Particulate organic carbon at reclaimed and unreclaimed post-mining soils and its microbial community composition

Abstract

Recovery of soil organic matter and associated microbial biomass is a fundamental precondition for successful restoration of post-mining soils. The aim is to compare the dynamics of soil C fractions and of microbial communities associated with these fractions in two chronosequences of post-mining sites with different plant communities. Soil carbon, pH, bulk density and the light fraction of particulate organic carbon (POC), free or bound in soil aggregates, were studied along two chronosequences, both covering successional ages from 10 to 50years. One chronosequence had been reclaimed by planting of alder, while the other had been vegetated by natural regrowth (Salix caprea, Populus tremula and Betula pendula). In intermediate and late successional stages, microbial community in bulk soil and POC fractions were studied using phospholipid fatty acid analysis. Soil C content increased and pH decreased with plot age, these trends being more pronounced at reclaimed sites. The light and bound POC fractions increased with age, higher values and a larger increase being found at reclaimed sites. In both chronosequences, the light fraction was an order of magnitude higher than the bound fraction. C content in both fractions increased with successional age, with higher C content at reclaimed sites. Microbial communities were more affected by the POC fraction than plot age. The bulk soil of reclaimed sites was more similar to bound POC, while the bulk soil of unreclaimed soils was similar to the light POC fraction. Observed differences correspond with a higher level of bioturbation at the reclaimed sites, which promotes faster accumulation of bound POC and drives bulk soil microbial communities closer to those of bound POC.