Citation. Cook, B. D.; Allan, D. L. 1992. Dissolved organic carbon in old field soils: total amounts as a measure of available resources for soil mineralization. Soil Biology and Biochemistry 24:585-594.   [1026  LTER]

Summary. Dissolved organic carbon (DOC) and C and N mineralization were measured during a 210 day regulated in vitro incubation of soils from an old field successional sequence at Cedar Creek Natural History Area. The objective of the study was to evaluate the hypothesis that soil DOC constitutes a readily-available microbial resource, and that DOC concentrations are related to rates of biological decomposition and associated nutrient release from soil organic matter. Soils from five previously cultivated old fields undergoing secondary succession and an oak savanna were selected because they had demonstrated different patterns of C and N cycling. Although amounts of total C differed dramatically (496-1371 micromol g-1), DOC concentrations of all soils at the time of collection were between 0.70 and 1.30 micromol g-1. During the incubation, total and relative DOC concentrations generally remained constant or increased while mineralization rates decreased. When all soils and incubation intervals were considered there was no obvious relationship between DOC and instantaneous rates of mineralization. Asymptotic exponential response curves did describe positive associations between DOC and CO2-C mineralization rates at early incubation times (R2 = 0.98 for 14 and 35 days), but not later. Similar models did not show a strong relationship between DOC and net-N mineralization rates. By the end of the incubation, the DOC pool could potentially supply 1.5-3.4 days of total C mineralization, but the instantaneous C mineralization rate at any given DOC concentration was 3-10 times lower than at 14 days. These results reflect decreased DOC utilization relative to supply, and could be caused by the accumulation of recalcitrant DOC