Abstract
To improve our understanding of early microbial colonization of pristine minerals and their group-specific C utilization, we exposed minerals (illite/goethite/quartz) amended with artificial root exudates (ARE, glucose, and citric acid) in grassland soils for a period of 24 weeks. FTIR spectra indicated that mineral-associated ARE were used within the first 2 weeks of exposure and were replaced by other carbohydrates derived from living or dead cells as well as soil-borne C sources transported into the mineralosphere after heavy rain events. Fungi and Gram-positive bacteria incorporated ARE-derived C more rapidly than Gram-negative bacteria. Gram-negative bacteria presumably profited indirectly from the ARE by cross-feeding on mineral-associated necromass of fungi and Gram-positive bacteria. The Gram-negative bacterial phyla Verrucomicrobia, Planctomycetes, Gemmatimonadetes, Armatimonadetes, and Chloroflexi showed a positive correlation with Gram-negative PLFA abundances. After 24 weeks of exposure in the grassland soils, abundances of soil microorganisms in the mineralosphere reached only 3.1% of the population density in soil. In conclusion, both bacteria and fungi slowly colonize new surfaces such as pristine minerals, but quickly assimilate artificial root exudates, creating an active microbial community in the mineralosphere.
Highlights
The survival and functioning of soil microorganisms in terrestrial ecosystems depend on interactions between biotic andBiol Fertil Soils (2021) 57:587–601 different minerals (Sun et al 2020), and the decomposition of mineral-associated organic matter (Chenu and Stotzky 2002; Wang et al 2019)
These spectra corresponded to 54.7 μg of AREderived C associated with the pristine minerals
We assume that different substrate sources, ARE-derived glucose and citric acid, microbially processed ARE, as well as soil-derived polysaccharides, polysaccharide-like compounds, and other complex C compounds were used by microorganisms in the mineralosphere over the longer exposure time of the mineral containers
Summary
The survival and functioning of soil microorganisms in terrestrial ecosystems depend on interactions between biotic andBiol Fertil Soils (2021) 57:587–601 different minerals (Sun et al 2020), and the decomposition of mineral-associated organic matter (Chenu and Stotzky 2002; Wang et al 2019). The types of minerals and the amount and composition of organic substrates play important roles in the abilities of different soil microorganisms to colonize the mineralosphere. The most labile C components in rhizodeposition are root exudates (Grayston et al 1997), which consist predominantly of sugars, amino acids, and organic acids (van Hees et al 2005). They are known to increase soil microbial activity and abundance and to affect microbial community composition (Grayston et al 1997; Rovira 1969; Strickland et al 2015; Vieira et al 2020). Any organic compound entering the mineralosphere may be either directly bound to pristine minerals or first processed by microorganisms with subsequent adsorption to mineral surfaces
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