Abstract
Secondary minerals (clays and metal oxides) are important components of the soil matrix. Clay minerals affect soil carbon persistence and cycling, and they also select for distinct microbial communities. Here we show that soil mineral assemblages—particularly short-range order minerals—affect both bacterial community composition and taxon-specific growth. Three soils with different parent material and presence of short-range order minerals were collected from ecosystems with similar vegetation and climate. These three soils were provided with 18O-labeled water and incubated with or without artificial root exudates or pine needle litter. Quantitative stable isotope probing was used to determine taxon-specific growth. We found that the growth of bacteria varied among soils of different mineral assemblages but found the trend of growth suppression in the presence of short-range order minerals. Relative growth of bacteria declined with increasing concentration of short-range order minerals between 25–36% of taxa present in all soils. Carbon addition in the form of plant litter or root exudates weakly affected relative growth of taxa (p = 0.09) compared to the soil type (p < 0.01). However, both exudate and litter carbon stimulated growth for at least 34% of families in the soils with the most and least short-range order minerals. In the intermediate short-range order soil, fresh carbon reduced growth for more bacterial families than were stimulated. These results highlight how bacterial-mineral-substrate interactions are critical to soil organic carbon processing, and how growth variation in bacterial taxa in these interactions may contribute to soil carbon persistence and loss.
Highlights
Soil microbial activity is responsible for one of the largest fluxes in the terrestrial carbon (C) cycle
Denoised sequences were clustered into amplicon sequence variants (ASVs) at 100% sequence identity and taxonomy was assigned using the q2-feature-classifier, classify-sklearn naïve rates after one week of incubation compared to the granite soil (Table 1)
Fresh C substrate increased total CO2–C respired from all soils, with exudate addition eliciting greater CO2–C respired than litter addition
Summary
Soil microbial activity is responsible for one of the largest fluxes in the terrestrial carbon (C) cycle This activity comes from an immensely diverse collection of co-existing organisms from all branches of the tree of life, with a single gram of soil often containing more than a billion organisms and thousands of species [1]. This biological diversity arises in part from physical and chemical complexity of the soil environment which includes a diverse soil mineral matrix. Clay particles can protect bacteria from predation and unfavorable climatic conditions [2], yet can limit growth by restricting microbial mobility [23] as well as access to organic matter (OM) [8]
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