What was done
Five-month-old seedlings of western hemlock were grown in root boxes and subjected to various root-space CO2 concentrations ranging from approximately 90 to 7000 ppm for several hours to determine the effect of soil CO2 concentration on growth, maintenance, and total root respiration.

What was learned
Although elevated CO2 significantly impacted maintenance and total respiration rates, it had no apparent affect on growth respiration.  At a soil CO2 concentration of 1585 ppm, for example, total and maintenance respiration rates were 55 and 60% lower, respectively, than they were at 395 ppm.  In fact, the impact of elevated CO2 was so strong on maintenance respiration, it exhibited an exponential decline of about 37% for every doubling of soil CO2 concentration.  The implications of this observation are important, as maintenance respiration comprised 85% of total respiration in this study.

What it means
This study indicates that as the CO2 content of the air increases, maintenance respiration rates will decline, while growth respiration rates will remain unaffected in western hemlock roots.  Thus, in a future world with greater atmospheric CO2 concentrations, it is likely that western hemlock roots will exhibit reduced respiration rates, which consequently increases carbon sequestration and gross photosynthetic efficiency.