C₄ Photosynthesis at Barro Colorado Island, Panama

C4 photosynthesis is one of three metabolic pathways found in the photosynthetic tissues of vascular plants for assimilation of atmospheric carbon dioxide (CO2). Like crassulacean acid metabolism (CAM) photosynthesis, C4 photosynthesis has evolved from the ancestral C3 pathway. C4 photosynthesis is an adaptation that enhances CO2 assimilation in warm, high-light environments. On Barro Colorado Island (BCI), C4 photosynthesis (including variations of it) occurs in close to 60 herbaceous species from six families: Hydrocharitaceae, Cyperaceae, Poaceae, Euphorbiaceae, Amaranthaceae, and Portulacaceae. Plants are typically found in clearings and not inside the forest, and about one-third of the C4 species are non-native. With at least 42 C4 species, Poaceae is the greatest contributor to the C4 flora of BCI. One grass species, Homolepis aturensis (Kunth) Chase has C3–C4 intermediate characteristics termed C2 photosynthesis. Portulaca oleracea L. (Portulacaceae) is a C4 plant with the remarkable capacity to also exhibit CAM photosynthesis under conditions of water-deficit stress. Hydrilla verticillata (L.f.) Royle (Hydrocharitaceae) is a submerged species that lacks Kranz-anatomy typical of fully developed C4. The species usually exhibits C3 photosynthesis but induces a C4 CO2 concentrating pathway when CO2 concentration in the water declines.