ETBC: Plant-microbe-mineral interaction as a driver for rock weathering and chemical denudation

University Of Arizona, Tucson AZ

Investigators

Abstract

Plants and microorganisms modify the local weathering environment by exuding organic compounds, CO2 and protons, altering the composition of geomedia surfaces, redirecting soilwater and solute fluxes, and immobilizing lithogenic nutrients. The goal of this study is to better understand the effects of plants on weathering and denudation. The PIs propose to measure how plant-microbe interactions affect the initial weathering of four distinct rock types (basalt, granite, schist, and rhyolite) and the extent to which this weathering results in chemical denudation versus biomass accumulation or re-precipitation of dissolution products. Two types of higher plants will be used in a replicated plant-microbe-rock mesocosms experiment: a grass species (with vesicular arbuscular mycorrhizal association) and a tree species (with ectomycorrhizal association). The experiments will also include plant-free (but microbially-colonized) and abiotic (sterile) controls. One hypothesis is that the presence of plants will increase weathering but decrease denudation (i.e., we will see more mineral transformation but less element loss from system in the presence versus absence of plants). This implies important feedbacks to soil fertility and C sequestration. A series of environmentally-controlled, greenhouse experiments will be conducted that involve measuring plant uptake, mineral transformation and chemical denudation in basalt, granite, rhyolite, and schist, as affected by presence and growth of microbiota and vascular plants. Weathering will be estimated based on denudation, bio-uptake, sorption, and secondary mineral precipitation, each of which will be quantified by detailed characterization of biomass, aqueous solution and effluxes, and solid phase changes. Experimental results will be used to parameterize a biogeochemical model. Broader Impacts: This project will enable the training of two collaborating Ph.D. students whose thesis research will focus on the vibrant interface between biogeochemistry, microbial ecology, and plant physiological ecology. Research will be closely coordinated with broader efforts associated with the National Critical Zone Observatory (CZO) system, and also with Biosphere2 (B2), a unique research instrument now managed by the University of Arizona. Conceptual and practical linkages with B2 and CZO will place the well-controlled experiments into a broader context of parallel field and "macrocosm" studies that are unable to address these questions unambiguously. Interaction with B2 and CZO will also create a collaborative environment where the Ph.D. students will be required to integrate their mechanistic findings into an evolving understanding manifested at larger (pedon to hillslope to catchment) scales. B2, which has fifty thousand visitors a year, will provide a compelling environment and powerful venue for research translation to the general public.