Andrew wrote:
Potassium is not integrated into the plant strucure to any great
extent. Potassium is predominantly involved in ion channels. It
regulates potential across the cell membrane, providing energy for
cellular processes, maintaining osmotic pressure, etc. Take away
potassium and the cell's biological processes shut down. FWIW plants
actually have quite a high potassium demand, second only to nitrogen.
Andrew

Define integrated. Remove a plant stalk, and you remove quite a bit of
potassium from the closed tank system. While potassium is mostly
cytosolic and not bound to protein, it is still intracellular (remember,
high Na+ outside, high K+ inside). That means it is sequestered from
the tank water and there is net uptake as plants grow. I believe that
is Philippe's essential question, since he is confused about the
accumulating potassium in his aquarium.

As for which nutrients leave a dead plant first, my best guess
(for the reasons stated above) is K, followed by N and P. As a general
rule, it is preferable to remove dead plant matter from an aquarium
rather than leave it to rot.

--
Elaine T __
http://eethomp.com/fish.html '__
rec.aquaria.* FAQ http://faq.thekrib.com