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Re: Nitrite (NO2) as a plant nutrient?

Ali ("spiny eel" - come on Ali, use your REAL name on the APD, especially if
you want people to take you seriously) asked the other day about Nitrite
(NO2) as a possible plant nutrient. One of his friends has advised him that
plants only use Nitrate (NO3). Kenny Poh answered his question, sort of...
unfortunately the answer is partially incorrect...

> NO2 is the intermediate product of the nitrogen cycle. So, if is present
> abundant amount, something is really wrong with the nitrogen cycle: either
> water is not 'matured' or there's excessive amountof waste in there.

The above is correct, as far as it goes...

> There're commercially available capsules of these bacteria around to
> the nitrogen cycle. However, I caution against its rampant use. The idea
is to
> acheive equilibrium between waste production and the nitrifying bacteria,
> overdosage or under dosage of these bacteria is definitely harmful.

While there ARE several commercial preparations that CLAIM to contain the
proper bacteria, at this point in time even the very identy of the bacteria
responsible for the conversion of ammonia/ammonium into nitrate in fresh
water ecosystems is uncertain. So whether thse commercial preparations can
do what they claim to is open to doubt. The second part of Kenny's answer,
that "overdosage or underdosage of these bacteria is definately harmful", is
pure speculation on Kenny's part.

A system can definately have TOO FEW nitrifying bacteria present for the
bioload (a new tank with a lot of fish for example). That can definately be
harmful to the animals, due to ammonia toxicity. But a system cannot support
more nitrifying bacteria that there is food to feed them - the excess will
simply die. Unless someone added a HUGE overdose of one of the commercial
preparations that DID contain live bacteria (most of them do not have live
nitrifying bacteria in them), I doubt that the added bioload of a few dying
bacteria is going to swing things one way or another.

The best solution for the initiation of the nitrogen cycle in ANY tank is
patience and restraint. Not too many fish at first and be patient until the
natural nitrifying bacterial population builds up to a sufficient level to
handle the excretia from the fish. The big problem is that while most
bacteria can multiply exponentially at astonishing speeds, the division rate
for most bacteria capable of nitrification is measured in hours (usually 24)
not minutes. So it takes time (measured in days and weeks) for the bacterial
population to build up sufficient numbers to handle regular inputs of
ammonia (fish waste). As the bioload increases, so will the bacterial
population, but there will always be a time lag between the two.

For the impatient, the best choice is to use a pre-cultured foam filter
which has been in an established aquarium for a period of several weeks. It
will have a built in bacterial population.

> And yes, plants make use of nitrate only.

Sorry Kenny, this is simply not true. Aquatic plants are capable of
assimilating nitrate (NO3), nitrite (NO2) and ammonium (NH4) as inorganic
sources of Nitrogen. In most aquatic ecosystems, nitrate, which is the most
thermodynamically stable and highly oxidized of the three species, is the
predominant form of fixed nitrogen present (predominant does not imply that
it is the preferred or most readily available form of nitrogen for plants).

Most aquatic plants would prefer to use ammonium (NH4) directly, as it
requires no, or very little energy expenditure on the part of the plant to
get the ion inside of the cell membrane and be used, but through the use of
two separate enzymes, nitrite reductase and nitrate reductase, both nitrate
and nitrite are useable by plants as sources of nitrogen.

James Purchase