[APD] Re: # Re: Gw/NH4

[Paul Krombholz <krombhol at teclink_net>]

I looked at a variety of aquatic plants (Vallisneria, Elodea, 
Ceratophyllum, Zosterella) and found that they could store enough 
excess phosphate in their tissues so that they could quadruple their 
mass using just the stored phosphorus before their tissue content 
became low enough to limit the growth rate.  They could store enough 
excess nitrogen so that they could at least double their mass using 
just the stored nitrogen before the tissue nitrogen fell to a low 
enough level to limit the growth rate.  So I find it a little strange 
that Tom is saying that aquarium plants stop growing in just a few 
days after the nitrogen content of the water falls below levels 
measurable with test kits.  and the same thing if phosphorus falls 
below measurable levels.  I would think that if either N or P were 
kept at measurable levels for a week or so, the plants would be able 
to stock up and get their tissue contents up near their maximum 
possible values.

 The only way to resolve this issue would be to harvest aquarium 
plants and do nitrogen and phosphorus analyses.  For example, keep 
the nitrate content of the water at around 5 ppm for about a week, 
then harvest, dry, and do a Kjeldahl nitrogen analysis.  For the 
plants I worked with, 1.5% N was the critical value below which 
growth was reduced.  Luxury consumption of N got up to a little over 
4.0%.  For phosphorus, the critical value was 0.15% and luxury 
consumption went up to around 0.65% to 0.7%
--
Paul Krombholz in sunny, cool central Mississippi
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