Effects of elevated CO2 concentration on root and needle anatomy and physiological functions in Pinus koraiensis seedlings

AimsThe impacts of CO₂ concentration on the anatomy and physiology of plant roots have rarely been studied. Here we studied the effects of elevated CO₂ on anatomical and physiological traits of needles and root tips in Pinus koraiensis seedlings. Our objectives were: 1) to examine how the anatomy of needles and root tips change under doubled CO₂ concentration treatment; and 2) to explore physiological responses of needles and root tips to the rising CO₂ concentration; and 3) to reveal potential relationships of physiological trait changes between needles and root tips.MethodsThree-year-old seedlings of P. koraiensis were grown in CO₂ chambers under doubled and ambient CO₂ concentrations (350 and 700 µmol·mol^-1). Physiological traits of needles were measured by the LI-6400 portable photosynthesis system during the experiment. After 5 months, needles and root tips were sampled to determine their anatomical characteristics. Theoretical hydraulic conductivity of needles and root tips were calculated based on the Hagen-Poiseuille’s Law.Important findings Elevated CO₂ concentration had a significant influence on the anatomical characteristics of needles and root tips in P. koraiensis seedlings. Under doubled CO₂ concentration, needles had a lower stomatal desnity, greater areas of leaf mesophyll, phloem and xylem. In comparision, root tips under doubled CO₂ concentration had a larger diameter, a greater cortical thickness and a larger number of cortical cell layer. Physiological traits of needles and root tips also changed substantially under the elevated CO₂ concentration, such as increases in needle photosynthetic rate and water use efficiency, xylem cavitation resistance of roots, as well as decreases in stomatal conductance, transpiration rate and root hydraulic conductivity. These results suggest that the anatomical structure and physiological function of leaf and root respond simultaneously to elevated CO₂ concentration. Future studies should not only focus on the impact of global climate change on aboveground organs and fuctions, but also to the belowground counterparts.