Consistent patterns in leaf lamina and leaf vein carbon isotope composition across ten herbs and tree species.

Wide-spread post-photosynthetic fractionation processes deplete metabolites and plant compartments in (13)C relative to assimilates to varying degrees. Fragmentation fractionation and exchange of metabolites with distinct isotopic signatures across organ boundaries further modify the patterns of plant isotopic composition. Heterotrophic organs tend to become isotopically heavier than the putative source material as a result of respiratory metabolism.