If it's true that plants prefer NH4+ and need to expend energy converting nitrate to NH4+ before using it, and they take in NH4+ faster than they will the same amount of nitrate, would it not make sense to have as little biological filtration as possible on a planted tank - thus making more of the nitrogen available to the plants as NH4+ instead of the plants competing with the biological filtration for NH4+ and then having to resort to nitrate for their needs? Would this result in faster growth? On a low tech tank, of course, since we wouldn't want to have to fertilize NH4+ due to the algae issues it may present.

NH4 is highly toxic and must be rapidly converted into Glutamine endogenously/internally. So they cannot have much around inside........on the other hand, NO3 is very non toxic and they can store vast amounts in the central vacuole.

So you also need NO3- as an anion to balance K+ in there also. the plant can then draw NO3 out as needed rather than depending on the environment for a steady supply of NH4, which often varies widely and is typically very low in planted tanks(with or without a bio section).

Also, while it is true that plants expend some effort to convert NO3=> NH4 to glutamine, it's not that much of an energy loss over all.

Uptake or conversion of CO2, photorespiration etc are much larger issues and draw far more energy in terms of of plant energy budgets than does N conversion.

Plants can do this reduction at their leisure as well.

The other thing to consider: algae prefer NH4 as well and the form of N makes a much larger difference to algae. Why do you think that is?
Carbon......algae have far less demand for CO2 than any plant, so NH4 is really a good form of N to have for them relative to a plant. They are a single cell also, so that small amount of NH4 is worth much more than to a large plant with it's higher CO2 requirements, large storage capacity etc.

Most every plant out there also prefers a ratio of NH4:NO3, not this either or business for optimal growth.

Give the toxicity and algae related issues with NH4, I'd rather have a tad less growth(I've never been able to see any significant differences between NH4 and NO3 dosing, nor have any other folks), minimize algae and reduce the toxic effects of NH4 on critters personally.

That's a very very very small trade off, one I've not seen quantified with algae and other critters present.

If you look at the cited reference from Diana Walstad's book, the figure starts off at 2 ppm of NH4, pretty darn toxic.

Then once the level drops to 0.5 ppm of NH5 or close, the rate slows way down.

At that same time, the rate of NO3 uptake starts. and it never stops even when the NH4 is still present.

So under our typicaly aquarium conditions, that graph supports that NO3, not NH4 is actually preferred in Egeria. One plant also is hardly evidence that all 300 species prefer the same conditions as well.

Note, the experiment was also done in absence of any algae spores etc, sterile conditions............our tanks have algae spores and bacteria growing on all surfaces. When you factor such issues into the real world field test vs a controlled lab setting, the results often are no longer significant.

Poor interpretation of graphs can lead to poor conclusions also.
It depends on where on the graph you are discussing.

At one end of the graph, yes, there appears to be preferences for NH4 vs NO3.
However, at the other end of the graph, this relation is reversed.
And that is the end that applies to us and aquariums.

Most research is this way, you have things change through time, space and concentrations etc. You need to be able to apply the research you read and support the argument that you make.

Like the new GI bill study that was recently lamblasted by a certain prez candidate as reducing military personnel serving by causing many to leave to go to college (16%), but then failed to mention that it would attract 16% in new recruits. So they claimed it would reduce membership in the military and should be defeated. I guess they did not or could not read more than the 1st part of the study? In which case I'm very worried, or that he did, and chose not discuss that part that did not fit in with his agenda. In which case I'm even more scared. It was a rather simple study to read, not too technical.

16%- 16% =0%, or no net loss and the study even said this in the conclusion.
And happier more educated GI's.

Political manipulation of Science has a long history and this is done more often than not. You need to read both sides/parts and acknowledge what aspects you feel are applicable to the real world situation.

Same deal here. At first, it sounds like a reasonable argument.
However, unlike politics and extreme cases, I think that was no bad intent on anyone's part, just over looked the graph. Took me a awhile to see the error myself.

Think about CO2 fixing enzyme Rubisco and how much N it demands.
Simply allowing the plant to be more efficient by providing good stable CO2 levels can radically alter the demands for NH4/N in general, thus leave plenty of energy available for growth.

Likewise, in a non CO2 situation, the rates of growth are much slower, thus N demand are much slower, 10-20X less, so the fish waste etc add plenty in the form of NH4.


Regards,
Tom Barr

Another more simple question: would you rather make a system that has less NH4 in case the plants faltered for some reason(say CO2 variation) , or one that is solely dependent on plant uptake?

What happens if you pruned say 705 of the plant biomass back the next day to the NH4 levels?

I'd rather have a good biofilter and backup for NH4 vs having a tiny bit more for the plants. If anything, I generally want to slow growth, but do it via lights.

Regards,
Tom Barr

I experimented with an el natural tank a while back and it ended up with major algae problems. After starting a water change/fertilizing regimen, the algae lessened substantially. I have also noticed in my other tanks that if I slack off on water changes, the first symptom I will see is algae growth of one kind or another. I'm wondering why this would be, I was thinking that it was due to the buildup of organic matter and thus somehow fueling the algae growth, but I can't seem to find an answer in more specific terms. One idea I've had is that the organic waste breaking down in the substrate, is releasing more ammonia and thus providing a constant low level of ammonia to the tank, which according to your logic above, would do much more to fuel algae than the plants. Are there any studies that you are aware of, that show what plants do as far as ammonium uptake, at very low levels (nearly undetectable)? Is it possible that plants will actually not use ammonia at all at levels of around 0.1 or 0.2....and therefore the water changes were both reducing ammonia in the water, plus reducing the waste generating ammonia, and thereby reducing algae problems? But then, the question that would bring up, is that in a cycled tank, any excess ammonia that waste in the substrate is producing, should be cycled into nitrate fairly quickly as the bacterial colony expands to accommodate this gradual change. So that theory doesn't seem to fit both cases.

There's a problem with very low levels of NH4 and uptake testing.

You cannot do it with most methods.
Resolution at low levels really does not tell you much/cannot tell you much.
Also, NH4 is taken up very rapidly by many biota and cycled into various groups.

The only way to look at this is to use stable isotopes like N15H4, or N15O3 and dose to a controlled system and then measure where it goes. No one has done that yte.

I suggested it many years ago.

Water changes do a few things, increase circulation to slow moving areas, adds CO2, O2, disturbs existing algae, removes spores, organic fractions of N etc.
Light is also a factor, more = less stability in terms of plants vs algae.

NH4 is linked to several other factors, it's a path/net, not one cause.

Folks had added NH4 and done fairly well with it, but daily dosing, lots of water changes have also been part of the game as well.

Non CO2 methods should not induce algae unless you really did something wrong.
Generally too much light, doing water changes etc, not enough plants etc.

Many aquatic systems have very low, but constantly resupplied or such large volumes, that plants cannot remove it. Both for NH4 and NO3.

Then you have sediment based NH4 sources as well.

So you can add it to the sediment and then NO3 to the water column.
Which is what ADA seems to do. Where it's added also can make a difference in growth.

Regards,
Tom Barr

Hi everyone.

My first post here, and I hope you don't mind me contributing to this conversation. I'm very interested in this topic, having just started learning about the "el natural" (Walstad, though I'm sure she wasn't the first to make such aquariums) approach to planted tanks. So I was discussing this stuff in another forum, and Carissa linked to this interesting thread.


Do you happen to have some references for the studies about this ratio, or what might be the optimum such ratio, for aquatic plants? My understanding so far is that aquatic plants are quite different to terrestial plants in this regard, though I don't know enough about it to understand why the differences exist.


Agreed that data must be interpreted correctly, or at the very least sensibly, to give a useful result. But I suggest respectfully that you might need to check that graph again. I've just been staring at it (and at the original paper it was copied from - the joys of having access to a university library). And I draw a different conclusion to you.

I agree that a study of one species doesn't necessarily apply to all species, and I haven't checked the original references for the following figure in Walstad's book, which list 29 plants that prefer ammonia and 4 that prefer nitrate.

Note that both figures are in this article, as Figure 1 and Table 1 respectively:
Aqua Botanic - Plants and biological filtration

Anyway, the graph showing data for elodea nuttallii starts off with 2ppm of nitrate and ammonium, and the ammonia is reducing quite fast. The nitrate isn't reducing at all. This continues until the 16-hour mark, when the ammonium is at 0.5ppm and the nitrate still at 2ppm. At this point, the nitrate also starts reducing, but slightly slower than the ammonium is reducing. This continues until the 32 hour mark, when the nitrate is at about 1.5ppm and the ammonium at about 0.1ppm. From this point the ammonium level is constant and the nitrate level decreases slightly faster than before. At the 64 hour mark, the end of the plot, the nitrate is at 0.5ppm and thr ammonium still at 0.1ppm.

I believe that this shows that the plant in question, in the conditions it was in, preferred ammonium over nitrate at least until the ammonium concentration was 1/20th of its original value (0.1ppm). It was only at this point that the nitrate consumption was faster than any ammonium consumption.

I would also guess, by the way, that the experimenters didn't have a way to measure ammonium accurately below 0.1ppm, and that this is why the graph tails off like that, with the ammonium levels constant and low, but not zero. It doesn't seem likely to me that the plants would suddenly stop taking in ammonium altogether.

A quick googling suggests that modern instruments, like the one described here:
Nitrogen Trichloride
can measure ammonium accurately down to around 0.05mg/l. Which makes a lowest value of 0.1mg/l from a study done 18 years ago seem plausible, as instrumentation has probable improved in that time.

My conclusion from this graph is that the plant studied prefers ammonium to nitrate in all conditions where the ammonium level is equal to or less than the nitrate level, though when the ammonium concentration is below 0.5mg/l for a nitrate concentration of 1.5-2mg/l, the preference is slight. When the ammonium gets very low (undetectably low?), the rate of nitrate consumption increases slightly.

I am personally increasingly inclined to rely on plants to remove ammonia from my aquariums rather than on massive "artificial" biological filtration. It will always be a combination of things, of course, but it seems to me that the plants are more reliable and less likely to fail very suddenly than the filter. If the powerhead driving the trickle filter on my largest tank (a measly 30 gallons, I know it's tiny compared to many, but all I can fit) dies, the plants will still grow (yay plants . And once I move my tanks over to getting a lot more natural light rather than artificial light, I won't even be relying on electricity to make them grow well. It seems like a much more stable system to me. (Maybe this is just my lack of experience showing here, though )

Anyway, thank you for having a most interesting discussion in public where people can contribute.

Helen

Is this not why reef aquarists use a refugium? As a natural, planted biofilter? A specialized sump, in a sense.

I suppose one could do something similar for a freshwater planted tank. Put in the "ugly" plants that suck up nutrients quickly like duckweed, or fast-growing weedy substrate plants. Unusual, but interesting.

Jason,

Many ponds now take this approach with a natural algae/duckweed/plant filter.

It is practiced here in FL as it is copied from the natural wetlands process in the glades..........We have finally figured out that Nature does sort of know what it is doing lol

Some farms now use heavily planted areas to filter the water they used to fertilize the crops which are heavy in nutrients and have shown that the levels of nitrate, phosphate, etc are lower than that which came in to them.

It seems to me, from that graph, that the plant preferred ammonium until levels hit at or below 0.5, at which point it had no preference and took both in roughly equally....if we assume that ammonia levels were probably 0.1 or less, and not exactly 0.1. If we assume that ammonia was actually stable at 0.1, then it had nitrate preference by the time it got down to that level.

I think maybe the bottom line is that this graph doesn't provide enough data to make the assumptions that are being made. All it's telling us is that if you happen to have a tank with 2ppm of ammonia and 2ppm of nitrates, the plants will use much of the ammonia first. Maybe, this could be generalized to say that if you have a tank with equal amounts of ammonia and nitrates, this would occur. But what if we started with 0.5 ppm of ammonia and 20 ppm of nitrates (a more realistic situation in an aquarium)? Plants are very good at adapting to their circumstances, so my guess would be that you would see what could be interpreted as a definite nitrate preference under those circumstances....in other words, the ammonia wouldn't be reduced to near 0 before nitrate started being used, both would probably be used concurrently.

Therefore the real question is - is there a benefit to keeping nitrates low enough and reducing the biological filtration to cause the plants to take in a much larger percentage of their nitrogen as ammonia? Can plants actually take in ammonia significantly faster than nitrate? Do the plants benefit in any other way from taking in ammonia instead of nitrate? If not, there is no benefit in avoiding biological filtration (unless someone wanted to, for other reasons not having to do with the health of the tank).

The discussion above, around and below table 2 in
Aqua Botanic - Plants and biological filtration
answers some of these questions, assuming the research done is good (I haven't bothered to look up the refered papers to check the original research).

As I see it, the more interesting things in that discussion are the following:

- as little as 0.02ppm ammonia was enough to inhibit nitrate uptake by duckweed, so that plant at least prefers ammonia so much that it basically won't consume nitrate at all unless there is no ammonia available

- looking at table, 2, the variation in speed of uptake of ammonia is much larger than that of nitrate. It takes hardly more time for the plant to remove 26mg/l of ammonia than it does to remove 0.025mg/l. But for the nitrate the duration to remove 26mg/l is much longer than to remove 0.025mg/l (actually, the detail of that set of data is interesting - looks like there is some kind of threshold around 6.4mg/l of nitrate above which the time taken to remove it is roughly proportional to the amount of nitrate there is, whereas below that point it isn't proportional at all, and for ammonia looks like in the range of that experiment there was no point at which the time taken increased linearly with the amount of ammonia, which is also odd).

Carissa I think that that table 2 actually answers our earlier question about whether plants can cope with a sudden large change in the amount of ammonia available, by the way. If other plants behave like duckweed (of course I don't know whether they do), then a planted tank could presumably deal with a large amount of ammonia (dead fish?) about as easily as the more usual tiny amounts of ammonia. Which is reassuring for me