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Re: Aquatic Plants Digest V3 #52

Alternanthera; This genus does contain plants which are aquatic. You may, 
or may not, have an aquatic plant. Most likely, the plants grow as 
emergents in nature and can grow either as aquatics or terrestrial plants.

Nighttime CO2 uptake; There are three processes at work. The first is 
uptake of CO2 into the plant. This may, or may not occur at night but the 
internal CO2 concentration within the aerenchyma certainly increases due 
to respiration and trapping of CO2. Aquatic plants are adept at recycling 
respired CO2. The second process is the assimilation of CO2 onto C3 or 
C4 acids. This is energy dependent and does not occur in the dark except 
for, as has been mentioned, CAM plants. Interestingly, there ARE aquatic 
CAM plants... most notably in the genus Isoetes. In these plants CAM is 
not a response to drought as it is in terrestrial plants, but is a 
response to SEVERE carbon limitation. During the day, the CO2 
concentration in the water reaches 0 so the plants take in CO2 and 
assimilate it into C4 acids at night. The third process is the reduction 
of CO2 as ably described by Mark. This process does not occur in the 
dark, not even for CAM plants.