Development of soil microbial properties in topsoil layer during spontaneous succession in heaps after brown coal mining in relation to humus microstructure development

A wide spectrum of soil microbial parameters (microbial biomass, respiration, direct counts of bacteria, fungal mycelium length, cellulose decomposition and FDA activity) was studied in the chronosequence of 1- to 41-year-old plots of spontaneous succession on post-mining sites near the town of Sokolov. At these sites, soil chemical properties and the role of humus micromorphology (driven by soil fauna activity) were recorded, and their relation to changes in microbial properties was evaluated. Growth of herbs and grasses occurred only occasionally on 3- to 14-year-old plots. Shrubs (Salix caprea) covered a plot 15-25 years old, and 26- to 41-year-old plots were forested mainly with Populus tremuloides and Betula spp. Organic matter content increased, while pH decreased during succession. Organic matter accumulation seems to be the main factor affecting the development of the soil microbial community. All investigated parameters, with the exception of mycelium length, correlated positively with soil organic carbon. Most of the parameters measured at 30- to 40-year-old forested sites were of comparable magnitude to undisturbed habitats. Respiration per unit of microbial biomass (metabolic quotient) decreased with increasing succession age. The microbial community was strongly affected by humus form created by the activity of soil invertebrates. A rapid increase in all microbial parameters, again with the exception of mycelium length, was observed when moder developed under shrub cover. A shift from moder, typical of intermediate succession stages, to mull in later succession stages was accompanied by an increase in bacterial numbers and a decrease in microbial biomass, respiration and FDA. These changes correspond to: (i) a decrease in organic carbon content in topsoil layer, caused by earthworm-mediated soil mixing and (ii) a decrease in the availability of soil organic matter.