ECOPHYSIOLOGICAL COMPORTMENT OF THE TROPICAL C3 CAM-INTERMEDIATE TREECLUSIA-ROSEA IN THE FIELD AS ASSESSED BY ANALYSES OF STABLE CARBON- AND HYDROGEN-ISOTOPE RATIOS/

Grown-up trees of C. rosea (girths larger than 7 cm, heights taller th an 2 m) in the Virgin Islands have a strong component of nocturnal CAM -type CO2 fixation as indicated by their deltaC-13 values of almost-eq ual-to - 18 parts per thousand reaching up to the low end of the range typical for CAM (-9 to -18 parts per thousand). Seedlings (girths up to 3.5 cm and heights up to 1.2 m) have a smaller but still notable CO 2-dark fixation as suggested by deltaC-13 values of almost-equal-to - 21 to almost-equal-to -26 parts per thousand, and only very small seed lings appear to be exclusively C3 (deltaC-13 = - 29 parts per thousand ). The larger variation of deltaC-13-values among seedlings suggests t hat seedlings make more flexible use of the options of CO2 dark- and l ight-fixation than adult trees, while the larger variation of deltaD-v alues among trees supports the conclusion, that overall the trees are more flexible in their use of water in transpiration. More negative va lues of deltaC-13 and deltaD in terrestrial plants as compared to thei r epiphytic sympatriotes suggest that the ratio of dark fixation to li ght fixation Of CO2 is smaller in terrestrial plants and that epiphyti c plants transpire more of the water available to them. Leaf-N levels support the assumption of a better supply of the terrestrial plants. T he analyses of stable isotopes and leaf-N levels, which are very suita ble for screening in the field, corroborate the high ecophysiological flexibility of C. rosea as shown by more elaborate experimental approa ches in the laboratory and in the field.