Bioavailable organic carbon in wetland soils across a broad climogeographic area

Abstract

Soils from a broad climogeographic region of the U.S., ranging from Alaska to Louisiana and Texas, were obtained from the NRCS National Soils Laboratory in Lincoln, Nebraska. Soils were also collected in the summer of 1996 from upland and poorly drained areas in northern Alaska for comparison of biological properties and to determine the effects of drying on estimation of microbial biomass and activity. Air-dried soils were moistened and incubated 48 h, during which time CO₂ evolution was measured. Following the preincubation, microbial biomass was determined using a modification of the chloroform-fumigation-incubation method to accommodate limited sample quantity. Carbohydrates were determined using bicinchoninic acid reagent and total extractable carbon was determined by analysis of 0.5-M K₂SO₄ extracts with a total carbon analyzer. The objectives of this study were to elucidate geographical trends and meaningful relationships between the bioavailable C parameters. Soil microbial biomass, determined by chloroform fumigation incubation, correlated best with organic C and basal respiration with subtraction of unfumigated controls. Extraction of C with hot water was a rapid, simple procedure that provided the best predictor of soil respiration. Potassium sulfate-extractable carbon was consistently lower than hot water extractable C. Soils from northern states tended to contain more organic carbon than soils in southern states, however, not necessarily more bioavailable C. Detecting geographical trends for bioavailable C proved more difficult due to numerous factors such as topographic position, surface vegetation, climate, and land use.