Photosynthetic characteristics of the aquatic carnivorous plant Aldrovanda vesiculosa

Abstract

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 1 −1 but was mostly within 1.0–2.7 meq 1 −1. A high CO 2 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 CO 2 concentration appeared to be the most important condition for rapid apical growth. It appeared to be a strict CO 2 user with a CO 2 compensation point of 5.9–8.2 μM, a K m of 165 ± 77 μM CO 2, 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°C. The highest photosynthetic rate was found in young apical shoot segments and it declined toward the bases.