Photosynthetic pathways, distribution, and ecological characteristics of grass species in egypt

This study is based both on our own results, especially δ¹³C analyses, and on data in the literature. Of the 225 species of Poaceae reported from Egypt, 105 species show the C₃ and 120 the C₄ type of photosynthetic CO₂ fixation. Winter annual and perennial grasses active in winter are mainly C₃ species, while summer annuals and the other perennials are mainly C₄ species. The percentage of C₃ species decreases with decreasing latitude. This seems to be mainly related to increasing temperatures. The C₃ grass species are found preferentially in the Mediterranean, Irano-Turanian, Mediterranean/Irano-Turanian, and Saharo-Arabian chorotypes, while the C₄ species are mainly found in the Sudanian, Saharo-Arabian/Sudanian and Tropical chorotypes. In Egypt, the NADP⁺-ME and NAD⁺-ME subtypes of C₄ photosynthesis are found in about equal numbers of C₄ species, while the PCK subtype is relatively rare.