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Many aquatic macrophytes/plants are able to use bicarbonate, most all algae.
Hydrilla does so indirectly, Potamogeton, Egeria, Myriophyllum etc a literature search and little searches on the APD, the Krib et al would give you an idea.
When you consider the use and the plants impact on the HCO3, all plants/algae will first use CO2, then when it gets below a critical level(different for most plants within a range, each plant has its own CO2 demand) and a light level(light drives CO2 demand). You can factor temp in here also.
Hydrilla can use free carbon dioxide from surrounding water when it is available and can switch to bicarbonate utilization when conditions favors its use i.e., high pH and high carbonate concentration(or KH) (Salvucci and Bowes 1983). These conditions occur in highly productive waters during warm water and high photosynthesis conditions. Under these conditions, hydrilla can also switch to C4-like carbon metabolism, characterized by low photorespiration, and inorganic carbon fixed into malate and aspartate (Holaday and Bowes 1980). This is called indirect bicarb use.
Most algae do it directly(on cell surface) or internally: http://md1.csa.com/partners/viewrecord.php?requester=gs&collection=ENV&recid=2043085&q=algae+carbonic++cell+surface&uid=787140842&setcookie=yes
A few such as Chara will do it like Hydrilla away from the plant but very close.
By pumping out H+'s they reduce the HCO3 to CO2. This causes the pH to go up very high( HCO3 > CO2(removed by plant) + leaving OH- left) and CaCO3/MgCO3(marls) are deposited. Many algae from their forms, patterns, structure through this deposition
See pages 8-9, and the refs for more.
Another easily accessible we ref:
Another on gas versus liquid resistence of the boundary layer differences.
Fairly interesting..............also the resistences of bicarb and CO2...........and liquid vs gas resistence.........
Another study comparing a non Bicarb user vs a bicarb user.
Another interesting paper from the Army Core:
That should keep you busy.
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