Ecological evidence concerning the adaptive significance of the C4 dicarboxylic acid pathway of photosynthesis

Summary Ecological data were analyzed to determine the environmental conditions associated with the occurrence of plants possessing C₃ and C₄ photosynthetic pathways. Non-parametric analysis of variance, multiple regression analysis and discriminant analysis techniques were applied to information derived from separate studies on plant species in California and central Europe. All the analyses revealed significant differences in ecology between the C₃ and C₄ groups. The occurrence of C₄ species was greater where summer or winter temperatures were relatively high and moisture availability relatively low. Using discriminant analysis, more than 80% of the species considered were classified into the correct photosynthetic category on the basis of their distribution with respect to temperature. No significant differences between the C₃ and C₄ groups were found for other environmental factors, including light, soil nitrogen, soil salinity and continentality of climate. These results support the suggestion from previous physiological studies that C₄ species may possess competitive advantages under conditions of high temperature and intermittent water stress. The C₄ species were relatively restricted in the range of environmental conditions where they occurred, and as a group C₄ species may be ecologically more specialized than C₃ species.