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.