PARENT SESSION
Oral Session #15: Ecosystem Ecology. Presiding: J. Jenkins.
Monday, August 6, 2001. 1:00 PM to 4:45 PM. Hall of Ideas F.

The radiocarbon signature of soil respiration following fire in Alaskan boreal forest: does disturbance release old soil carbon to the atmosphere?

SCHUUR, EDWARD¹, TRUMBORE, SUSAN¹, ¹

ABSTRACT- Fire in the boreal forest releases carbon stored in vegetation and soil to the atmosphere. Following fire, microbial decomposition is stimulated by inputs of plant detritus and changes in soil microclimate, which results in large losses of carbon. Furthermore, warmer summer soil temperatures and deeper thaw depths in burned ecosystems may make carbon that was previously climatically protected by low soil temperatures susceptible to decomposition. We used radiocarbon measurements to estimate the age of carbon released by soil respiration following fire in two black spruce (Picea mariana) forests in interior Alaska that burned during the summer of 1999. To isolate soil respiration, we established manipulated plots where vegetation was prevented from recolonizing, and paired control plots in nearby unburned forest. Soil respiration radiocarbon signatures in the burned manipulation ranged from +112 to +192‰ and differed significantly from the unburned controls that ranged from +100 to +130‰. Burned plots appear to respire older carbon than unburned forest, which could either be due to the stimulation of decomposition of intermediate age soil organic matter pools, to the lack of plant respiration that reflects the current atmospheric radiocarbon signature of +92‰, or both. At least during the initial phase following fire, these data suggest that carbon flux from soil is dominated by soil organic matter pools with decadal scale turnover times.

KEY WORDS: carbon, soil respiration, radiocarbon, fire