Relationship of 0.5 m K2SO4 extractable anthrone-reactive carbon to indices of microbial activity in forest soils

The relationship between soluble hexose sugars, measured as 0.5 M K2SO4 extractable anthrone-reactive C (KARC), and indices of microbial activity and short-term C turnover was studied in forest mineral soils of Western Montana. Twelve forest soils were collected and analyzed fresh for KARC, microbial biomass C, 3 d respiration rates, and potentially mineralizable N (PMN). These 12 soils were later exposed to a 10 d moist conditioning incubation at 25°C and then analyzed for KARC, hot-water extractable anthrone-reactive carbon (HARC), and 3 d respiration rates. Regression analysis was used to assess the relationship between both fresh and conditioned KARC and indices of microbial activity. The sensitivity of both KARC and HARC to changes in available C was tested by monitoring changes in these indices following cellulose and plant litter additions to soils and following drying and re-wetting of soils. Conditioning incubation of soils under controlled laboratory conditions prior to extraction with K2SO4 resulted in a strong linear relationship between KARC and short-term respiration rates (R2=0.92) and metabolic quotient (qCO2=respiration rate/microbial biomass C) (R2=0.89); whereas KARC in fresh soils was found to be only weakly correlated (R2=0.28) with 3 d respiration rates and qCO2 (R2=0.47). Hot-water extracted anthrone-reactive carbon (ARC) was not significantly correlated with 3 d respiration rates or qCO2 in conditioned soils, but was strongly correlated with total C (R2=0.81) and PMN (R2=0.76). Drying of soils prior to extraction resulted in a large and inconsistent increase in KARC. This method appears to correlate closely with indices of microbial activity in forest soils as long as soils are conditioned for 10 d prior to extraction.