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

We show that (18)O evaporative enrichment of bulk leaf water in grass species can be significantly more enriched than predicted by the Craig–Gordon model, with C(4) grasses considerably more enriched than C(3) grasses. Our results suggest that the unanticipated (18)O 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 (18)O enrichment of grasses will result in distinct C(18)O(16)O biospheric signals from grassland and forest ecosystems, allowing for further partitioning of terrestrial carbon fluxes.