Bacterial and Eukaryotic Communities within and Beneath New Rooting Zones of Incipient Soils Formed From Acid Mine Drainage Precipitates Amended with Compost.

In mining areas throughout the world, overland flow of acid mine drainage (AMD) causes iron oxy(hydr)oxides to precipitate and accumulate on native soils, killing vegetation and creating AMD barrens. Once AMD flow is stopped or diverted, these dead areas contribute to downstream pollution for decades if vegetation is not established to initiate soil formation. The impact of reclamation on bacterial and eukaryal taxa was investigated in iron-rich precipitates at a 50-year-old AMD barrens in Central Pennsylvania. Lime and compost (11 and 27 ton ha^-1, respectively) were roto-tilled into the upper 15 cm of the precipitate layer, which was mulched with oat straw (9 ton ha^-1) that provided a first-year nurse crop of oats. Plants from the sown “reclamation seed mix” that germinated in the second year were replaced by diverse indigenous species. We hypothesized that after six growing seasons, amended precipitates would support increased microbial diversity and more mycorrhizal fungi compared to precipitates from non-amended areas supporting biological crusts. We also expected a shift from iron-oxidizing lithoautotrophs to heterotrophs when going from non-reclaimed to reclaimed precipitates. DNA was extracted (MoBio PowerLyzer Soil kit) from four types of precipitates: root-adhering; root-non-adhering; crust-adhering; and crust-non-adhering. We employed barcoded GS FLX pyrosequencing of 16S rRNA and 18S rRNA, the MOTHUR pipeline, and SILVA database to assess differences in phylotypes. Amended plots had higher organic carbon than non-amended plots but similar contents in root-adhering (2.7%) and root-non-adhering precipitates (2.4%). More stratified distribution of organic carbon was observed in crust-adhering (1.75%) and crust-non-adhering (0.65%) precipitates in non-amended plots. In contrast, pH values were similar (2.5 to 2.7) among all four sample types. Electrical conductivities were generally low, ranging from 1.0 to 1.8 dS m^-1. This study sheds light on how microbial communities respond to compost amendments in reclaimed AMD areas during soil development.