Microbial biomass dynamics during the decomposition of glucose and maize in metal-contaminated and non-contaminated soils

Abstract

Metal-contaminated soils (produced by past long-term applications of contaminated sewagesludge) from the Woburn Market Garden Field Experiment were previously shown to contain only about half the amounts of microbial biomass as other soils from the experiment which received farmyard manure during the same period. In some cases, the amounts of biomass in the metal-contaminated soils were even smaller than in other soils from the experiment which received inorganic fertilizer throughout. It is possible that the metals were causing decreased efficiency of substrate utilization by the microbial biomass, leading, in turn, to a smaller microbial population. This was investigated in a laboratory experiment by adding 14C-labelled glucose and 14C-labelled maize shoots (maize) separately to a metal-contaminated and a non-contaminated soil from the field experiment. Microbial biomass C, ninhydrin-N, soil ATP content and CO 2 evolution were measured during the next 50 days following glucose addition and 100 days following maize addition in both soils. The biomass formed following addition of glucose or maize was consistently smaller in the metal-contaminated soil throughout the incubations. Overall, about 15–32% less glucose-derived and 25–60% less maize-derived biomass was formed in the metal-contaminated soil. In contrast, more CO 2-C was evolved from the metal-contaminated soil than from the non-contaminated soil. This suggests that the biomass in the metal-contaminated soil was less efficient in the utilisation of substrates for biomass synthesis. It is suggested that this may be a major reason lor the smaller biomass in the metal-contaminated Woburn soils.