A modelling study of the effects of changes in atmospheric CO2 concentration, temperature and atmospheric nitrogen input on soil organic carbon storage

Abstract

There has been recent debate as to whether the world's soils are currently a net source or sink for carbon. This question was investigated with a model of soil organic matter coupled to a simple biochemically-based productivity model. In line with our plant physiological understanding, plant productivity was predicted to increase strongly with atmospheric CO₂ concentration at higher temperatures, but to respond less to CO₂ concentration at lower temperatures. The model showed equilibrium soil organic carbon contents to increase with increasing atmospheric CO₂concentration, but to decrease with increasing temperature. Equilibrium soil organic carbon contents also increased with increasing rates of nitrogen input from atmospheric deposition or biological fixation. Time course analyses of changes in stored organic carbon suggest that approaches to new equilibria take many centuries, especially at lower temperatures. As a consequence, in response to a step increase in atmospheric CO₂ concentration, carbon storage in warm soils would continue to increase for more than 500 years, and the change would be even slower in cooler soils. The model was then used to estimate changes in soil organic carbon storage over the past 130 years in response to recorded changes in CO₂ concentration and temperature. The model suggests that there may have been an increase in soil organic carbon storage in warmer regions, whereas in cooler regions, soil organic carbon contents are likely to have decreased. Nitrogen deposition rates, which have increased due to atmospheric pollution, are likely to have caused increased soil carbon storage in heavily polluted areas but this is not likely to have had more than a small impact in a global context. DOI: 10.1034/j.1600-0889.1993.t01-3-00002.x