MICROBES IN THE WEATHERING ENVIRONMENT

Microorganisms play an important role in weathering processes, influencing soil formation, water chemistry and regulating nutrient uptake of plants by modifying their environment to make it habitable. This presentation summarizes several collaborative studies that focused on understanding processes at the plant-microbe-mineral interface and investigated the role of biofilm and direct mineral surface contact of microbes in mineral weathering. The associations between the plants and microbes regulate several mechanisms where the plants provide the photosynthetic energy driving the weathering processes that result in nutrient release for immediate needs of the plants and microorganisms, and precipitation of secondary phases that provide sinks for unwanted elements and surfaces for nutrient accumulation. It is challenging to determine the contributions of plants and microorganisms (such as bacteria and fungi) to mineral weathering, because they interact intimately within rhizospheric biofilms, enhancing, reducing and amplifying each other’s actions. To be able to address multiple processes that contribute to and result from microbial weathering, a combination of chemical, biological, mineralogical, and computational techniques and methodologies is needed. We employed a variety of methods ranging from bulk to surface-specific techniques, such as 1) estimation of lithogenic elements weathered using amounts of cations in drainage and soil waters; plant biomass and soil exchangeable sites determined by inductively coupled plasma atomic emission spectroscopy; and 2) characterization of mineral surface changes, microbial attachment structures and biofilm covers using several scanning and transmission electron microscopy and atomic force microscopy methods. These techniques in combination with tracer studies, molecular microbiology methods and numerical geochemical modeling are being employed to improve our understanding of microbial weathering.