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Re: what you read
Anthony Ciarochi wrote:
[snip]
> The parts I found particularly amazing are followed by a (!).
>
> 1. Both Echinodorus and Cryptocoryne are marsh plants, not true aquatics (!).
> Being marsh plants, they are unable to absorb nitrogen through their leaves, and
> must be fertilized at the root (!).
Most members of both families grow emersed for much of their life in
their natural habitat. For Echinodorus in particular a lot of them will
grow emersed in aquaria unless you have a really big tank.
I don't think that's an indication that they must be fed by root. Purely
terrestrial garden crops can be fertilized with foliar feeding.
> 2. Aquatic plants are only able to absorb nitrogen in the form of ammonium, and
> are unable to metabolize either nitrite OR NITRATE (!). The book goes on to
> state that utilization of nitrate is ONLY characteristic of terrestrial plant
> life. It doesn't say anything about a plant's ability to metabolize ammonia
> (vs. ammonium), other than saying to keep pH under 7.0 so that you never have
> any.
What I've read is that aquatic plants will use ammonia first if its
available and ignore nitrite/nitrate as long as sufficient ammonia is
available. I've also read that terrestrial plants work in reverse, taking
in nitrate by preference over ammonia. I don't think the difference
between ammonia and ammonium is significant.
>
> 3. If nitrate builds up in the water, it will actually stunt plant growth unless
> also accompanied by increased levels of light (!). As a result, plants which
> are growing vigorously under low to moderate light may suddenly stop all growth,
> despite the addition of trace elements, etc.
The "toxicity" of nitrate is probably disputable, but plants certainly
would need more energy to metabolize nitrate than they need to metabolize
ammonia. The need for more energy could mean a need for more light.
Roger Miller