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.