Figure 2.

The δ¹⁸O of chloroplast CO₂ plotted against the δ¹⁸O of water at evaporative sites in R. communis leaves during dark respiration. In this experiment, air entering the leaf chamber had an average CO₂ partial pressure of 314 μbar, and air exiting the chamber had an average CO₂ partial pressure of 347 μbar. The broken line on the graph represents the relationship expected if chloroplast CO₂ were in full oxygen isotope equilibrium with water at the evaporative sites. The δ¹⁸O values are presented relative to VSMOW. The δ¹⁸O of irrigation water fed to the plants was −7.2‰.