Figure 3.

Schematic of progressive ¹⁸O enrichment of leaf water as expected in grass leaves. As source water (solid arrowed lines) exits a vein and moves toward a stoma, it becomes evaporatively enriched in ¹⁸O. This enrichment process creates a concentration gradient of enriched water at the stoma relative to water in the vein, which results in a back diffusion of enriched water (dashed arrowed lines). The mixing of the isotopically distinct water pools results in a slight enrichment of vein water, which then influences ¹⁸O enrichment of leaf water in the next leaf segment, where the process occurs again further enriching vein water.