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Re: Photorespiration

Tom Barr wrote:
> But how this O2 and PR effects the algae/bacterial 
>epiphytes may be far more interesting since this is most 
>often what is eaten in nature by the herbivores like snails. 

"Why is it interesting that snails eat algae/epiphytes regarding
the O2 och PR effects? Are the algae/epiphytes getting
easier to digest/scrape off when PR:ing?"

Well, the snails are the consumers here, they are not eating the
plants, actually few herbivores actually eat the macrophytes,
they generally just eat the algae on the plants.

The plants act as structure/surface for periphyton generally.
How the bacteria and algae respond to the plant's output of O2
is something that has not been looked at much(if at all).

The periphyton that grows on the macrophytes is like a tiny
forest ecosystem in itself.

Much more complex than perhaps many people think. The littoral
system where macrophytes grow is a very complicated place. 

The pelagic water column phytoplankton are well studied and much
better understood. 

> This effectively reduces virtually all PR. So even if the 
>O2 levels are high, depending on if the plant/algae 
>possess a good means to concentrate the CO2 around 
>the the enzyme responsible for roughly 40-50% of 
>the dry weight mass of the plant/algae has little effect.

"Concentrate CO2 around the.. what?"

RUBISCO, the enzyme that fixes carbon. If there's lots of CO2
around this important enzyme, then it will work great. If
there's lots of O2 then it will fix the O2 instead(and add no
carbon=> hence no glucose/triose sugars). If the enzyme is busy
losing carbon from trying to fix O2, it cannot fix CO2.
Therefore the amounts of each gas around this enzymne is
important and impacts its efficiency greatly.

The Carbon concentrating mechanism(CCM) will remove the effects
of low CO2 around the enzyme by adding so much CO2 around it
that the O2 doesn't effect the fixation of carbon significantly.
"What has little effect?"

High O2 levels.
"Why is the enzyme-percentage of the plant dry weight 
mass interesting?"

Well since this enzyme adds 40%+ of all the mass you see in the
plants you grow. 40+% of your plant is Carbon.

>O2 oxygenase substrate competition. 

"What is this? =)"

The enzyme will fix CO2 _or_ O2, hence also has oxygenase
activity which competes for the CO2 substrate.
Less O2 around it, it will work better, more then it will
greatly reduce it's efficiency.
C4 plants are not effected by high levels of O2 or lower levels
of CO2 for example(eg Hydrilla).

"Daniel Larsson"

Tom Barr

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