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[APD] Re: # Re: Gw/NH4

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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