Aquatic CAM Photosynthesis

Abstract

CAM photosynthesis in an aquatic plant was first suggested by the observation of marked diel (24h) changes in malic acid in photosynthetic tissues, but not in nonphotosynthetic tissues, of Isoetes howellii (Lycophyta: Isoetaceae) (Keeley 1981). At the time everyone "knew" that CAM was an adaptation for increasing water-use efficiency in xeric adapted plants, and thus there was some reluctance to accepting the notion of an aquatic CAM plant. Phrases such as "CAM-like" or "aquatic acid metabolism (AAM)" were coined to avoid this apparent paradox (Cockburn 1983).