Dimethyl sulphoxide reduction as a sensitive indicator of microbial activity in soil: the relationship with microbial biomass and mineralization of nitrogen and sulphur
1993
Sparling, G.P. | Searle, P.I.
The reduction of dimethyl sulphoxide (DMSO) to dimethyl sulphide (DMS) in soil was measured in a range of 47 New Zealand topsoils and humus samples. The relationships between the rate of DMSO reduction and soil type and land use, organic C and N, the soil microbial C estimated by the substrate-induced-respiration (SIR) method, mineralization of N under anaerobic (waterlogged) incubation and the mineralization of organic S, were investigated. DMSO was reduced rapidly in all soils and rates ranged between 180 and 8124 ng DMS g-1 soil h-1, with the coefficient of variance being typically < 10%. Reduction was significantly correlated with the organic C and N content of the 44 mineral soils (r = 0.61 and 0.62, respectively), anaerobically-mineralized N (r = 0.80). microbial biomass C (r = 0.81), and aerobically mineralized SO4-S (r = 0.60). The rate of DMSO reduction per unit of microbial C was approximately constant over the whole range of soil types and land uses. The reduction of DMSO was shown to be much more sensitive to the presence of Cr(VI) or As(V) than was the SIR response. DMSO reduction by axenic roots was from 6 to 46 microgram DMS g-1 root C h-1, compared to 1177 +/- 420 microgram DMS g-1 microbial C h-1 (mean and SD). The sensitivity and reproducibility of the assay make the technique potentially useful for the study of microbial activity in aggregates, rhizosphere samples and contaminated soils.
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