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[APD] RE: plant/algae competition

> Oxygen can be very toxic for all living things.

Depends on the concentration.

> It readily breaks down to form oxygen radicals which are very unstable
and damaging. To deal with this, we have two enzymes, superoxide dismutase
(SOD) and
 >peroxidase which quickly breakdown the radicals into water (via
peroxide). We have these enzymes, plants have these enzymes and I expect
that algae would have 
>these enzymes also.

Some algae do, some do not. Only a very few have Peroxisomes(two groups
only) but more have peroxisome type pathways to deal with high levels of O2.
Others have ways to concentrate CO2 so as not to have wasteful respiration
occuring even at high O2 levels. Some have both. 

> However, the efficiency of these enzymes can vary from species-to-species
depending on environmental conditions. I know of certain bacteria that are
inhibited by 
>high dissolved oxygen levels. Perhaps this is the case for algae as well?

Yes, but many of the algae that are the worse, often do okay, well even at
very high O2 levels, like some blue greens, Cladophora, green spot etc all
do great at very high levels of O2(125-200% beyond saturation).

> This could be tested by setting up a tank with light/nutrients/CO2 and no
plants (perhaps plastic plants) and monitoring and controlling DOT levels
by injecting pure oxygen gas. Might be an interesting experiment for anyone
with the right equipment who is so inclined.

I already did this last year.
I did a study and evelevated the O2 to 15ppm using a YSI monitor and the
pH/KH for CO2 at 25ppm.
Lighting, 4100K and 6500K at 350uEinsteins.

4 tested tanks:

High O2
High CO2
High O2/CO2
This is for algae culture only(no plants) and there is no substrate except
for glass and equipment surfaces:
2 Types of substrates were used for quantification: plastic val leaves and
glass slides.
Glass accumulated more CHL a per unuit area than the plastic leaves.
10ppm NO3: 1ppm of PO4, trace added at 1ml of SeaChem Flourish to 15 liters
of water(tap, GH 5 KH 3) : duration 3 weeks 
4 systems were investigated:
The levels of CHL a were slightly higher(22%) in the CO2 rich medium than
the control
 "          "         "        "          "     significantly higher(51%)
in the CO2/O2 additions than the control    
"          "          "         "         "     slightly higher in the O2
"           "          "        "         "     lowest in the control.
Essentially from these results:
Algae species composition changed with higher/lower gas concentrations, but
overall the levels of CHL a remained somewhat constant.
Some species of algae are adapted to dealing with high O2 environments,
such as green spot, some Cladophora, some BGA's, several other encrusting
species(similar to green spot).
Many of the more common nusiance species that occur in well run tanks
appeared in the high CO and O2/CO2 tanks.
The control had more common species found in ponds etc. Herbivores where
screened using a filter. 
I'm not done with this study yet, but it's not the answer folks are looking
for I suspect.

You can look in the past APD archives for more about it and

Tom Barr

> Clint Brearley
> Melbourne, Australia

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