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I've been looking up a number of studies on the air lacunae in aquatic plants. Many store their O2 in these air chambers during the day and as the levels of O2 build the amounts of PR are correlated inversely to the O2 level within these lacunae. Nothing new really. 

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. 

Lots of O2 would mean more hetrotrophic bacterial growth perhaps or better fugnal decomposition of detritus(most all Fungi are aerobes). 

Some species of algae have very good carbon concentrating mechanisms CCM's,(and some plants) using HCO3 which removes the idea of low CO2 around the Ruisco enzyme and are able to remove the O2 oxygenase substrate competition. 

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.

But what happenes when we add high levels of CO2 so that the CCM do not need to operate(suppose the genes for the CCM are not trascribed since CO2 is now non limiting)and instead they end up Photorespiring?

Some algae fit this description. 
What has not been done nearly as much as looking at the effects of both high CO2 and O2 together.

I need to stress the notion that each species of plant and algae need to be viewed case by case. Some may fool what you except to see, but I do hope to find some generalization regarding this.

I think many of the algae that bug us when we have poor CO2 and O2 levels are suspectible to this but Green spot and Green water and certainly some of the Cladophora species fall into more like the higher plant groups. 

Well it's fun torturing algae anyway. Better than the other way around eh?   

Tom Barr