Variability of C-13-labeling in plant leaves

RATIONALE: Plant tissues artificially labeled with C-13 are increasingly used in environmental studies to unravel biogeochemical and ecophysiological processes. However, the variability of C-13-content in labeled tissues has never been carefully investigated. Hence, this study aimed at documenting the variability of C-13-content in artificially labeled leaves. METHODS: European beech and Italian ryegrass were subjected to long-term C-13-labeling in a controlled-environment growth chamber. The C-13-content of the leaves obtained after several months labeling was determined by isotope ratio mass spectrometry. RESULTS: The C-13-content of the labeled leaves exhibited inter- and intra-leaf variability much higher than those naturally occurring in unlabeled plants, which do not exceed a few per mil. This variability was correlated with labeling intensity: the isotope composition of leaves varied in ranges of ca 60 parts per thousand and 90 parts per thousand for experiments that led to average leaf C-13-content of ca +15 parts per thousand and +450 parts per thousand, respectively. CONCLUSIONS: The reported variability of isotope composition in C-13-enriched leaves is critical, and should be taken into account in subsequent experimental investigations of environmental processes using C-13-labeled plant tissues. Copyright (c) 2013 John Wiley & Sons, Ltd.