| dc.description.abstract | Centrospermeae specieswere collected at different sites along gradient of altitudes and aridity. Climatic data were obtained from meteorological research stations. Kranz leaf syndrome, δ13C values and carbon dioxide compensation points were used to examine for C3 or C4 photosynthesis. Results show C4 photosynthesis is a trait of modern dicotyledonae species and is of multiple evolutionary origins. C4 species occur mainly in lowland habitats characterized by high temperature, low precipitation and high rates of evaporation. The areas were often associated with salinity and high δ13C values of the species. C4 dicots were further differentiated into biochemical types NAD-me type and NADP-me type. NAD–me dicot type tended towards drier region than NADP-me dicot type. NADP-me type preferred more moisture indexed habitats. With increasing aridity, the percent C4 dicot abundance in the flora also increased. Inverse relationship does exist between rainfall (precipitation) and C4 percent abundance distribution (r=-0.91, R2= 0.83) along altitudes. C3 species dominate moist and colder habitats, especially at higher altitudes. A few species C4 species occur at high altitudes (3000-4000m asl) namely Sagina gallica, Silene abyssinica and Melandrium nordiflorum. The transition zone between C3 and C4 dicot species is rather narrow between 1500 to 1700m and thus much lower than recorded for the monocots (2000-2200m asl). The general pattern of δ13C values distribution along the altitudinal gradient show that the values of-10.60 to-16.55,-17.75 to-18.87 and-18.89 to 32.4‰ corresponds to altitudinal ranges 0-1500, 1550-1700 and … | en_US |
