Differential 18 O enrichment of leaf cellulose in C 3 versus C 4 grasses

We show that differences in the oxygen isotope ratio of leaf water between C3 and C4 grasses (five species of each photosynthetic type) become less distinct as relative humidity increases, and that 18O leaf water differences translate directly to the oxygen isotope ratio of leaf cellulose. A conceptual model is presented that is based on grass blade growth characteristics and observed patterns of progressive enrichment in grasses. The Barbour and Farquhar (2000) model was capable of explaining the oxygen isotope ratio of bulk leaf cellulose of C3 and C4 grasses grown under a variety of growth conditions.