Munford, K. E. | Search bioRxiv

bioRxiv2026

Mineral dust stimulates microbial exoenzyme activity and enhances carbon mineralization capabilities in nutrient-poor peat soil

Nutrient limitation is an important control on heterotrophic microbial activity that helps to stabilize the massive stocks of organic carbon held in ombrotrophic peatlands. Minerals contained in atmospheric dusts are critical nutrient sources for peatlands, yet the role of dust in supporting the below-ground microbial processes that underpin primary productivity is largely unknown. We investigated how mineral dust generated from mining waste rock (<20 {micro}m) influences element bioavailability and subsurface microbial functioning using flow-through soil mesocosms. The bioavailability of base cations (Ca, Mg, K), transition metals (Fe, Al, Ni, Cu), Al, and P was tracked over two months at three soil depths (0-6, 6-12, and 12-18 cm) using an extended sequential extraction method. We also analyzed microbial community composition (16S rRNA and ITS amplicon sequencing) and mineralization capacity (exoenzyme assays and carbon substrate incubations). After two months, the concentration of metals in the peat increased substantially after dust application, but the mobility and bioavailability varied by element. Responses of microbial communities to dust application were highly dependent on depth from the surface. Carbon substrate incubations revealed enhanced mineralization capabilities in soil from the surface zone (0-6 cm), but a relatively low stimulation of exoenzymes. Soil pH and phosphorus mobility were also impacted near the site of dust application, while acid phosphatase activity was lower throughout the column. In the middle zone (6-12 cm), the activities of {beta}-glucosidase, {beta}-xylosidase, and NAGase were higher with dust exposure. Measured microbial activity mostly remained unchanged in the lowest depth (12-18 cm). We observed increases in the relative abundances of putative saprotrophic fungi throughout the mesocosm profile. Results from this experiment show that the deposition and weathering of mineral dust can induce a complex set of changes to the capacity and nature of microbial carbon mineralization within a shallow layer of peat.

ecology↗

bioRxiv2026

Tracking interlinked microbial and geochemical succession over decades in landfilled municipal solid waste

Landfills are heterogeneous built environments embedded in natural freshwater systems. They pose increasing risks of groundwater contamination from metal-bearing leachates over time. The interlinked succession of waste decomposition processes, microbial community membership and metal cycling across a landfills lifespan have not been explored, reducing our ability to predict the long-term environmental impacts of landfills. Working with 1,647 metagenome-assembled genomes from a single landfill, from samples spanning over 39 years of waste decomposition, we identified changes in landfill biogeochemistry and connected these changes to shifts in microbial community composition and predicted functions over time. Comparing between Older (aged 31 - 39 years) and Newer (aged 3 - 20 years) waste cells identified significant shifts in the availability of labile carbon, redox-associated processes, and concentrations of mobile metals - all higher in Newer cells. Newer cells were dominated by chemoorganoheterotrophs, while Older cells contained higher proportions of chemolithoautotrophs and organisms with higher metabolic versatility. Metal resistance and metal cycling genes were significantly more abundant in Older cells. Using geochemistry data from time of filling to present and microbial membership across six landfill cells of different ages, we developed a conceptual model of landfill characteristics across time. This model connects redox conditions and metal fate, highlighting leachate recirculation as a key process impacting many geochemical parameters and defining site chemistry. Our work highlights the substantial changes occurring over the stabilization phase and provides a conceptual framework for understanding this critical, final stage in a landfills life cycle. ImportanceAging landfills pose significant risks to environmental stability and are currently poorly modeled beyond [~]20 years. Our examination of a single landfill across 39 years of waste degradation was a unique opportunity to examine the impact of time within a connected system. Our work connects geochemical data, microbial membership and predicted function, as well as physical processes (e.g., leachate recirculation). Our conceptual model interlinks these facets across the lifespan of a landfill, providing an empirical data-based model of landfill aging. Previous models were extrapolated from younger waste and did not include the microbial dimension - a critical facet of the landfill ecosystem. Our model clarifies processes taking place in older wastes (30+ years), including oxygen infiltration, that have important implications for methane emission and metal mobility and fate over the longer-term.

microbiology↗