Response of tree growth and wood structure of Larix kaempferi, Kalopanax septemlobus and Betula platyphylla saplings to elevated CO2 concentration for 5 years exposure in a FACE system

Elevated CO (2) concentration affected biomass partitioning in above-ground biomass, but size and number of water-conducting cells were unchanged in Larix kaempferi, Kalopanax septemlobus and Betula platyphylla. Using a Free-Air CO2 Enrichment (FACE) system, we studied the effect of elevated CO2 on the growth, leaf gas exchange and xylem anatomy of a conifer, Larix kaempferi, and two angiospermous tree species, Kalopanax septemlobus and Betula platyphylla. Two-year-old seedlings were grown at control sites (ambient; 370 ppm) and FACE sites (elevated; 500 ppm) for 5 years. We measured the lumen area and number of water-conducting cells, as well as biomass and leaf gas exchange, and visualized the functional region of water transport using a dye injection experiment. Elevated CO2 did not induce any significant changes in growth or in leaf gas exchange or lumen area of earlywood tracheids in L. kaempferi relative to ambient CO2. In two other tree species, elevated CO2 was found to enhance tree height and total leaf area (LA), with no change in stomatal conductance. In K. septemlobus, there were no changes in lumen area or number of earlywood vessels, or in the functional region of water transport. B. platyphylla also underwent no changes in lumen area or number of vessels, although there was a yearly variation in the size of the vessels. Our results show that 5 years of CO2 exposure did not notably affect the anatomical features of water-conducting cells. This finding suggests that, under elevated CO2, trees respond to changes in water balance due to changes in LA by extending the hydraulically active area of xylem