A reexamination of cellulose carbon-bound hydrogen δD measurements and some factors affecting plant-water D/H relationships

The method of Epstein et al. (1976) for analysis of D/H ratios of cellulose carbon-bound hydrogen has been modified. This modified “renitration” method yields δD values which are in agreement with those obtained by the sodium chlorite delignification method. Comparison of results obtained by the renitration method with the published results of Epstein et al. (1976) indicate some differences in the δD values of individual samples. However, the overall plant-water δD relationship determined by Epstein et al., is not greatly changed upon redetermination by the renitration method. Additional data from a variety of plants representing a wide geographical range reveal that relative humidity is an important variable in determining the δD value of cellulose C-H hydrogen on this inter-regional scale. The role of relative humidity can be reasonably explained by a leaf water model that assumes an isotopic steady-state during transpiration. These results reaffirm the conclusion of Epstein et al., that the δD variations of the source water are the dominant control of the δD variations of cellulose C-H hydrogen from naturally grown plants. Thus, there is an expectation that these cellulose δD variations can have climate significance