It seems entirely logical that there would be some ‘aquatic’ plants that prefer lower Co2.
In our aquariums, folks are often looking for ‘optimal’ growth and form, whatever that looks like in our eyes. (The plants are probably less bothered about being perfect) Optimal growth conditions are always going to be different for different plants and therefore practical application of our husbandry methods can only be based on finding an appropriate ‘centre line’ for whatever selection we choose to keep.
My question would be, why wouldn’t there be plants that are inhibited by high Co2? Simply on the basis of ‘all things under the sun’ there are bound to be some that fit that bill and the family of obligate aquatic plants, that are never (in nature) exposed to atmosphere and have evolved therefore to live permanently in a lower Co2 environment, may logically contain those candidates.
I’d guess however that there are also obligate aquatics that would do perfectly fine with higher Co2. Figuring out which are which may be entirely dependant on popularity of, or level of desire to keep, a specific plant.
After all, much of the knowledge of how to best keep aquarium plants will come from aquarists so some of these plants may be ‘known’, others not so much.
So, again, with no scientific evidence, you can probably take out any and every aquatic plant that can be successfully grown emersed (makes sense right) so then you just gotta figure out if any of your obligate aquatics perform better with lower Co2 and then, to achieve optimal form, not grow them with plants that prefer ‘high’ Co2. (Oh and then match them to their other optimal parameters, such as nutrient/light levels etc….Easy 👍………ok maybe not!! 😏)
If of course the ‘high’ Co2’ level that inhibits such plants is, in fact, notably higher than 30ppm ish, alot of us can just go back to watching eastenders now. 😊
And anyone that wants to run Co2 at higher than 44ppm and also grow Elodea Densa at optimum, might be out of luck I guess.
As for full, 1/2 and 1/4 Co2. If full is 30ppm (and most folks would consider that to be the case) then there would need to be strong evidence that a number of plants are detrimentally effected at levels lower than 30ppm for that to ever be relevant and I’m not seeing that in this study!
Anything above 30ppm might need a new category. Full plus? super full maybe? 😊 but, as this study allows up to 44ppm (I believe!) I’m still thinking the list of plants that would actively suffer within any range that is normally implemented by aquarists would be pretty small.
Just my 2pennies worth! 😊
As for 150ppm. I’d be interested to see physically how that could be achieved 😳but in a practical sense, seems like ‘Co2 is free’ taken to a whole ‘nother level! 😂