Re: NH4+ vs. NO3-
On Wed, 9 Aug 1995 Aquatic-Plants-Owner at actwin_com wrote:
> From: Nick LaRocca <nickl at css_sed.monmouth.army.mil>
> Date: Wed, 9 Aug 95 15:16:16 EDT
> Subject: Re: Aquatic Plants Digest V1 #233
> Hello Steve:
> The chloramine test is a bit pricey. However, a phone call to your water
> utility chemistry department will quickly confirm whether chloramine is
> being used.
> As I said, neither plants nor fish will handle free ammonia(NH3). Some (not all)
> plants will utilize the ionized form (ammonium=NH4+). Fish do not tolerate
> ammonium either, however.
Free ammonia rapidly ionizes to NH4+ in tanks with neutral or acidic pH,
I don't have the tables handy but I beleive most is present as NH4+ at pH
below 8 which is where most planted tanks are. Certainly NH3 or NH4+ are
toxic to all animal species at very low concentrations. However plants
contain enzymes which allow them to attach NH4+ ions to carbon
'skeletons' to make amino acids. Plants also contain enzymes to reduce
NO3- to NO2- and then to NH4+, but this is a very energy expensive
process so in the presence of NH4+ the nitrate reduction pathway is shut
down. The point here is that plants must get nitrogen in the form of
NH4+ before they can use it. (Info from Salisbury and Ross, Plant
Physiology, which is heavily biased toward terrestrials so if there are
changes for aquatic plants please correct me).
Somewhere I remember
reading that some aquatic plants (crypts) are not effecient at reducing
NO3-; in high nitrate waters they accumutlate this compound--I have also
heard that this type of accumulation can lead to crypt 'melt down'.
This is one of the reasons that I suspect in plant tanks with a HIGH plant
to fish ratio, excessive bacterial filtration is not only unnecessary but
may actually be detrimental to the plants. Certainly ammonium levels can
be attained that are toxic to the plants but by then most of the fish
will be dead...