A Preliminary Study of Crassulacean Acid Metabolism (CAM) in the Endangered Aquatic Quillwort Isoetes sinensis Palmer in China

<正> Isoetes sinensis Palmer (Isoetaceae) is an aquatic or amphibious plant that is critically endangered in China. Previous studies have revealed the crassulacean acid metabolism (CAM)-like photosynthetic pathway occurs commonly in submerged leaves in genus Isoetes. Water chemistry parameters and the titratable acidity content of the plant extract were measured from samples obtained in the early morning (7:00) and late afternoon (15:00) from two I. sinensis populations in China. One population occurs in the eulittoral zone of a freshwater tidal river at low elevation (134 m) and another occurs in a densely vegetated, high elevation (1 100 m) alpine shallow pool. Significant differences in pH and titratable acidity of the plant extract were detected between the morning and afternoon samples. These changes are associated with diurnal changes in water chemistry. Our results provide the first evidence for the existence of the CAM pathway in the East Asian endemic Isoetes sinensis Palmer. The magnitude of fluctu