CHANGES IN C-STORAGE BY TERRESTRIAL ECOSYSTEMS - HOW C-N INTERACTIONS RESTRICT RESPONSES TO CO2 AND TEMPERATURE

A general model of ecosystem biogeochemistry was used to examine the responses of arctic tundra and temperate hardwood forests to a doubling of CO2 concentration and to a 5-degrees-C increase in average growing season temperature. The amount of C stored in both ecosystems increased with both increased CO2 and temperature. Under increased CO2, the increase in C storage was due to increases in the C:N ratio of both vegetation and soils. Under increased temperature, the increased C storage in the forest was due to a shift in N from soils (with low C:N ratios) to vegetation (with high C:N ratios). In the tundra, both a shift in N from soils to vegetation and an increase in C:N ratios contributed to increased C storage under higher temperatures. Neither ecosystem sequestered N from external sources because the supply rate was low.