barr

Tom,

Oh, this is getting really interesting now. Okay, I think this is all starting to make some sense to me, but like usual the more I learn the more questions I end up having . It is kind of funny how growing in wisdom actually makes you feel humble, because you end up realizing how little you actually know, haha.

I have only been looking into photosynthesis and respiration and seeing them as two unique processes within a plant, and when they are at work they are always doing the same thing. Photosynthesis produces energy for the plant, and respiration requires it, and that's why a plant will slowly whither away if it doesn't get enough light that is above its' "Light Compensation Point" in order to keep the plant in a net gain of energy.

You used the word photorespiration, and now I am confused. I looked it up and tried to understand the meaning of that a bit, and now it is seeming like a third process "photorespiration" occurs, but only when the light levels are high?

It is seems now like photorespiration is a reaction that occurs just because of the fact that the rubisco enzyme can actually accept CO2 or O2, not that it is really a process the plants needs or even wants. Is that correct? Does the plant gain anything at all from photorespiration?

Rubisco accepts a CO2 molecule during photosynthesis, it goes through the Calvin cycle within the plant, and then ends up back where it started as a free and once again usable rubisco enzyme, and the result of those three steps is a net energy gain for the plant. That cycle then just continues over and over during photosynthesis.

Now, if light or oxygen levels are high, a kink in the system occurs. A rubisco enzyme can (unintentionally?) pick up an oxygen molecule instead of a CO2, and if that happens the plant actually has to expend energy to shed itself of that oxygen molecule before that same rubisco enzyme can be used to try to grab a CO2 again? In other words, photorespiration would be the equivalent of someone spending energy to go fishing and being hindered in their pursuit by catching lots of trash from the bottom of a lake on their hook instead of fish?

Does that mean that photorespiration is occurring when plants are pearling, and/or is it a factor at all if the plant isn't pearling? Pearling would then indicate that tank conditions (circulation, oxygen levels, light levels, etc.) are causing the plant to get behind in its' ability to have the waste products of photosynthesis pulled away from the plant leaves and now photosynthesis efficiency is being lessened (possibly dramatically) because of photorespiration taking place and clogging rubisco receptors (with O2 instead of CO2) and lowering efficient CO2 uptake?

If so, wouldn't that mean that pearling is something that is actually hindering growth instead of an indication of it? To put it another way, you would need rapid photosynthesis occurring to even see pearling to begin with, so pearling is still an indicator of good nutrient levels and tank conditions overall, but once you do see pearling it is actually an indication that the plant is beginning to lose efficiency due to photorespiration now coming into play?

Wow, this is getting more interesting the farther I dive into this stuff. I feel like the more little tidbits of this stuff I can grasp the better I can "read" my tank and make small adjustments to optimize everything.

The stuff I read seemed to indicate that photorespiration can actually cut the plant's efficiency of photosynthesis by as much as 50% when it is a factor. That would indicate to me that there is possibly a lot of plant growth to be gained (under the same light levels) if the by-products of photosynthesis (elevated oxygen levels in the tank during the day) could be dealt with somehow and brought down from supersaturated levels. Is that a correct statement? Is there any way to do that without losing the needed dissolved CO2 in the process?

Wouldn't that be a side benefit to having a rich aerobic substrate with lots of bacterial action, because the bacteria could use up a lot of that extra O2 in the aquarium and even add CO2 to the tank water as a side benefit. The bacteria would be helping to increase CO2 and also to reduce the effects of photorespiration at the same time? Or alternately instead of having a rich substrate, wouldn't that be a definite benefit gained from having a large bio-filter in the aquarium?

Have a good one, Jeremy

P.S.- That got me thinking heavily about mazzei's again. If the mazzei's are actually providing the CO2 to the plants in a micro-bubble gas state by sticking CO2 bubbles to the plant leaves instead of relying on actually dissolving the CO2 in the water, couldn't you then heavily aerate the tank water (in the sump for instance) in order to drive off the supersaturated oxygen in the tank water? You would only risk losing the dissolved CO2 in the water, never the micro-bubbles of CO2, so the aeration wouldn't hurt the available CO2 the plant receives as long as the micro-bubbles are numerous enough, and also able to stick to every one of the plants in the tank to provide each of them their needed CO2. That would take some fine tuning of flow patterns and stuff to distribute all the CO2 mist evenly, but it would allow you to minimize the energy loss (to the plant) associated with photorespiration causing the rubisco enzymes to process an O2 molecule when it really wanted to find a CO2 one instead. I would think that would give you a huge possible increase in plant growth since photorespiration can hinder photosynthesis tremendously if the conditions are right for it to occur. Would that work?

^ one point further to the above....if excessive O2 at the leaves is not a good thing, wouldn't increased circulation also benefit the plants by removing the pearling?