Compensation Point and Isotopic Characteristics of C 3 /C 4 Intermediates and Hybrids in Panicum

Abstract

Leaf CO(2) compensation points and stable hydrogen, oxygen and carbon isotope ratios were determined for Panicum species including C(3)/C(4) intermediate photosynthesis plants, hybrids between C(3)/C(4) intermediates and C(3) plants, C(3) and C(4) plants in the Panicum genus as well as several other C(3) and C(4) plants. C(3) plants had the highest compensation points, followed by hybrids, C(3)/C(4) intermediates, and C(4) plants. delta(13)C values of cellulose nitrate and saponifiable lipids from C(4) plants were about 10 per thousand higher than those observed for cellulose nitrate and saponifiable lipids of C(3)/C(4) intermediates, hybrids, and C(3) plants. Oxygen isotope ratios of cellulose as well as those of leaf water were similar for all plants. There was substantial variability in the deltaD values of cellulose nitrate among the plants studied. In contrast, such variability was not observed in deltaD values of water distilled from the leaves, nor in the deltaD values of the saponifiable lipids. Variability in deltaD values of cellulose nitrate from C(3)/C(4) intermediates, hybrids, C(3), and C(4) plants is due to fractionations occurring during biochemical reactions specific to leaf carbohydrate metabolism.