# [Wet Thumb Forum]-C3, C4 and CAM photosynthesis



## Tyrone Genade (Jan 1, 2005)

Hello all

Does anyone here know which aquatic plant families do or do not practice C3, C4 or CAM photosynthesis? I can't think of one that doesn't practice CAM photosynthesis...

Thanks


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## Roger Miller (Jun 19, 2004)

> I can't think of one that doesn't practice CAM photosynthesis...


Where are you getting your information?

Roger Miller


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## noah_greenberg (Aug 20, 2004)

Your post made me think and Im not sure that there are any major patterns that will answer your question. I can put wrenches in your statement about the presence of CAM in almost all plants:

To throw one out there that is only capable of C3 would be Riccia, it is a bryophyte and has no water conservative photosynthesis. 

The literature states that CAM photosynthesis is more common in vascular plants than C4, although the only plants known to be C4 are flowering plants. 

In general, the overwhelming majority of plants are C3 only. C4 has evolved multiple times throughout the evolution of plants and is present in multiple lineages of plants. It appears to be selected for in hot and dry environments. I doudt that there would be more than a few C4 plants that are commonly kept in aquaria since most plants would revert back to the more effecient C3 photosynthesis in the presence of water. 

Let me know if this sounds off track.

Out of curiosity, why are you interested in this topic??


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## Roger Miller (Jun 19, 2004)

> Let me know if this sounds off track.


Not necessarily off track, but missing one point.

Aquatic plants may use C4 or CAM because both metabolisms suppress photorespiration and make more efficient use of limited CO2 supplies.

My impression was that CAM is limited to cacti and succulents. Is it more widespread than that? I also thought that C4 was a fairly widespread adaptaton in arid-land plants and also fairly common among algae and aquatic plants.

On the other hand, most of our aquarium plants are close relatives of common terrestrial plants. On that basis alone I expect the majority of our aquarium plants to use the C3 pathway.

Roger Miller


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## noah_greenberg (Aug 20, 2004)

Thanks for the help Roger, CAM photosynthesis is mostly found in cacti and succulents but is utilized by some plants that we might not think of. Two examples are the Pinapple plant and Spanish moss both of which are members of the Bromeliaceae. Another plant that has CAM that is one of my favorite aquatics is Isoetes (quillwort). 

As for wether C4 or CAM is more common, I am going to stick with the opinion the Botany Text book written by Peter Raven that claims that CAM is more common than C4 in the vascular plants. Algae may be different. 

One thing that I constantly need to remind myself of is that the vast majority of the plants we grow in aquariums are secondarily aquatic and have evolved from terrestrial plants (as you stated), so once you begin to compare the loosely related group of plants that are aquatic it becomes increasingly difficult to make generalizations about physiology and habit.


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## Tyrone Genade (Jan 1, 2005)

I've left this thread alone for a few days to see where it goes... I'm unhappy to see that there seems to be just as much ignorance (in respect to what photosynthesis our aquarium plants use) among the professionals as me.

Here are a few refs:


> *CAM photosynthesis in submerged aquatic plants.*
> 
> _The Botanical Review_ 4/1/1998; Keeley, Jon E.
> 
> Crassulacean acid metabolism (CAM) is a [CO.sub.2]-concentrating mechanism selected in response to aridity in terrestrial habitats, and, in aquatic environments, to ambient limitations of carbon. Evidence is reviewed for its presence in five genera of aquatic vascular plants, including Isoetes, Sagittaria, Vallisneria, Crassula, and Littorella. Initially, aquatic CAM was considered by some to be an oxymoron, but some aquatic species have been studied in sufficient detail to say definitively that they possess CAM photosynthesis. [CO.sub.2]-concentrating mechanisms in photosynthetic organs ...


and at the bottom of this page.

To the first reference you can add Lobeliaceae (the family to which Rotala belongs) into the mix as well as plant that practice CO2-concentrating. I haven't found anything about the mosses anf ferns nor Araceae etc... But most plants I can find info on seem to practice CAM.

Cacti, arctic/antartic and aquarium plants all have the same problem: low CO2. The 2 former because if they open their stoma they will dehydrate and the latter because there is very little CO2 in water (period). It makes sense for them to have adaptations to cope with the situation. It seems few practice C3 and many may practice something like CAM (but isn't).

My question, still is, which aquarium plants cannot practice CO2-concentration? We have one: Riccia. Are their others?

This whole issue popped into my head after fighting with several people because: if most plants do not practice C3 photosynthesis then that means they DO NOT release CO2 in the dark but instead store it so plants cannot smother the fish with CO2 at night. This was a totally lunatic concept to most as school textbook only seem to deel with C3 and so I'm obviously mad... My main arguement is that any such "suffocation" problems with CO2 at night would be from the drop in pH caused by synthesizing the acids. This would cause acidosis in the fish which is totally different from CO2 suffocation.

Your thoughts?


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## Roger Miller (Jun 19, 2004)

One of the reviews I came across said that CAM has been identified among 33 different families. That would cover terrestrial and aquatic plants and it might even include algaes, since much of the literature is very lax about the distinction. In some cases that is adaptive CAM and in others it is constitutive. In either case, identifying CAM in one or two plants in a family probably does not imply that all the related plants have the same ability. Considering that most of the CAM plants are terrestrial, the existence of CAM in 33 families does not suggest that a vast number of aquatics will be CAM plants.

In addition to the list of plants you found, you can add Lobelia. According to one reference I read L. dortmanii has CAM. That does not mean that L. cardinalis does as well, but it opens that possibility.

Among aquarium plants where I would look for CAM I would probably look first at the Aracaea. I've seen both A. nana and C. wendtii growing and healthy in sunlit aquariums with the pH over 9. That capacity suggests to me that CAM may be involved.

I do think you're asking the wrong question, though. CAM is more common than it was once believed, but generally it is not as common as C3. The presumption has to be that plants don't practice CO2-concentration. Your question then should be, which plants do practice CO2-concentration, not which ones do not.

People have experienced fish suffering from high CO2 levels in heavily planted aquariums after periods of lights-out. More often people simply observe that pH rises with lights on and falls with lights off. In view of those basic observations it would be difficult to argue that all aquarium plants -- or even a majority of aquarium plants -- use CAM.

If all else fails you can try using the traditional approach to identifying CAM plants. Taste the plants in the morning after the lights come on, then again in the evening. A CAM plant should taste more acidic in the morning than in the evening.


Roger Miller


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## noah_greenberg (Aug 20, 2004)

> if most plants do not practice C3 photosynthesis then that means they DO NOT release CO2 in the dark but instead store it so plants cannot smother the fish with CO2 at night.


Would you mind explaining this idea? Are you supporting this point of view???


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## Tyrone Genade (Jan 1, 2005)

Simply put, I do not know. That is why I asked. 

From the small amount of literature I have found (and the in-class comments of my Botany prof who studies CAM photosynthesis) my assumption is that most aquatic plants are CAM plants. And to date I only have the one example of Roger saying otherwise.

From my own observations I have only ever seen heavy O2 production in the morning from my plants kept in well aerated tanks suggesting CO2 accumulation at night. These plants were indian fern and Hygrophilia polysperma. (I was employing UG filtration so the Crypts never got anywhere...)

Given the inherent low CO2 levels in water and the fast growth of some aquatic plants in conjunction with the observation that my Hygrophilia stopped photosythesizing by mid day (as evidenced by them reorientating their leaves out of the direct light: going from -- to / relative to the light |) leads me to tentatively assume they stock piled CO2 at night and spend it all very early on in the day.

In one such tank there was a pr of Neolamp. sp. daffodil and about 60 fry in probably only 35 L with only a small box filter and heavy Lemna growth at the surface hampering gaseous exchange. I never saw any sign of CO2 asphyxiation... So again I must conclude the plants (there were stacks of hornwort and Hygrophilia!) must of been concentrating the CO2 at night.

Generally my planted tanks were heavily stocked with very little water movement (if any) and I never seen any CO2 asphyxiation problems. What I have seen is pH problems that cause the fish to gasp at the surface due to acidosis, or from the plants using up all the available O2.

For those who report CO2 suffocating their fish I would like to see the CO2, pH and O2 readings... because it is my belief that it is the O2 and/or pH that is the problem.

This is of course speculation, and would greatly appreciate any hard data backing this up or flat out refuting it.

I would like to take Roger up on his acid test, but as I can watch the snails dissolve before my eyes in my desk tank I doubt I could decern any additional acid taste in the plants.

Thanks for your input. I will also get in touch with my old Botany Prof and pick his brains.

Regards


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## Roger Miller (Jun 19, 2004)

> Originally posted by Tyrone Genade:
> And to date I only have the one example of Roger saying otherwise.


Raven in "Energetics and Transport in Aquatic Plants" provided a lengthy discussion on CO2-concentrating mechanisms in aquatic plants. He did not regard CAM as a widespread adaptation. In fact, many of the aquatic plants that have been identified as CAM plants may only use CAM facultatively and not express the capacity under common aquarium conditions.



> From my own observations I have only ever seen heavy O2 production in the morning from my plants kept in well aerated tanks suggesting CO2 accumulation at night.


That is a reasonable suggestion, but there is a long step from saying there is CO2 accumulation at night to saying that plants are exercising CAM.

It is common for pH to swing from day to night, being high during the day and low during the night and morning. This is common in natural water bodies with aquatic plants and algae and it is common in aquariums where the pH is not regulated. That variation reflects the accumulation of CO2 _in the water_ at night, and its decline during the day as non-CAM plants use the CO2. Your plants may be photosynthesizing only in the morning because that is when they have the best CO2 supply.

Aquatic plants may also accumulate CO2 at night _in their lacunae_ and other gas filled spaces. I have read that most of the CO2 that plants respire at night actually accumulates in their lacunae; it is reused during the day and little of it actually makes it back into the water. Plants generally use more CO2 then they produce, so the accumulated CO2 is only going to last for a period in the morning.



> In one such tank there was a pr of Neolamp. sp. daffodil and about 60 fry in probably only 35 L with only a small box filter and heavy Lemna growth at the surface hampering gaseous exchange. I never saw any sign of CO2 asphyxiation...


I don't think I've ever seen much evidence for CO2 asphyxiation in planted aquariums without added CO2. In a planted tank with added CO2 the CO2 levels vary over a normal light cycle due to the relative importance of respiration and photosynthesis and are at their highest when the lights come on.



> For those who report CO2 suffocating their fish I would like to see the CO2, pH and O2 readings... because it is my belief that it is the O2 and/or pH that is the problem.


I'm not sure how your going to use those measurements to distinguish between a pH effect and a CO2 effect, since they are interrelated.



> This is of course speculation, and would greatly appreciate any hard data backing this up or flat out refuting it.


Their is lots of information out there saying that C3 is the most common mechanism for photosynthesis. In fact I think that C3 photosynthesis was first defined at least in part in research using aquatic plants (er, possibly algae).

I'm afraid that if you want to argue that a majority of aquatic plants are CAM plants, then you will have to provide the evidence. The presumption has to be that they are not. That presumption is reasonably supported by the common observation that pH levels in planted tanks rise during the day and fall at night. Furthermore if there are only 33 families of plants in which CAM has ever been identified and most of those plants use CAM as an adaptation to arid environments then I don't see much possibility that a majority (much less all) aquatic plants would be CAM plants, facultative or otherwise.

Were I looking for adaptations that aquatic plants used to get a carbon supply in CO2-poor environments I would look to their adaptations for using HCO3-.

Roger Miller


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## Tyrone Genade (Jan 1, 2005)

Hello again,

This is the response from my old Prof (mildly edited to be applicable):



> Aquatic CAM was first described in Isoetes but overnight acid accumulation has been detected in about 160 aquatic and marine species. Many of these are seaweeds or freshwater algae and most show very low acidification.. The species with substantial overnight acidification are the ones you mention (I'm no sure about Lobeliaceae). There is some
> doubt whether plants with mild acidification are CAMming. See JE Keeley (1996), Aquatic CAM photosynthesis (In K Winter and JAC Smith, Crassulacean Acid Metabolism, Ecological Studies Vol 14, pp 281-295)
> 
> Regards to the fish - If the plants are CAMmming then one would not get acidosis. One would get low O2 though. I doubt there is much CAMming going on in an aquarium. In any case it would not deplete CO2 levels that much. I think both CO2 accumulates and O2 is depleted at night, but not to levels that could kill fish - especiually if there is aeration at the same time and the water is mixing. However, it is easy to measure. Get hold of an oxygen electrode and pH meter and measure.


From the some other reading is seems that most plants CAM at night in a faculative fashion as you (Roger) state, but of that "most" plants most are weak CAM idlers and switch to C3 during the day.

So, I'm mostly wrong but also partly right it seems.

Thanks for the info gatherred in the discusion.

Regards


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## Roger Miller (Jun 19, 2004)

Tyrone,

That's all been very interesting. Thanks for following up.


Roger Miller


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