Re: Plants competing with algae

George Booth <booth at hpmtlgb1_lvld.hp.com> writes:

>I think all of us at one time or another have stated that it's good to
>densely plant because "plants outcompete algae for nutrients".
>I've always felt uncomfortable about this.  Does anybody know the
>basis of this statement?  Can plants use nutrients faster, thus
>removing them from the water before algae can use them?  This seems a
>little far fetched.  Nutrients should be evenly distributed in the
>water column, easily usable by anything nearby.  
>I prefer the "allelochemcal" reasoning for dense planting.

In tanks without complete circulation of the water through the substrate,
the amount of nutrients in the water column can be controlled. For example,
iron, manganese or even nitrates can be kept to minimum levels above the
substrate, while they are still available to the plants below from detritus,
soil, even laterite. The algae don't have roots! :-)   Once algae are
deprived of some needed nutrient(s) they will die.

Another theory is that fast growing and a densely planted tank will deplete
the water of nitrates.  The plants may be more efficient at removing ammonia
(i.e. nitrogen) from the water than the algae. Of course this does not apply
to a tank with an efficient biofilter, like a wet-dry.

Finally, and perhaps most importantly, the higher plants can obtain
macronutrients (incl. N, P, K) from their food reserve by recycling
nutrients from the older leaves to the newer ones.  This is how the plants
can survive an "initial starve the algae period." and other short periods
with low water nutrient concentrations. Starve the algae, and the plants
will feed themselves!  Once the algae are essentially eliminated, it is much
more difficult for them to establish a foothold.

Allelochemicals are another possibility!


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