Keywords: soil respiration, CO2 evolution measurements, online conductivity measurement, soil studies, carbon dioxide, soil pollution, soil contamination, microbial respiration rate
Laboratory test system to measure microbial respiration rate
This study reports a sensible, accurate and economic method for continuous measuring microbial respiration. The measuring principle is an open system, with a continuous air-flow through. Evolved CO2 is absorbed and precipitated as carbonate by a Ba(OH)2 solution, causing a stoichiometrical decrease in ionic strength of the solution and in electrical conductivity. Conductivity and Ba(OH)2 concentration correlate over a range of more than three orders of magnitude with a determination coefficient of r2 = 0.999. Between 20°C and 50°C and Ba(OH)2 concentrations of up to 0.099M, an automated temperature correction was developed. The system detects evolved CO2 quantitatively up to a maximum of 0.22 mmol O2 min-1 (825 mbar, 20°C) before limiting microbial respiration. A maximum CO2 flow of 1.06 mmol min-1 is quantitatively absorbed under these conditions. The method was applied to characterise soil respiration of a soil sample from an agricultural experimental site in Tabasco, Mexico.