Microbial biomass and respiration in soils derived from lignite ashes: a profile study

Microbial biomass C and soil respiration measurements were made in 17-20 yr old soils developed on sluiced and tipped coal-combustion ashes. Topsoil (0-30 cm) and subsoil (30-100 cm) samples were collected from three soil profiles at two abandoned disposal sites located in the city area of Halle, Saxony-Anhalt. Selected soil physical (bulk density and texture) and chemical (pH, organic C, total N, CEC, plant available K and P, and total Cd and Cu) properties were measured. pH values were significantly lower while organic C and total N contents and the C : N ratio were significantly higher in the topsoil than in the subsoil indicating the effects of substrate weathering and pedogenic C accumulation. Likewise, microbial biomass C, K2SO4-extractable C, and soil respiration with median values of 786 mug biomass C g(-1), 262 mug K2SO4-C g(-1), and 6.05 mug CO2-C g(-1) h(-1), respectively, were significantly higher in the topsoil than in the subsoil. However, no significant difference was observed in metabolic quotient between the topsoil and the subsoil. Metabolic quotient with median values of 5.98 and 8.54 mg CO2-C (g biomass C)(-1) h(-1) for the 0-30 cm and 30-100 cm depths, respectively, was higher than the data reported in the literature for arable and forest soils. Microbial biomass C correlated significantly with extractable C but no relationship was observed between it and total N, Cd, and Cu contents, as well as plant-available K and R We conclude that the presence of the remarkable concentration of extractable C in the weathered lignite ashes allowed the establishment of microbial populations with high biomass. The high metabolic quotients observed might be attributed to the heavy-metal contamination and to the microbial communities specific to ash soils.