Theoretical Analysis of the Long‐Term Dynamics of Carbon and Nitrogen in Soils

Carbon and nitrogen turnover in soils having continuous inputs of litter is described using theory developed for single cohorts of litter. Fresh litter is characterized by its quality (how easily it is decomposed by microbes) and its N:C ratio. The decomposition process is described as a continuum and no transition between litter and humus is recognized. Equations are derived for the amounts of carbon and nitrogen in the soil at steady state. Depending upon the microbial production—to—assimilation ratio when substrate of the lowest quality (most—degraded litter) is decomposed, steady state implies either constant or linearly increasing amounts of soil carbon and nitrogen. Comparisons are made between theoretically estimated and observed relations between soil carbon and nitrogen turnover rates for a large range of terrestrial ecosystems, as well as carbon and nitrogen stocks in a Scots pine forest soil.