Relationships between growth and carbon Isotope Discrimination for some Pasture Species

Carbon isotope discrimination (A) by plants can be directly related to plant water-use efficiency (W, total plant dry matter, OM, per water transpired) and used in selection to achieve greater W. As \V (and A) is a complex characteristic, there maybe inherent relationships between it and plant productivity. A range of pasture cultivars (of temperate grasses and legumes) were grown in pots (lo c. 50 days) and \V, A and total dry mailer measured. Among cultivars the relationship between W and A was negative and significant as was the relationship between A and total OM accumulation. A further experiment showed that at an earlier stage (c. 25 days) the relationship between total dry matter and A was positive for grass cultivars and negative for legume cultivars. These results arc discussed with respect to the usefulness of W as a physiological trait and the interpretation of apparent relationships between dry matter accumulation and A.