A NEW APPROACH TO DETERMINE SOIL MICROBIAL BIOMASS BY CALORIMETRY

SESTO CABRAL M. E.;; SIGSTAD E.E.

Lugo, Galicia, España

Conferencia; XVI ISBC (Internacional Society for Biological Calorimetry); 2010

Universidad de Santiago de Compostela

Several methods were developed to determine soil microbial biomass (SMB). The substrate induced respiration (SIR) is based on the activation of the soil microbial community by the addition of glucose and the resulting initial maximal respiration is used to estimate the SMB. As soil respiration could by successfully measured by calorimetry in this work we present a new approach to determine SMB using this technique. Soil samples were collected and stored at 4°C until used. Soil (1g) amended with 2 mg glucose g-1 al 60 % of water holding capacity was placed in the calorimeter al 25°C. Thermal power (P1) was recorded for 2 h. Then, a vial containing a solution of 0,5 N NaOH was introduced and values of Thermal power was recorded again. After 2h, the vial was removed and values of were converted to specific thermal power . The specific rate of CO2 / nmol evolution was calculated by pasting twice in a worksheet of an Origin 6.0 computer program the curve obtained. From one, the p values due to the CO2 evolution were eliminated. Then, this curve was substracted from the original curve and further integrated to obtain q in mJ g-1. This heat value was divided by the heat of neutralization of CO2 with NaOH and by the time of measurement. Values of rCO2 were converted into SMB / g-1 by using the molar volume and a factor of 25,3. Conventional SIR method was also performed. Log values of p were linearly correlated with log values of SMB as previously found. Strinkingly the equation relating both parameters was not significantly different from the previously reported. Calorimetric SMB values were 1.3 times lower than those obtained by SIR.