[Effects of soil water stress and atmospheric CO concentration on photosynthetic and post-photosynthetic fractionation].

Analysis of plant photosynthesis and post-photosynthetic fractionation can improve our understanding of plant physiology and water management. By measuring δC in the atmosphere, and δC of soluble compounds in leaves and branch phloem of Platycladus orientalis, we examined discrimination pattern, including atmosphere-leaf discrimination during photosynthesis (ΔC) and leaf-twig discrimination during post-photosynthesis (ΔC), in response to changes of soil water content (SWC) and atmospheric CO concentration (C). The results showed that ΔC reached a maximum of 13.06‰ at 95%-100% field water-holding capacity (FC) and C 400 μmol·mol, and a minimum of 8.63‰ at 35%-45% FC and C 800 μmol·mol. Both stomatal conductance and mesophyll cell conductance showed a significant linear positive correlation with ΔC, with a correlation coefficient of 0.43 and 0.44, respectively. ΔC was not affected by SWC and C. Our results provide mechanism of carbon isotopes fractionation and a theoretical basis for plant survival strategies in response to future climate change.