Soil and Root Respiration Under Elevated CO 2 Concentrations During Seedling Growth of P inus sylvestris var. sylvestriformis

Abstract

The objectives of this study were to investigate the effect of higher CO 2 concentrations (500 and 700 μmol mol −1) in atmosphere on total soil respiration and the contribution of root respiration to total soil respiration during seedling growth of Pinus sylvestris var. sylvestriformis. During the four growing seasons (May-October) from 1999 to 2003, the seedlings were exposed to elevated concentrations of CO 2 in open-top chambers. The total soil respiration and contribution of root respiration were measured using an LI-6400-09 soil CO 2 flux chamber on June 15 and October 8, 2003. To separate root respiration from total soil respiration, three PVC cylinders were inserted approximately 30 cm deep into the soil in each chamber. There were marked diurnal changes in air and soil temperatures on June 15. Both the total soil respiration and the soil respiration without roots showed a strong diurnal pattern, increasing from before sunrise to about 14:00 in the afternoon and then decreasing before the next sunrise. No increase in the mean total soil respiration and mean soil respiration with roots severed was observed under the elevated CO 2 treatments on June 15, 2003, as compared to the open field and control chamber with ambient CO 2. However, on October 8, 2003, the total soil respiration and soil respiration with roots severed in the open field were lower than those in the control and elevated CO 2 chambers. The mean contribution of root respiration measured on June 15, 2003, ranged from 8.3% to 30.5% and on October 8, 2003, from 20.6% to 48.6%.