Oxygen and Hydrogen Isotopic Ratios in Plant Cellulose

The variations of the D/H and ^(18)O/^(16)O ratios of nonexchangeable hydrogen and oxygen in plant cellulose reveal systematic differences between terrestrial plant groups. The slope of δD versus δ^(18)O of cellulose from a variety of aquatic plants is close to 8 (the meteoric water value), while the slope for a number of terrestrial species is greater than or equal to about 24. Two models involving incorporation of CO_2 and H_2O into cellulose precursors are proposed to account for these differences. Effects of evaporative transpiration on the isotopic composition of water in leaves are measured and discussed in the context of these models