Do plants really use ammonia? or is that a myth? - The Planted Tank Forum
 
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post #1 of 15 (permalink) Old 07-06-2006, 08:40 PM Thread Starter
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Do plants really use ammonia? or is that a myth?

Does anyone have any proof on this idea that plants use up NH4+ because I have never seen it happen. I have had exactly similar ammonia spike in tanks densely planted and tanks that are not.

I know that the surfaces of plant leaves make very good places for nitrifying bacteria to colonize because of the O2 given off by the plants. I do have tanks that don't have any other bio filtration- just powerhead to circulate the water, and adding plants from an already cycled tank will shorten the cycle time- but I believe that is because they are already covered by nitrifying bacteria, not because the plants themselves use the ammonia as a food source...

This hypothesis comes from personal experience. I have treated for disease in a densely planted tank and wiped out the bio filter with antibiotics. I got a regular 6 week ammonia spike just like I would have in a tank that wasn't densely planted... there was absolutely no difference from a traditional "dry start" cycle (without seeding the filter with established media- or in this case without taking plants from an established tank with a mature cycle)

I had water sprite, hornwort, ludwigia, cabomba, L. sessiliflora, h.polysperma, L. aromtica and duckweed that would cover the top each week in a 180 gallon tank. I dosed with micros and macros on alternating days, 400w of PC light and pressurized CO2 with a 3 foot PVC reactor. The place is a weed factory.

Anyone have any hard data?
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post #2 of 15 (permalink) Old 07-06-2006, 08:46 PM
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A good place to get started is the Nitrogen Cycle.

http://en.wikipedia.org/wiki/Nitrogen_cycle

I believe ammonia is the most preferred nitrogen source for aquatic plants, but addition of ammonia directly is a good way to get green water (First hand experience here.)

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post #3 of 15 (permalink) Old 07-06-2006, 08:47 PM
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From what I've HEARD, ammonia is easier to break down than NO3, which is why the nitrosomonas and nitrobacter bacteria go after it. NO3 is only broken down in anaerobic conditions. It would make sense that plants would use NH3 over NO3 for this reason, but let's wait till Tom Barr or another guru speaks up.


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post #4 of 15 (permalink) Old 07-06-2006, 09:01 PM Thread Starter
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According to the diagram blue ram provided plants can only assimilate Nitrates- and bacteria are the only things listed than can covert/utilize Ammonia and nitrite- but I think that may be oversimplifying...

What exactly do plants "break it down" to for use?

Considering plants need CO2 to grow, that IS anerobic, right?

Also plants release O2 as a byproduct of growth? it would make sense that the O2 woudl come from NO3, right? otherwise they would be releasing Hydrogen if they were using the nitrogen from NH4? no?
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post #5 of 15 (permalink) Old 07-06-2006, 09:22 PM
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There's a nice succinct section in Diana Walstad's book that addresses this well, so I'll just type it up here:

Quote:
Chapter VII, Section 4: "Plants and Nitrifying Bacteria Compete"

Plants, algae, and all photosynthesizing organisms use the N of ammonium (not nitrate) to produce their proteins.

Nitrate conversion to ammonium by plants (e.g. 'nitrate reduction') requires energy and appears to be the mirror image of nitrification. Nitrifying bacteria gain the energy they need for their life processes solely from ammonium oxidation to nitrate; the total energy gain from the two-steps of nitrification is 84 Kca/mol, and the overall reaction is:

NH4+ + 2 O2 => NO3- + H20 + 2 H+

Plants must expend essentially the same amount of energy (83 Kcal/mol) to convert nitrates back to ammonium in the two-step process of nitrate reduction. The overall reaction for nitrate reduction is:

NO3- + H20 + 2 H+ => NH4+ + 2 O2

Plants use ammonium to synthesize their proteins. Thus, when nitrifying bacteria convert ammonium to nitrates, plants are forced—at great energy—to convert nitrates back to ammonium.
And another good little snippet:

Quote:
Chapter VII, Section 3: "Ecology and Nitrogen Source Preferences"

... Nitrate predominates in many drier terrestrial soils. This is because there is plentiful oyxgen, which nitrifying bacteria use to rapidly convert ammonium to nitrates. Nitrates accumulate, because the oxygen discourages nitrate removal by denitrification. Thus, many terrestrial plants, especially crop plants, have adapted well to their nitrate-rich environments, and in general, prefer nitrates or an ammonium/nitrate mixture over pure ammonium.

In the aquatic environment, however, ammonium predominates. This is because almost all sediments supporting aquatic plant growth are anaerobic. Ammonium, not nitrates, tends to accumulate, because anaerobic conditions discourage nitrification and encourage denitrification. Because ammonium predominates in the aquatic environment, most aquatic plant species have developed an ammonium-based nutrition. ...
She also talks about how this isn't true of all aquatic plants... some still prefer nitrates... but it's a small minority.
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post #6 of 15 (permalink) Old 07-06-2006, 09:28 PM
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I think the chart is an over simplification in that Ammonia is used more quickly (tasty, evaporation) so the other form are more available.

The other questions are a mater of the metabolic pathway. Plants (oversimplified) consume light, CO2, and (NPK etc) to make sugars and O2 and animals consume sugar and O2 to make energy etc...

Quote:
Originally Posted by turbosaurus
According to the diagram blue ram provided plants can only assimilate Nitrates- and bacteria are the only things listed than can covert/utilize Ammonia and nitrite- but I think that may be oversimplifying...

What exactly do plants "break it down" to for use?

Considering plants need CO2 to grow, that IS anerobic, right?

Also plants release O2 as a byproduct of growth? it would make sense that the O2 woudl come from NO3, right? otherwise they would be releasing Hydrogen if they were using the nitrogen from NH4? no?

Moved to Tucson.
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post #7 of 15 (permalink) Old 07-06-2006, 09:28 PM
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Quote:
Do plants really use ammonia? or is that a myth?
They don't use ammonia (NH3), but they do use ammonium, NH4+.
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post #8 of 15 (permalink) Old 07-06-2006, 10:20 PM
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Ammonium begins converting to ammonia at when the ph rises above 6.8. Ammonia is toxic, ammonium is not.

The nitrogen cycle charts in my library are split. Some show plants only taking up nitrates and some show plants taking up both nitrates and fish waste. None of them indicate that plants can use the middle stage (nitrite).

It appears that in acidic water, plants use ammonium and nitrate. In alkaline water, the bacteria have to break the ammonia down into nitrites and then into nitrates before the plants can use it.
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post #9 of 15 (permalink) Old 07-07-2006, 07:28 AM
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Cheryl, that sounds logical. Plants utilize whatever is there and whatever is easiest for them. If the conditions are right for them to uptake ammonium, they will do it, if conditions are right for nitrate uptake, they will do that. They are both forms of nitrogen which is the major nutrient all living plants need. If you want to know specifically how plants use nitrogen, you can find it on the net or any biology book. Plants do not use nitrite.

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post #10 of 15 (permalink) Old 07-07-2006, 11:47 AM
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post #11 of 15 (permalink) Old 07-07-2006, 02:28 PM
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Ignoring plants for a moment, I've never been able to make up my mind if it's better to keep it acidic to keep the ammonia from being toxic (ammonium) or to keep it a little alkaline and let the biological handle it. I've found an established biological filter to be pretty powerful at breaking down ammonia and nitrite.

Also, since it's not an on/off switch at a certain ph I wonder if it isn't better to keep the water a little closer to neutral. I've noticed when I forget to buffer my water and the ph in the tanks runs low (6.2 or less) that I seem to get more mulm buildup in the tank and they (plants and fish) seem a little limp compared to when they're around 6.6 or above.
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post #12 of 15 (permalink) Old 07-08-2006, 12:51 AM
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Quote:
Originally Posted by turbosaurus
Does anyone have any proof on this idea that plants use up NH4+ because I have never seen it happen. I have had exactly similar ammonia spike in tanks densely planted and tanks that are not.
A real issue when you measure such levels of NH4 is the test kit itself.
Rather than approaching it that way, actively add NH4 and then you'll know the ppm's you just added as inorganic NH4, this is the most bioavailable form as well.

Then see what the test kit measures, you'll do best to use a very accurate NH4 measurement test method.
I use a spectrophotometer.
This gives me a working accuracy of about 0.01ppm, or 10 ppb.
If I was real careful and played around with a few thing I might cut that in 1/2.

Still, the NH4 that is produced in most planted tanks is consumed as quickly as it's produced by fish, bacterial and fungi decomposition, plant leeching, various tiny microscopic inverts.

So you cannot measure it directly from the water sampling methods normally done by hobbyist.

If you isolate the plant and give it NH4, you can get an uptaker rate of about .5-.8ppm per day.

Problem is that will induce green water unless you also do a large daily water change as well.

Adding 2ppm of NH4 is lethal, so unless you like to dose very small amounts of "fire", dosing NO3 which is literally 500 X less toxic makes much more sense to the water column from which most hobbyists folk think is the only place they should test from(It's not).

Since there is an ample supply of NO3 present and it will not all be removed right away, nor does it induce algae, the test kit method works well and there's a good correlation between water ppm of NO3 and plant health etc.

Not so with NH4.

More is known about the NO3 uptake process in plants than NH4 uptake.
As DW mentions, some plants have preferences. Most simply assume she says that ALL plants prefer NH4, this is not true and even the plants that do have a preference often need a balance between NO3 and NH4 for optimal growth.

Even if the plant needs to use a little bit of energy to reduce NO3 to NH4, this is less of an issue than if the plant is limited by Nitrogen in general.
That's much worse for growth than these differences.
Wheat perfers NO3. Pretty large food crop.

The other issue, and one that seems to have been over looked in DW's interptation of the Graph on page 107, (Ozimek et al 1990).

Each form of Nitrogen was given to a plant, Elodea, and the 2ppm of each NH4/NO3 was measured over the next 64 hours.

The rate of NO3 was supressed, the NO3 was not utilized by the plant until the NH4+ levels had dropped to a little less than 0.5ppm NH4.

Then under these lowered NH4 conditions, the NO3 uptake took off and was faster and the NH4 uptake stopped entirely at 0.1ppm or so while the NO3 continued uptake.

The concentration of both NO3 and NH4 will determine which will be used.
Very low levels of NH4 likely are used by plants and bacteria, but how often do we have 0.5ppm or 2.0ppm of NH4 in our tanks?

Never.

So if you use a citation for support, make sure it applies to the situation and the horticultural constraints we have as aquatic fish hobbyist and folks not wanting algae as well.

NH4 incapsulated in ADA aqua soil or soil, or various other NH4 substrate ferts does work to help gibve the roots some access without getting into the water column, but I lost count at how many folks have gotten a nice algae bloom playing with Jiobes, and other ferts with NH4 in them.

For simplification of dosing, adding NO3 as the sole source alogn with some NH4 in the substrate seems to work well, as long as you do not pull all the NH4 up at once, the ADa AS seems to do this well since the grains are slow to release the NH4 since each grain is it's own functional unit, unlike a layered system when you uproot, it'll make a mess.

The other issue, you get better decomposition and better bacterial cycling if you have a decent grain size and allo O2 down into the substrate, too much mulm is bad and clogs things, as is very fine caps of sand that prevent flow in/out.

Quote:
I know that the surfaces of plant leaves make very good places for nitrifying bacteria to colonize because of the O2 given off by the plants. I do have tanks that don't have any other bio filtration- just powerhead to circulate the water, and adding plants from an already cycled tank will shorten the cycle time- but I believe that is because they are already covered by nitrifying bacteria, not because the plants themselves use the ammonia as a food source...
Perhaps........but Ozimek et al(1990) also did a control set of tanks that showed the bacterial processes had very little influence on the levels of NO3 and NH4.

So...........
I'd stick with the idea the plants are very good at NH4 uptake.

Quote:
This hypothesis comes from personal experience. I have treated for disease in a densely planted tank and wiped out the bio filter with antibiotics. I got a regular 6 week ammonia spike just like I would have in a tank that wasn't densely planted... there was absolutely no difference from a traditional "dry start" cycle (without seeding the filter with established media- or in this case without taking plants from an established tank with a mature cycle)

I had water sprite, hornwort, ludwigia, cabomba, L. sessiliflora, h.polysperma, L. aromtica and duckweed that would cover the top each week in a 180 gallon tank. I dosed with micros and macros on alternating days, 400w of PC light and pressurized CO2 with a 3 foot PVC reactor. The place is a weed factory.

Anyone have any hard data?
Which type of data specifically are you looking for?

Regards,
Tom Barr




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post #13 of 15 (permalink) Old 07-08-2006, 01:05 AM
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I'd like to see ammonia vs. NO3 in terms of plant mass increases.
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post #14 of 15 (permalink) Old 07-08-2006, 02:10 PM Thread Starter
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Wow guys- this is great... I didn't expect so much info,

So plants will use NH4, but something had to be limiting my plants uptake of the NH4+. My ph is under 6.5 in all my tanks, so most of it should have been NH4, but I still lost fish and they still showed massive amounts of stress when I sacked the bio filter, just like cycling a tank without plants- wonder why that was?
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post #15 of 15 (permalink) Old 07-08-2006, 06:56 PM
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Quote:
Originally Posted by 5380
I'd like to see ammonia vs. NO3 in terms of plant mass increases.
There are few that do this, Ozimek et al, 1990 showed this with Elodea.

What has not been done is a ratio of NH4: NO3, they only do one or the other.

Under real life plant tank conditrions, this is the most common condition.
I doubt anyone in our hobby unless they use hydroponic sterile culture perhaps can isolate things enough.

Note: this is for the water column, NH4 levels are higher in the substrate and it's surface, fish poo does not rise, it sinks to the gravel.

As NH4 is leeched, the plants and bacteria get it, it never makes it up into the water column where most test it.

The scale is also an issue, right close to the fish poo, the NH4 will be higher.
At the top of the tank? Lower.

When you move a syringe etc near poo, it'll distrub these micro boundaries/concentrations. Being very careful and slow can get around that and there are other methods like 15N etc.

Not really the realm of the hobbyists though.

Regards,
Tom Barr




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