Re: algae inhibition and RUBISCO>

[Thomas Barr <tcbiii at earthlink_net>]

> Subject: algae inhibition and RUBISCO
 
> I seem to recall a thread on the list about whether oxygen in the plant tank
> retards plant growth due to competing oxygenase activity. i don't know if any
> definitive conclusions were reached but it seemed the opinion was that this
> wasn't terribly significant.

It can certainly be significant. Up to 20-40% reduction in growth rates.
In our tanks? Perhaps some.
By all accounts, it seems to do more damage to most algae than to higher
plants. I have not seen much done to the plants and if it reduces the growth
when they have already produced well in excess of saturation, then slowing
them down is fine with me.

> it seems to me that is should be significant
> since plants are willing to go to great lengths to avoid this activity (c-4
> and CAM) and a pearling tank is obviously a very oxygen enriched environment.
> anyway, the question i'm getting around to asking is whether oxygen inhibition
> of photosynthesis could be the big algae buster in a healthy plant tank if
> plants are better adapted to deal with it than algae.

There are algae that are adapted to deal with it, Chara is one and green
spot algae is another (Both possess peroxisomes), there are others.

> it would be easy to test
> this theory so i suspect it's already been done - anyone know?
> elie

Generally......a high DO level(90-150%)is a good measure of plant production
and/or algal production. It's hard to get the O2 too high in our tanks to
cause toxic effects for fish and plants using plants. O2 degasses like CO2.
I've gotten to 150% but never saw much in the way of any problems associated
with high levels, except hacking plants back. If it self limits the plants
when it gets to 130% or more, great, dang weeds need to slow down the growth
anyway.
I've measured DO's of 300%+ is some waters loaded with nutrients. Not good.

The effects on bacteria should also be considered when talking about high DO
levels. There are certainly many interactions between algae, plant AND
bacteria in nutrient and other cycles within a tank/nature.

CAM metabolism is much more a method for dealing with dry xeric conditions,
eg Cacti, Yucca etc. I would say that it's inclusion  into the aquatic realm
is coincidental/incidental.
Isoetes is the only plant we keep that can does this and most of the
definitive work was done on a CA vernal pool plant which lives through both
desert like and wetland type conditions.
It is slow growing like all CAM plants. It also gets about 60% or more of
it's total CO2 intake from the substrate, not the water column, so the CAM
part while interesting, is not the only method even with this plant. This
plant is weird anyway so it's somewhat of an exception in a number of areas.

C4 and bicarb usage is another story. Endangered Orcutt grass uses C4(as do
a number of grasses) in the very same vernal pools and there are lots of C3
plants. There are some advantages/disadvantages to each method. Vernal pools
are extremely harsh environments for plants not adapted to the conditions
which are at opposite extremes. They are more desert like than aquatic in
most respects.

Some algae also have interesting CO2 and effective concentrating methods
also. But algae are typically never Carbon limited unlike many/most of the
plants we like.
 
Regards, 
Tom Barr