Establishing a grassland signature in veins:: 18O in the leaf water of C3 and C4 grasses

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