Biological Weathering, Scale and the Brush of Picasso.

Ecosystem - bedrock interactions power the biogeochemical cycles of Earth’s shallow crustal environment supporting life, fueling surface transformations and stimulating biological innovation at a variety of scales. While mineral weathering sits at the core of such transformation, our current picture of the relative contribution of different abiotic and biotic components, and how these propagate across scales is still broadly outlined. Here I will present our recent work on incipient biological weathering, with a focus on micron-to-plant scales, and connect it to ecosystem - landscape interactions at relevant macroscales.

Major elements mobilization in a biological weathering system, measured using column experiments experienced an initial high flux of elements from open mineral lattices which lasted 3-4 months, followed by a lower, but steady release over time. Element fractional distribution was rock specific and followed the order: poorly - crystalline > exchangeable forms > dissolved ions > plant biomass. Compared to abiotic weathering, the biotic component accelerated CO₂ mineralization pathways with increasing ecosystem complexity (microbes, microbes-plant, microbes-plant-arbuscular mycorrhiza), and modified element stoichiometry in the mobilized fractions. Weathering variability among rocks and differences in element partitioning under the effect of biota resulted in variable element allocation to water, secondary solids and plant organs.

The emergence of macroscale (ecotope, catchment and mountain range) patterns in a young alpine riparian ecosystem characterized by high weathering was bedrock specific, and was contingent on variables associated to hydrodynamics, topography and geomorphology. Moreover, plant species composition responded to pan-climatic gradients altitude and latitude, which captured in a narrow geographic area the transition between large climatic zones. A cohesive understanding of biosphere - geosphere - hydrosphere - atmosphere coupling at its full range of scales is critical for improving Earth system evolution models, it can inform a more sustainable human development, and can provide unprecedented tools in the search of biosignatures elsewhere.