[APD] RE: algae/plant competition and uptake rates

["Thomas Barr" <tcbiii at earthlink_net>]

>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...)

Here's a graph to illustrate:
 
http://www.picturetrail.com/gallery/view?p=999&gid=2810752&uid=1473668&membe
rs=1

>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.) 

I'd initially say for the sake of arguement they would take up more in the
planted tank due to leeching of nutrients from the plants, plus all the
available surface area that the plants provide for attachment. But we do
not see that.

>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?

I'm suggesting, as I have for some time, that algae "know" when something
else is growing and if the system is stable.
You see this with green water and a few other species with algae<=> algae
interactions.
When algae decide to bloom can be subtle as far as the reasons and not well
studied in ecosystems.

There is a large periphyton study that's going to be conducted in the
Everglades coming up.
It is one of the only periphyton dominated ecosystems in the world. Roughly
40-50% of the production is from periphtyon.

Now why don't green water take over also in these systems?

If you remove the plants you will see this occur.
Things are not quite as simple as we would like them to be overall here and
in natural lakes.
But we have more control in many cases with our little glass boxes.

>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?

Well why would epiphytic algae outcompete the much smaller phytoplankton?
Same reason.
There's plenty of nutrients for phytoplankton in our tanks but it's quite
rare.
It also likes very high light(going back to that better usage of light).  

But the light issue plays to the phytoplankton's advantage, unless it's a
floating mat of epiphytic algae etc.
Some algae seem to know when to grow and when not to. I'm sticking with
that for now, Allelopathy just I don't buy.

Try adding carbon if you'd like to rule that one out.
I already know the answer for that. 

>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?

Not IMO. 
But we scape the algae from the glass, the rocks, prune the older plant
parts that get algae, we add algae herbivores. 
There may be something to be said for allelopathic algae compounds, at
least with Green water, perhaps others, what is prevent other algae from
taking over when algae is on the march?
Folks talk of plant compounds, well there are algae compounds that can do a
number of many things in aquatic environments, I'd argue the algae have the
advantage there. 

>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?

Well there is certainly less light hitting the verticle surface on the
sides vs the center where the plants are.
Rocks can see the same pattern, the tops get crusty, the side remain
relatively clean.

If you have enough light/nutrients/water, something is going to grow.
  
There are several things going on, I also am doing a study on nitrogen
uptake by epiphytic/filamentous algae vs Sag kurziana, a common plant in
the springs of Florida.
Hopefully I'll be able to determine the rates better in a community setting
and also talk about nitrogen in terms of the spring ecosystems. 

You raised good points Jim. I do not have all the answers, I may never even
come close, but I have some good hunches to work on still.Things I can rule
out.  
Bacterial interactions may play a role. Indirectly or directly. Dissolved
O2 levels may also play some role also with bacteria, it might inhibit SOME
species of algae from attachment to some surfaces, but not all species.
Root conditions and O2 transport to the substrate is also something few
folks here consider. This effects the bacteria there.But using carbon
removes these allelopathic issues.
So I'm back to the alkgae know when things are stable and unless they have
committed to making a go of it, they wait till things change for the worse.

Regards, 
Tom Barr


- Jim



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