277-1 Microbial Succession as a Driver of Early Landscape Evolution in a Deglaciated Alpine Basin

Session: Critical Zone Science: Intersection of Processes Linked to Geomorphology, Ecology, Fire and Climate

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Abstract:

Microorganisms play a central role in shaping Earth’s surface through weathering and soil formation, yet their long-term interactions with geomorphic processes remain poorly understood. We investigate microbial succession and its potential feedbacks with surface processes in a recently deglaciated alpine basin in the eastern Sierra Nevada. Combining 16S rRNA gene sequencing with cosmogenic 10Be surface exposure dating, we assess microbial community composition across a weathering gradient from bare bedrock to saprolite and soil.

Our results show that microbial communities diverge along two distinct trajectories: in soil-mantled environments, microbial diversity and functional potential increase with weathering intensity, consistent with a positive feedback loop where microbially mediated weathering promotes soil development and increasingly favorable habitat conditions. In contrast, exposed bedrock communities remain low-diversity and compositionally similar to early colonizers even after ~13,000 years, with minimal evidence of ecological or geomorphic change.

Functional predictions suggest a tenfold enrichment of weathering-related metabolic pathways in soil and saprolite relative to surface rock. Strikingly, surface rock communities more closely resemble those on newly deglaciated surfaces worldwide than adjacent soils only meters away, suggesting ecological stasis. Together, these findings reveal how microbial diversity and functional capacity can amplify initial geomorphic change, or fail to initiate it. This work highlights the underappreciated role of microbial communities in driving the earliest stages of soil formation and contributes to a growing understanding of life-landscape interactions in the critical zone.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9454

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