[APD] RE: competition with algae

["Jim Seidman" <js5 at seidman_net>]

Tom -

I'm afraid I'm still not getting it. If you have sufficient patience, I'd
appreciate it if you'd try explaining it again, as I'd really like to
understand what you're staying. (I suspect many lurkers would too...)

>Nutrients, through enzyme kinetic values of uptake transportors.
>These follow Michaelis-Menten dynamics. 
>At some point, the smaller algae can no longer take up or store any more
>and max their growth rate, make more reserves etc no matter how much
>nutrients are present, the plants on the other hand, can take up more.

I think I understand the implication of Michaelis-Menten on uptake rates,
but I can't understand the relevance here. Sure, if a tank contains 10 ppm
NO3, the plants will take up more than the algae, at least looked at on a
per-unit of dry weight basis. However, won't the algae take up the same
amount of NO3 in a planted tank with 10 ppm NO3 and an unplanted tank with
10 ppm NO3? (NO3 is a completely arbitrary choice of ion here - substitute
PO4, Fe, K+, etc.) 

Perhaps it would help me understand if you answered this question: In a
eutrophic planted tank, is there anything that prevents algae from
achieving enough uptake for rapid growth?

>You are keeping them well supplied with nutrients and growing well. New
>growth, relative to light, is able to outpace the epiphytic algae, this
>allows less resistence to gas exchange/nutrient uptake/light for the plant
>leaf surfaces.

You framed this as a comment about epiphytic algae, and I can understand
the argument in that context. But in my experience healthy plant growth
inhibits algae on rocks, driftwood, glass, and everything else as well. If
this was the main factor, wouldn't we have beautiful plants that we'd be
unable to see through the algae-encrusted glass?

>If you ask the leading experts on aquatic plants they will generally say
>light.George Bowes, Limnologist, the folks at IFAS etc.

Looking at local Illinois lakes with their dense surface cover, I can
certainly believe light competition plays a role. However, does the
limnology argument apply in a tank with a large foreground, where there's
plenty of light hitting glass, wood, and other surfaces for sessile algae?

Stated differently: Assuming a foreground, I don't see how healthy growing
plants changes substantially the amount of light hitting the front glass.
Yet in my experience having the healthy plants makes a big difference in
the growth of algae on that glass. Why?

- Jim


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