Articles | Volume 12, issue 6
Research article
20 Mar 2015
Research article |  | 20 Mar 2015

Multi-isotope labelling of organic matter by diffusion of 2H/18O-H2O vapour and 13C-CO2 into the leaves and its distribution within the plant

M. S. Studer, R. T. W. Siegwolf, M. Leuenberger, and S. Abiven

Abstract. Isotope labelling is a powerful tool to study elemental cycling within terrestrial ecosystems. Here we describe a new multi-isotope technique to label organic matter (OM).

We exposed poplars (Populus deltoides × nigra) for 14 days to an atmosphere enriched in 13CO2 and depleted in 2H218O. After 1 week, the water-soluble leaf OM (δ13C = 1346 ± 162‰) and the leaf water were strongly labelled (δ18O = −63 ± 8, δ2H = −156 ± 15‰). The leaf water isotopic composition was between the atmospheric and stem water, indicating a considerable back-diffusion of vapour into the leaves (58–69%) in the opposite direction to the net transpiration flow. The atomic ratios of the labels recovered (18O/13C, 2H/13C) were 2–4 times higher in leaves than in the stems and roots. This could be an indication of the synthesis of more condensed compounds in roots and stems (e.g. lignin vs. cellulose) or might be the result of O and H exchange and fractionation processes during phloem transport and biosynthesis.

We demonstrate that the three major OM elements (C, O, H) can be labelled and traced simultaneously within the plant. This approach could be of interdisciplinary interest in the fields of plant physiology, palaeoclimatic reconstruction or soil science.

Short summary
We present a new technique to label organic matter (OM) at its place of formation by the application of 13C, 18O and 2H through the gaseous phase. The label diffused into leaves was incorporated into assimilates and was detected in plant tissues. This technique can be applied in soil sciences, e.g. to trace the decomposition pathways of soil OM inputs, or in plant physiology and palaeoclimatic reconstruction, e.g. to further investigate the origin of the 18O and 2H signal in tree ring cellulose.
Final-revised paper