Abstract
Soil surface carbon dioxide (CO 2 ) flux ( R S ) was measured for 2 years at the Boreal Soil and Air Warming Experiment site near Thompson, MB, Canada. The experimental design was a complete random block design that consisted of four replicate blocks, with each block containing a 15 m × 15 m control and heated plot. Black spruce [ Picea mariana (Mill.) BSP] was the overstory species and Epilobium angustifolium was the dominant understory. Soil temperature was maintained (∼5 °C) above the control soil temperature using electric cables inside water filled polyethylene tubing for each heated plot. Air inside a 7.3‐m‐diameter chamber, centered in the soil warming plot, contained approximately nine black spruce trees was heated ∼5 °C above control ambient air temperature allowing for the testing of soil‐only warming and soil+air warming. Soil surface CO 2 flux ( R S ) was positively correlated ( P 2 flux ( R S ) was 24% greater in the soil‐only warming than the control in 2004, but was only 11% greater in 2005, while R S in the soil+air warming treatments was 31% less than the control in 2004 and 23% less in 2005. Live fine root mass ( P