Water stress and CO2concentration interactions affect carbon isotope signatures of leaf and phloem organic matter

Investigation of δ 13 C 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 CO 2 concentrations (C a ) × five soil water contents (SWC) were conducted using Platycladus orientalis saplings to investigate the interaction of water stress and CO 2 concentration on δ 13 C of leaf and twig phloem WSOM. Under the lowest SWC, the δ 13 C of leaf and twig phloem WSOM had the most positive values at any C a and their values decreased as C a increased. However, at improved soil water conditions, the greatest values of δ 13 C of leaf and twig phloem WSOM were mostly observed at C 600 . In addition, a more significant relationship between SWC and δ 13 C of twig phloem WSOM than that between SWC and δ 13 C of leaf WSOM demonstrated that δ 13 C of twig phloem WSOM is a more sensitive indicator of SWC. Twig phloem WSOM was generally 13 C-depleted compared with leaf WSOM for potential post-photosynthetic fractionation, and the 13 C discrimination from leaves to twig phloem was insensitive to the interaction between SWC and C a . Clearly, interacting effects play a more important role in photosynthetic fractionation than in post-photosynthetic fractionation. Highlight The δ 13 C of leaf and twig phloem WSOM exhibited the most positive values at C 400 ×35%–45% FC. Post-photosynthetic fractionation from leaf to twig was not be impacted by the interacting effects.