Establishing a grassland signature in veins: O-18 in the leaf water of C-3and C-4 grasses

We show that O-18 evaporative enrichment of bulk leaf water in grass specie s can be significantly more enriched than predicted by the Craig-Cordon mod el, with C-4 grasses considerably more enriched than Cs grasses. Our result s suggest that the unanticipated O-18 leaf water enrichment of grasses is a ttributable to the progressive evaporative enrichment along parallel veins (a function of both leaf length and interveinal distance), a pattern that d oes not occur in Dicotyledonous species. We propose that the differential O -18 enrichment of grasses will result in distinct (COO)-O-18-O-16 biospheri c signals from grassland and forest ecosystems, allowing for further partit ioning of terrestrial carbon fluxes.