Microbial Weathering Effects on Early Landscape Evolution in a Deglaciated Alpine Basin

Microorganisms contribute to surface processes through the physical and chemical weathering of minerals, yet their influence on landscape evolution remains difficult to quantify. Recently deglaciated landforms provide a natural laboratory to examine early-stage interactions, as freshly exposed surfaces become available to microbial community establishment and rock-to-soil weathering. Here, we compare microbial community composition and potential weathering capacity across a weathering gradient from bare bedrock to saprolite and soil, using DNA-based sequencing (16S rRNA). Sampling in a recently deglaciated basin (~13 ka) in the eastern Sierra Nevada, California, we find that microbial communities in soil and saprolite exhibit higher diversity and an order-of-magnitude enrichment of weathering-related metabolic pathways. In contrast, bedrock communities remain low-diversity and compositionally similar to those reported from newly deglaciated surfaces worldwide, even after ~13 kyr of exposure. These results indicate that microbial communities diverge along two distinct ecological trajectories: in soil-mantled surfaces, microbially mediated feedbacks enhance soil production and surface transformation, while rock surfaces remain effectively locked in low-weathering conditions and ecological stasis over millennial timescales. Together, these findings demonstrate that microbial lifeforms can influence early stages of landscape evolution in recently deglaciated terrains.