A simple automated system for measuring soil respiration by gas chromatography

An automated dynamic closed chamber system for CO(2) sampling and analysis was developed for the measurement of soil respiration under laboratory conditions. The system is composed by a gas chromatograph linked to a fully computerised sampling system composed by 16 sample jars and 2 multiposition valves. Besides CO(2), the system can automatically and simultaneously measure CH(4), N(2)O and other gases of environmental interest. The detection limits of the system for CO(2), N(2)O and CH(4) were 2, 1 and 4ppmv, respectively. The accuracy of the system, expressed as percent bias, was -0.88, -0.94 and -3.17% for CO(2), N(2)O and CH(4), respectively, with relative standard deviation of 0.42, 0.68 and 0.61%. Measurement of CO(2) evolved following acidification of a known amount of reagent grade CaCO(3) showed a standard recovery of 96.8+/-2.5% reached within 30s after acidification. A linear response of CO(2) respiration was obtained for a wide range of operative conditions (5-60min accumulation time, 10-80g soil sample size, 10-60mLmin(-1) air flow rate, 15-25 degrees C temperature of incubation) demonstrating the flexibility of the system, which allows for the measurement of soil samples characterised by different rates of gas evolution. Moreover, the results obtained with soil samples showed that within the above conditions the proposed system is not affected by potential limitations of static closed chamber systems such as CO(2) dissolution in the soil solution, reduced rate of CO(2) diffusion from soil to headspace and CO(2) inhibition of microbial activity. The system was also capable to detect significant changes in N(2)O emissions from soil amended with different amounts of glutamic acid. The automatic and frequent measurements provided by the system make possible an accurate description of the dynamics of gas evolution from soil samples under laboratory conditions.