[Malawi]

Hi

There was a litle discussion on another board (non english) about what the plants prefer to use as nutrition.

One view was that the plants prefered Ammonia over nitrite, but would use nitrate when the two former was exploited.

The other vie was that the plant prefer Ammonia, cannot use nitrite, but would use nitrate when there was no Ammonia. According to this view the nitrite might pe poisonous to the plants.

Now I hope to get more info on the subject, since there seems to be a lot of knowledge on this forum, I am trying here.
Are one of the former "statements" correct, or is it something inbetween?

 

[Malawi]

Nice question!

First off, plants will use Ammonium (NH4+), not ammonia(NH3). In the biological process, plants will convert ammonium to nitrite by bacteria call Nitrsomonas. Nitrite is usually very quickly converted to nitrate, by more agressive bacteria, Nitrobacter. Nitrite is known to be toxic to terrestrial plants, even at low levels. The same is true for aquatic plants. So plants can utilize nitrogen either in the form of ammonium or nitrate. Some plants have a preference of one over the other, but most don't.

I am used to just using the term Ammonia, although this is as you say not completely correct. I will try to distinguish Ammonium/Ammonia as there clearly are a difference.

I may be out on a limb here, but I feel pretty confident that the plants can take up ammonium without help from bacterias. And that ammonium to nitrite convertion only happends by bacteria if there are not enough plants to absorb it.

The third point in this paragraph goes right to the core of the discussion I refered to.
In the link bgzbgz posted, there are a small section about it, and a graph (fig 3)

I'll just paste the section here, since this is what the debate revolved around.

--Snip--
Nitrite Uptake by Plants

Although plants can use nitrite as an N source, the pertinent question for hobbyists is- Do aquatic plants remove the toxic nitrite before the non-toxic nitrate? I could not find enough studies in the scientific literature to state conclusively that they do. However, the chemical reduction of nitrites to ammonium requires less of the plant's energy than the chemical reduction of nitrates to ammonium. (A plant must convert both nitrites and nitrates to ammonium before it can use them to make its proteins.) Thus, it is not surprising that when Spirodela oligorrhiza was grown in media containing both nitrate and nitrite, it preferred nitrite (Fig. 3).
--Snip--

As one can see, this suggests that nitrite may be benificial to aquatic plants, even though it is considdered poisonous to surface plants.
It may be a measuring error (maybee there were nitrobacters in the sample), and it may be that the Spirodela O. does not represent the typical aquatic plant. But there are something there worth to follow, and it would be nice to be more certain about this.

 

[Malawi]

Diana Walstad's book covers some stuff on nitrite uptake by plants also. Take a look at that if you have it.

I have just ordered the book today.
They seem to be a bit hard to find, so I ordered a couple extras to resell at my local club.

BTW: The link that bugzbugz refered to was written by Walstad, but is a bit unconclusive.

 

[Malawi]

For sure!
I wouldn't argue that plants cannot take up nitrite, but I will say that at some level it will become toxic, just as very high levels of ammonium and nitrtate can become toxic in plants. I'm sure its the case that it takes much less nitrite to lead to toxicity than nitrate or ammonium. Again, I'm basing most of this on terrestrial plant research and it gets kinda cloudy with submersed plants.

Seems like we are pretty much in tune.

I hope that cloud can be lifted.