Variable carbon isotope ratios of Dudleya species growing in natural environments.

Measurements are reported of carbon isotope ratios of Dudleya species growing in natural plant communities. Considerable variation in the δ13C values are interpreted as indicating substantial flexibility of the photosynthetic pathways between C3 and CAM. The variability in photosynthetic pathway was in response to genetic factors, stage of plant development, life-form, and environmental conditions. Species active during drought periods have less carbon isotope fractionation than species that are summer-dormant. Summer-active species from drier habitats have less negative δ13C values than those from more mesic sites. On the same plant, leaf tissue had more negative δ13C values than tissue from the inflorescence. The less negative carbon isotope ratios are indicative of an increased proportion of exogenous CO2 fixed in dark vs light. The ecological significance of these results is discussed.