Long, long ago (might find a reference* if pressed) used
Wolfia arrihiza
http://webcenter.ru/~duckweed/wolfia-e.htm
with a pH meter, following change in pH associated with uptake of CO2 from
a dilute bicarbonate solution. Lovely little (higher) plant if you can get
hold of it.
Regards
David
http://www.oxygraphics.co.uk/
* Reference maybe WALKER DA 1973 Photosynthetic induction phenomena and the
light activation of ribulose diphosphate carboxylase. New Phytol 72: 209-
235
or even WALKER DA 1976 CO2 fixation by intact chloroplasts: photosynthetic
induction and its relation to transport phenomena and control
mechanisms. In J Barber ed, The Intact Chloroplast, Chapter 7,
Elsevier, Amsterdam pp 235-278
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