Interpretation of oxygen isotope composition of leaf material
Graham D. Farquhar, Margaret M. Barbour, Beverley Henry
Abstract
In this chapter, the authors provide theoretical background to, and analytical procedures for, oxygen isotope composition in organic material in order to provide a new tool for the study of plant-environment interactions. Measurements of the oxygen isotope ratio of plant organic matter (typically cellulose in tree rings) assist in reconstruction of palaeoclimatic data. Ignoring for the moment the evaporation from a file of cells and considering only a uniformly evaporating leaf, the authors would expect the isotopic composition of chloroplast water to be close to that of the evaporating cell walls, but somewhat towards that of source water. The quantitative nature of that term ‘somewhat’ is a matter of debate and uncertainty at the present. Many intermediates leading to cellulose synthesis contain carbonyl oxygen, so that the exchange reaction becomes important in determining the isotopic signature of plant organic material.