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• Research into treatment of fine-textured soils with biomass bottom ash is lacking. • Ash self-hardening improves handling but changes ash chemistry. • Ash hardening alters mobility of plant nutrients and trace elements of concern. • Adding ash to soil decreases mobility of most but not all trace elements of concern. • Bottom ash addition can provide safe, value-added benefit to fine-textured soil. Biomass ashes are potential soil amendments that reduce soil acidity and provide plant nutrients, but trace elements in ash may be leached from the solid phase, thereby posing environmental concerns. We determined the leachability of selected major elements, trace elements and anions from wood derived bottom ash generated from an updraft gasifier as influenced by ash pretreatments and the presence of soil via serial aqueous batch extraction. We found that self-hardening reduced initial solubility and reactivity of ash (i.e. lowered electrical conductivity), and reduced initial aqueous concentrations of Ba, Ca, Cu, Fe, Hg, Pb, Sr and Zn. But, hardening of ash increased initial aqueous concentrations of B, Cr, P, Se and SO 4 2−. Although mixing ash into soil (5% ash by mass) generally decreased the mobility of most constituents, aqueous concentrations of P and As were increased relative to that of either ash-alone or soil-alone treatments. Overall, extract concentrations of constituents in various treatments were relatively low. Results of this serial batch extraction support the use of clean wood-derived bottom ash as a safe and environmentally suitable soil amendment. [ABSTRACT FROM AUTHOR]

Highlights • Soil rehabilitation treatments increased bacterial saprotroph abundance 14 days after implementation. • Rehabilitation treatments showed strong fungal saprotroph abundance 5 months after implementation. • Ectomycorrhizal mycelia were a major necromass input due to soil manipulation. • Several microbial genera stimulated by rehabilitation treatments are previously described as mycelial decomposers. Abstract The replacement of mineral soil and capping with salvaged forest floor organic material (FFOM) is a site rehabilitation method applied over belowground installations such as pipelines. Such installations, when placed in mature forest soils, can be expected to disrupt ectomycorrhizal fungal communities when root-associated mycelia and exploratory hyphae are damaged during excavation. Soil fungal communities, bacterial communities, and soil enzymatic repertoires may be variably impacted by different site preparation schemes after disturbance. We compared effects of three rehabilitation schemes on fungal community composition, bacterial community composition, and potential hydrolase activities (N -acetyl-β- d -glucosaminidase, acid phosphatase, and cellobiohydrolase) at two times (14 days and 5 months post-site preparation) and two sampling depths (FFOM/"upper" versus mineral/"lower" soil). We observed declines in FFOM-associated fungal biomass (ergosterol) and declines in ectomycorrhizal fungi abundance across all site rehabilitation schemes compared to intact control plots. Fungal community composition strongly shifted to saprotroph dominance (i.e. increased Mortierella , and Umbelopsis) in rehabilitated plots at 5 months, while bacterial community composition did not distinguish control plots from rehabilitation plots ones at either sampling time. Bacterial saprotrophs previously associated with mycelial necromass colonization were higher in abundance across multiple site preparation regimens compared to control plots at 14 days. Our results indicate that reductions in ectomycorrhizal fungal abundance were a dominant community property in recently reconstructed soil profiles. Increases in bacteria associated with recently deposited fungal necromass were detectable within days to weeks of implementing site rehabilitation, while fungal necromass colonizers became dominant 5 months post-rehabilitation. Potential hydrolase activities increased in the site preparation regimen where FFOM was mixed into mineral soil, when compared to mineral soil activities in control plots. [ABSTRACT FROM AUTHOR]

Physical disturbance of soil profiles, even at shallow depths, is a ubiquitous consequence of anthropogenic landscape modification, with short-term impacts on important ecological guilds of fungi. DNA-based methods for surveying community composition are widely incorporated into studies attempting to explain fungal responses to forest ecosystem disturbances. Here we compare fungal community composition between three distinct soil profile manipulations (20 cm depth) and undisturbed control plots in a sub-boreal spruce forest in the Central Interior region of British Columbia, Canada. Fungal community composition differences were tracked by internal transcribed spacer 2 (ITS2) amplicon sequencing, with comparisons drawn using genus-level annotations. Non-metric multidimensional scaling (NMDS) analysis indicated that disturbed-sample community compositions were similar to controls at 0-months and distinct from controls at 5- and 12-months post disturbance, but did not indicate clustering of samples according to disturbance regime. We used Linear Discriminant Effect Size (LEfSe) analysis to identify fungal genera that consistently indicate disturbed or undisturbed (control) treatments across 5- and 12-month sampling times. Four fungal genera ( Exophiala , Hyphodontiella , Mastigobasidium , and Umbelopsis ) were detected with higher ranges of relative abundance in all disturbance regimes when compared to control plots. Deliberate mixing of LFH into mineral horizon soils stimulated multiple genera that were more frequently detectable in replicate plots at 12 months, when compared to undisturbed and immediately re-assembled plots. Four ectomycorrhizal genera ( Amphinema , Cortinarius , Piloderma , and Russula ) were identified as strong indicators of control plot soils. A single genus, Capronia , was identified as differentially abundant between stockpiled LFH and immediately replaced LFH. Our results are consistent with declines in ectomycorrhizal fungal abundance and increases in saprotroph abundance previously reported in DNA-based community profiling studies of forest soil disturbance. This investigation demonstrates that bulk soil sampling can be used to evaluate soil-handling regimens to understand fungal community disruption/recovery and highlights LEfSe as an approach to indicator selection in DNA-dependent biodiversity surveys. [ABSTRACT FROM AUTHOR]