Photosynthetic characteristics of the aquatic carnivorous plant Aldrovanda vesiculosa

Aldrovanda vesiculosa L. (Droseraceae) is a critically endangered aquatic carnivorous plant. It is considered to be strictly stenotopic. Chemical and physical factors were measured in situ in A. vesiculosa stands at eight sites. The O-2 concentration usually ranged between 0.25-0.28 mM. There was a wide range of pH of 5.04-7.60, but with a median of 7.17. Total alkalinity ranged between 0.16-4.2 meq l(-1) but was mostly within 1.0-2.7 meq l(-1). A high CO2 concentration was found in all stands; it ranged between 0.14-3.5 mM and was usually within 0.2-0.5 mM. A high CO2 concentration appeared to be the most important condition for rapid apical growth. It appeared to be a strict CO2 user with a CO2 compensation point of 5.9-8.2 mu M, a K-m of 165 +/- 77 mu M CO2, and a maximum photosynthetic rate of 99 +/- 10 mmol kg(-1) (FW) h(-1). It was found to be photophilous and exhibited a light compensation point of 6.0 W m(-2). A. vesiculosa grew in unshaded, and also shaded stands with only 18-24% of incident irradiance at the water surface. Photosynthetic rates rose from 15 to 34 degrees C. The highest photosynthetic rate was found in young apical shoot segments and it declined toward the bases. (C) 1997 Elsevier Science B.V.