Effects of elevated CO<inf>2</inf> concentration on root and needle anatomy and physiological functions in Pinus koraiensis seedlings

Abstract

Aims The 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 nee- dles and root tips. Methods Three-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 de- termine their anatomical characteristics. Theoretical hydraulic conductivity of needles and root tips were calcu- lated 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. Physio- logical 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