Factors influencing the stability of labelled microbial materials in soils

Abstract

The effect of freshly added substrate on carbon turnover of a microbial population and the priming action on stabilized soil organic constituents were investigated in the laboratory. 13C-labelled glucose. NH 4NO 3, or both were added to samples of a Brown Chernozemic soil which had been initially amended with 14C-glucose and incubated 2 months under field conditions. At the end of 14 days laboratory incubation. 39 per cent and 33 per cent of the 13C had been respired as CO 2 from the glucose and glucose plus NH 4NO 3 treatments, respectively. These two treatments resulted in a marked priming of native 12C during the second and third days of incubation and a second priming peak during the fifth day. In contrast, there was only a small priming action of the 14C-labelled materials. Addition of NH 4NO 3 by itself had no effect on the amount of 12C or 12C respired. Appreciable amounts of 14C were mineralized following treatments known to partially sterilize soil. Freezing and thawing was more effective than wetting and drying, but less effective than CHCl 3 vapour in releasing stabilized 14C materials. The amount of labelled- 14C mineralized during incubation after treatment with chloroform vapour was greater than could he accounted for by the decrease in soil biomass.