I would suggest that there should be subcategories for "Carbon Isotope Discrimination", as what is mainly measured is "Carbon Isotope Composition" on a specific material, mainly either bulk leaves, leaf sugars, bulk wood or wood extracted cellulose; also most of the time carbon isotope composition of atmospheric CO2 is not estimated but taken from the literature, which can bias the calculation of Carbon Isotope Discrimination; therefore it seems necessary to me to be able to precise in the ontology if actually composition or discrimination has been measured.