Variations in δ13C of different plant organs: implications for post-photosynthetic fractionation

Abstract

Compared to photosynthetic fractionation, the mechanism of post-photosynthetic carbon isotope fractionation is not well understood. The aim of this study was to investigate post-photosynthetic fractionation in both above and below ground tissues and to evaluate potential hypotheses explaining differences in carbon isotope composition ({delta}13C) among different plant organs, which can provide valuable insights into plant physiology. The results revealed that there is no significant day-night difference in{delta} 13C of twig phloem water soluble organic materials (WSOM), which could be explained by the unrestricted exchange of triose-phosphates between the chloroplast and cytoplasm and a time lag for carbohydrate exportation. Further, we found that{delta} 13C of twig phloem WSOM is more sensitive to plant water status than leaf WSOM. Analysis of{delta} 13C in different plant organs showed that the greatest 13C enrichment was recorded in stem phloem. Divergences in{delta} 13C of phloem WSOM among different plant organs were not likely to be explained by respiratory fractionation or time lag and were ascribed to transport of carbohydrates across organ boundaries and metabolic processes. Our study demonstrated that post-photosynthesis fractionation could not be ascribed to a single, unifying hypotheses; instead, it is the result of multiple processes.\n\nHighlight{delta}13C of twig phloem water soluble organic materials varied no clear diel pattern. In the leaf-twig-stem-root sequence, the greatest 13C enrichment was recorded in stem phloem.