Soil temperature, nitrogen mineralization, and carbon source-sink relationships in boreal forests

Boreal forests contain large quantities of soil carbon, prompting concern that climatic warming may stimulate decomposition and accentuate increasing atmospheric CO₂ concentrations. While soil warming increases decomposition rates, the accompanying increase in nutrient mineralization may promote tree growth in these nutrient-poor soils and thereby compensate for the increased carbon loss during decomposition. In modelled black spruce Picea mariana, white spruce Picea glauca and paper birch Betula papyrifera forests, decomposition increased with the soil warming caused by a 5°C increase in air temperature, but increased nitrogen mineralization promoted tree growth, offsetting the increased carbon loss during decomposition. In the black spruce forest, increased tree production was maintained for the 25 yr of simulation. Whether this can be maintained indefinitely is unknown. In the birch forest, tree production increased to prewarming levels after c10 yr. Analyses examined only the consequences of belowground feedbacks that affect ecosystem carbon uptake with climatic warming. -from Authors