The relationship of 15N excess with 13C excess in intact roots of mature trees of messmate (E. obliqua), candlebark (E. rubida) and narrow-leaf peppermint (E. radiata) that had been incubated in 2-13C2 15N-glycine. Glycine uptake by the three species was measured at three sites on each of four occasions. A total of 108 measurements are shown (3 species × 3 sites × 4 dates × 3 replicate trees). Relationships did not differ among dates, sites or species (ANCOVA) and thus a common relationship was fitted. Also shown is the expected 2:1 relationship if all glycine were taken up intact.