Re: ammoniUM, nitrate, phosphate, algae, plants...

Gerard van Klaveren writes:

"Is it possible the aq. plants do prefer ammoniUM and algae 
 do prefer nitrate or even phosphate?

 Or do algae also prefer ammoniUM above nitrates or even phosphates?

If the first is right, it should be easier to keep the algae out of 
the aquarium.

Can someone refine this part of the subject?"

Algae do prefer ammonium to nitrate, just like aquatic plants. This is 
because the nitrogen is in a reduced state which the algae can 
directly utilize for the production of amino acids (the building blocks 
of proteins). Nitrate must first be reduced to nitrite and then 
ammonium in order for the algae and plants to utilize nitrogen in this 
state. This takes energy and, as a result, the plants and algae cannot 
grow with equal efficiencies given the same amount of nitrate 
nitrogen as they would on ammonium nitrogen.

There are many factors which are important in determining 
competition between plants and algae (ie. light, nutrient availability, 
temperature, CO2 concentration). It is not enough simply to consider 
the redox state (nitrate, nitrite, or ammonium) of the nitrogen in your 
plant tank. I think the ideal situation to achieve is one in which there 
is a very high rate of turnover of nitrogen in the system so that the 
algae never get a chance to flourish. Under these conditions nitrogen 
concentrations may be undetectable, but this does not mean the plants 
are nitrogen limited.

Phosphates are something completely different from nitrates. The 
only form of phosphate aquatic plants and algae can use is PO4-. This 
is unlike nitrogen which can exist in many states the plants and algae 
can utilize. This is one reason (definitely not the only reason) some 
scientists believe phosphate is the true limiting nutrient in 
freshwater (and some marine) aquatic ecosystems, not nitrate. 
Anyway, the main source of phosphates to the plant tank come from 
organic sources such as fish food and fish feces. Plants and algae also 
have the ability to store phosphate in their cells as polyphosphates. 
This is another difference which separates nitrogen and phosphate. 
Even if concentrations are undetectable in the water, the plants and 
algae may have plently of phosphates in reserve to use for growth. 
Well, I hope this helps.

Robb D. VanPutte
Dept. of Biology
Texas A&M University