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Re: Nutrient limitation


>From: eworobe at cc_UManitoba.CA
>
>IMHO, the easiest to use as a limiting nutrient is phosphorus. It is used 
>in relatively large amounts by plants and can easily be omitted from 
>water-based plant fertilizers. Having said that, its important to 
>understand that macrophytes can in no way outcompete algae for P. Algal 
>uptake kinetics are such that they can drive the P levels far lower than 
>macrophytes can... after discussing this with Sears and Conlin and 
>thinking about it for a few months I came to the conclusion that the 
>algae become P limited because the TURNOVER rate of P in algae is much 
>higher than in macrophytes. As the P becomes available (through algal 
>senescence) the macrophytes 
>sequester just a small amount but keep it much longer so that over time 
>the algae eventually lose out. This is at present not supported by any 
>research that I know of.

I would support this based on my experimental results.  In an
algae-infested tank with algae-eating fish such as platies, the algae
eventually loses and the tank becomes spotlessly clean.

One caveat:  Once the tank is clean, the plants themselves become limited
and soon you'll find that one or more species don't make it.  In my tank,
the Anubias and Hygrophila polysperma began to melt while the other plants
just kept growing (right before the cyanobacteria plague).

--
David W. Webb           Texas Instruments
(972) 575-3443 (voice)  http://www.dallas.net/~dwebb
(214) 581-2380 (pager)  2145812380 at alphapage_airtouch.com