Photosynthetic light response in three carnivorous plant species: Drosera rotundifolia, D. capensis and Sarracenia leucophylla

Photosynthetic properties of carnivorous plants have not been well characterized and the extent to which photosynthesis contributes to carbon gain in most carnivorous plants is also largely unknown. We investigated the photosynthetic light response in three carnivorous plant species, Drosera rotundifolia L. (sundew; circumpolar and native to northern British Columbia, Canada), Sarracenia leucophylla Rafin. ('pitcher-plant'; S.E. United States), and D. capensis L. (sundew; Cape Peninsula, South Africa), using portable gas-exchange systems to explore the capacity for photosynthetic carbon gain in carnivorous plant species. Maximal photosynthetic rates (1.32-2.22 mu mol m(-2) s(-1) on a leaf area basis) and saturating light intensities (100 to 200 mu mol PAR m(-2) s(-1)) were both low in all species and comparable to shade plants. Field or greenhouse-grown D. rotundifolia had the highest rates of photosynthesis among the three species examined. Dark respiration, ranging from -1.44 (S. leucophylla) to -3.32 (D. rotundifolia) mu mol m(-2) s(-1) was high in comparison to photosynthesis in the species examined. Across greenhouse-grown plants, photosynthetic light compensation points scaled with light-saturated photosynthetic rates. An analysis of gas-exchange and growth data for greenhouse-grown D. capensis plants suggests that photosynthesis can account for all plant carbon gain in this species.