Physiological controls of the carbon balance of boreal forest ecosystems

Mature boreal forest ecosystems in interior Alaska are large annual carbon sinks. Annual tree production is the largest carbon flux. A model that combined energy, heat, and moisture exchange, tree photosynthesis and respiration, decomposition, and nitrogen mineralization was used to examine the physiological controls of the carbon balance of boreal forests. Simulated annual tree production, forest floor decomposition, nitrogen mineralization, and soil respiration were not significantly different from observed data for nine black spruce Picea mariana, five white spruce Picea glauca, two quaking aspen Populus tremuloides, two paper birch Betula papyrifera and three balsam popular Populus balsamifera forests near Fairbanks, Alaska. The model also reproducted features of observed fertilizaton, soil warming, and litter transplant experiments. Net carbon uptake during tree growth was the largest simulated carbon flux. Differences in the C balance of these forests can be explained, in part, through key physiological parameters that link photosynthesis C allocation, N requirements, litter quality, and foliage longevity. The greatest source of variation in these parameters occurs between coniferous and deciduous life-forms not among species. -from Author