Effects of Elevated Atmospheric Carbon Dioxide and Temperature on Soil Respiration in a Boreal Forest Using gamma~13C as a Labeling Tool

摘要

This study examines the effect of elevated atmospheric carbon dioxide [CO_2] (+340 ppm, 13~C-de-pleted) and/or elevated air temperature (2.8-3.5 deg C) on the rate and 813C of soil respiration. The study was conducted in a boreal Norway spruce forestusing temperature-controlled whole-tree chambers and 13~C as a marker for root respiration. The 513~C of needle carbohydrates was followed after the onset of the CO_2 treatment in August 2001 and during a 2.5-week period in the summer of 2002. Averaged over the growing seasons of 2002 and 2003, we observed a 48% and 62% increase, respectively, in soil respiration in response to elevated [CO_2], but no response to elevated air temperature. The percentage increase in response to elevated [CO_2] varied seasonally (between 10% and 190% relative to the control), but the absolute increase varied less (39 +- 11 mg C m~(-2) h~(-1); mean +- SD). Data onC of soil respiration indicate that this increase in soil respiration rate resulted from increased root/rhi-zosphere respiration of recently fixed carbon. Our results support the hypothesis that root/rhizo-sphere respiration is sensitive to variation in substrate availability.