Advanced mine restoration protocols facilitate early recovery of soil microbial biomass, activity and functional diversity

Abstract

Many ecosystem restoration programmes can take over 15 years to achieve ecosystem functioning comparable to that of an unmodified ecosystem, therefore a reliable shorter-term method of assessing and monitoring ecosystem recovery is needed to ensure that recovery is following an appropriate trajectory. Soil microbes respond to environmental change relatively quickly, and shifts in microbial communities can reflect the current status of their environment. As well as potentially acting as ‘indicator communities’, microbes play an integral role in restoring ecosystem functions. On an active opencast mine on New Zealand's West Coast, three main restoration methods are used, differing in cost and restoration effort. They range from most expensive (1) vegetation direct transfer (VDT), to (2) biosolids-amended stockpiles that are spread and replanted, and (3) untreated stockpiles that are spread and replanted. We assessed the impacts of these methods on soil microbial communities by measuring microbial biomass, dehydrogenase activity, community level physiological profile (CLPP) and functional diversity as measured by carbon substrate utilisation, where restored sites were 5 years old or less. These measures were compared to an unmodified reference ecosystem in the same location. Microbial activity and biomass were highest in pristine habitats, followed by VDT and biosolids-amended soils, then untreated stockpile soil. When compared to all other treatments untreated stockpiled soils had significantly different CLPPs and significantly reduced microbial biomass and activity; microbial biomass was an order of magnitude lower than in pristine soils. Functional diversity and richness did not differ between pristine, VDT and biosolids-amended soils, but were higher than in untreated stockpiled soils. CLPPs did not differ between pristine habitat soil and VDT soil but biosolids-amended and untreated stockpiled soils were significantly different to pristine soil. This study has shown that soil microbial communities are a valuable tool to assess restoration progress, and that ecosystem restoration can begin in a relatively short time following investment in appropriate restoration strategy, ultimately benefiting recolonisation by plants and animals.