Water stress and CO2 concentration interactions affect carbon isotope signatures of leaf and phloem organic matter

Abstract

Investigation of {delta}13C of leaf and twig phloem water-soluble organic material (WSOM) is a promising approach for analysis of the effects of environmental factors on plant performance. In this study, orthogonal treatments of three CO2 concentrations (Ca) x five soil water contents (SWC) were conducted using Platycladus orientalis saplings to investigate the interaction of water stress and CO2 concentration on {delta}13C of leaf and twig phloem WSOM. Under the lowest SWC, the {delta}13C of leaf and twig phloem WSOM had the most positive values at any Ca and their values decreased as Ca increased. However, at improved soil water conditions, the greatest values of {delta}13C of leaf and twig phloem WSOM were mostly observed at C600. In addition, a more significant relationship between SWC and {delta}13C of twig phloem WSOM than that between SWC and {delta}13C of leaf WSOM demonstrated that {delta}13C of twig phloem WSOM is a more sensitive indicator of SWC. Twig phloem WSOM was generally 13C-depleted compared with leaf WSOM for potential post-photosynthetic fractionation, and the 13C discrimination from leaves to twig phloem was insensitive to the interaction between SWC and Ca. Clearly, interacting effects play a more important role in photosynthetic fractionation than in post-photosynthetic fractionation.\n\nHighlightThe {delta}13C of leaf and twig phloem WSOM exhibited the most positive values at C400x35%-45% FC.\n\nPost-photosynthetic fractionation from leaf to twig was not be impacted by the interacting effects.