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Re: deficiency casued by too much light ?

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Hugo Hoekstra wrote:

> After some pruning, I discovered (can you imagine what a jungle it is)
> another specimen of this Nomaphila which had been growing under a big floating
> Ceratopteris. The bottom leaves were missing but it looked so much better
> than it's counterparts which are growing directly under a tube. Not one leaf
> showing a deficiency, all bright green.  So could it be that the deficiency
> was caused by too much light ?

Yes and no, as near as I can tell.

The deficiency isn't technically caused by the light intensity - it's
caused because the plant can't obtain a nutrient (possibly potassium in
this case) fast enough to match it's growth rate.  In the case of
potassium, the plant can extract the nutrients needed for new growth from
the supply in its older leaves.  The result is that the older leaves show
the deficiency symptoms and die an early death.  I think you understand
that, I'm just repeating it now for the sake of being complete.

While the light doesn't cause the deficiency, reducing the light *can*
cure it.  Your second Nomaphila illustrates that.  It grew in a setting
where the availability of light rather than availability of the nutrient
was probably growth-limiting.  The plant could get enough of the normally
deficient nutrient to match the light-limited growth rate.  The result is
a healthy looking plant.

If your tank is very brightly lit, then you may be able to reduce the
lighting and avoid further problems with nutrient deficiencies without
losing any plants.  If your tank is only moderately lit, then you might
rather fertilize.

Recovery from the deficiency symptoms after reducing the light probably
won't be immediate.  I once transplanted a calcium-deficient sword plant
from a brightly lit tank to a more moderately lit tank.  The sword plant
put on two or three more deformed leaves after it was transplanted, then
started to produce normal leaves.


Roger Miller