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