Photosynthetic traits of Siebold's beech seedlings in changing light conditions by removal of shading trees under elevated CO₂.

Abstract

The purpose of this study was to obtain basic information on acclimation capacity of photosynthesis in Siebold's beech seedlings to increasing light intensity under future elevated CO2 conditions. We monitored leaf photosynthetic traits of these seedlings in changing light conditions (before removal of shade trees, the year after removal of shade trees and after acclimation to open conditions) in a 10-year free air CO2 enrichment experiment in northern Japan. Elevated CO2 did not affect photosynthetic traits such as leaf mass per area, nitrogen content and biochemical photosynthetic capacity of chloroplasts (i.e. maximum rate of carboxylation and maximum rate of electron transport) before removal of the shade trees and after acclimation to open conditions; in fact, a higher net photosynthetic rate was maintained under elevated CO2 . However, in the year after removal of the shade trees, there was no increase in photosynthesis rate under elevated CO2 conditions. This was not due to photoinhibition. In ambient CO2 conditions, leaf mass per area and nitrogen content were higher in the year after removal of shade trees than before, whereas there was no increase under elevated CO2 conditions. These results indicate that elevated CO2 delays the acclimation of photosynthetic traits of Siebold's beech seedlings to increasing light intensity.