Plant preference.

[Cuffcairns]

It seems that most of what I read says plants want nitrates.
I also read , that plants actuly scavenge nitrate and convert back to other forms before they use it.
If the assumption that nitrate is what they want, then this would cause people to over biologically filter their water?
Just wondering what the general consensis is on this topic.

[Nicole]

what do you mean OVER biologically filter the water?

[Cuffcairns]

If it was the case that plants prefer ammonia to utilise than nitrate, then wouldn't using bacteria to convert everything to nitrate slow down your plant growth. I.e. over filtrate.

[Yabbies4me]

If it was the case that plants prefer ammonia to utilise than nitrate

That's not the case.

This, or similar questions, have come up a few times here recently... and as Rupe has stated each time, the plants will use Amm when young seedlings, after that their preference is for Nitrates.

The bit about plants converting Nitrates back to other forms... did you read that on here?... what did it say they were converting it back to?

...and if you don't "biologically filter" the water sufficiently you will get Amm and N02 build up... that will kill the fish.

Cheers.
.

[Nicole]

The degree to which ammonia forms the ammonium ion depends on the pH of the solution. If the pH is low, the equilibrium shifts to the right: more ammonia molecules are converted into ammonium ions. If the pH is high (the concentration of hydronium ions is low), the equilibrium shifts to the left: the hydroxide ion abstracts a proton from the ammonium ion, generating ammonia.
This is because as pH drops, there is more free hydrogen (H+) in the water, thus the ammonia (NH3) picks up an extra H+ ion to form ammonium (NH4+). Conversely, as the pH rises to the alkaline area, the free H+ bonds with an oxygen atom to become hydroxyl molecules (OH-). This means the extra H+ in ammonium gets pulled away by the oxygen atom, which forms OH- and NH3.

if pH<7, NH3 + H+ = NH4+
if pH>7, NH4+ = NH3 + OH

There is no definitive evidence that plants take up NH3 directly. Rather, since NH3 has no charge, it can diffuse right through the plant cells while NH4+ cannot. But once the NH3 gets into the plant cells, it usually finds a free H+ atom and becomes NH4+ that the plant can then use and store.

If you really want to get scientific about it, yes, eventually the NH4+ molecule gets broken down into its single atomic components for use by the plants. The only reason that plants take up NH4+ or NH3 rather than just N2 by itself is because they are much more readily available to plants than atomic nitrogen.

And yes, NH3 can actually be toxic to plants at high levels. At low levels, it is taken up as normal, but it can inhibit growth or completely kill plants at high levels, but these levels are almost impossible to reach in normal aquariums. The fish would die and you'd notice a terrible smell from the water long before you noticed any problems with the plants.

Hope I didnt rant too much....