Carbon turnover in a range of allophanic soils amended with 14C-labelled glucose
1994
Saggar, S. | Tate, K.R. | Feltham, C.W. | Childs, C.W. | Parshotam, A.
The influence of soil allophane (a short-range-order mineral) content on organic-C turnover was determined with 14C-labelled glucose. Samples from four soils, providing a range of allophane, organic C, clay contents, and some other characteristics, were incubated with 14C-labelled glucose for 28 days. During incubation, microbial biomass 12C and 14C were determined using the fumigation-extraction technique. The amounts of 12CO2 and 14CO2 evolved during incubation were also monitored, and residual 14C concentrations determined. Biomass 14C Was highest in the soil with the highest allophane content (13%) and least in the soil with least allophane content (<2%). In contrast, 14CO2 production from the [14C]glucose was highest (63%) in the soil with least allophane content and lowest (54%) in the soil with the most allophane. It was concluded, from first-order decay rate constants for residual 14C and exponential decay rate constants for biomass 14C, that allophane retards the turnover rates of 14C derived from added glucose by stabilization of microbial biomass, and also by protection of microbial products. During a 28 day incubation, ca 0.8% more C was diverted from respired CO2 to new biomass with each 1% increase in allophane content. For allophanic soils, inclusion of mineral surface area rather than clay content should provide a better quantification of the organic matter turnover rate.
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