Biogenic weathering: opening the black box with new isotope systems and in situ mineral decomposition experiments (EarthShape – BioSoils)

Investigator Names and Contact Info:

• Friedhelm von Blanckenburg(Geochemistry, Cosmogenic Nuclides, Metal Stable Isotopes). German Research Centre for GeoSciences (GFZ) Potsdam, Germany
• Jens Boy. Leibniz Universität Hannover, Germany
• Georg Guggenberger. Leibniz Universität Hannover, Germany
• Robert Mikutta. Universität Halle, Germany

Chilean Collaborators Involved:

• Roberto Godoy (Biology, Chemistry). Instituto de Ciencias Ambientales & Evolutivas, Universidad Austral de Chile, Valdivia, Chile

Employ innovative isotope geochemical systems (metal stable, cosmogenic, radiogenic isotopes) to identify whether roots and associated fungi take up mineral nutrients and thus convert rock to soil by weathering.

PhD-Student:

• Ralf Oeser. GFZ Potsdam, Germany

Supervisor: Prof. Friedhelm von Blanckenburg, Co-supervisors: Dr. Jens Boy, Prof. Georg Guggenberger

Project Summary:

In EarthShape-BioSoils Isotope Geochemists will explore jointly with Soil Scientists and Environmental Ecologists whether biogenic weathering links denudation (removal of mass by erosion and solute transport) with soil production (supply of mass from rock). We hypothesise that biogenic weathering is controlled by nutrient demand of an ecosystems’ photoautotroph community in order to maintain the long-term nutritional status-quo. We focus on mycorrhizal fungi as the dominant weathering agents. At each of the EarthShape primary sites we will study biogenic weathering in two profiles, from the topsoil to the saprolite and, where possible, at the saprolite-bedrock boundary. We will employ innovative isotope geochemical systems (metal stable isotopes (26Mg/24Mg), radiogenic isotopes (87Sr/86Sr), cosmogenic nuclides (meteoric10Be/9Be)) in extracted soil profile compartments, water, and the prevalent vegetation to identify whether and from what depth roots and associated fungi take up mineral nutrients and thus convert rock to soil by weathering. We will futhermore characterise soil properties, including weathering and nutrient source-specific analyses; measuring potential biogenic weathering rates by mesocosm experiments and surface analytics of thin sections after recovery (CLSM, REM-EDS, XPS), and link these observations with chemical depletion budgets, erosion rate determination, and microbial characterisation by other EarthShape projects. The two time scales (biological time scales as recorded by mecocosm experiments and isotope ratios in higher plants and geological time scales as assessed by chemical depletion and isotope ratios in soil profiles) of our field experiments shall address the fundamental EarthShape hypothesis: biogenic processes adjust rapidly to environmental conditions, but their impacts are recorded in landscapes over geological time scales. The doctorate student will conduct field work in Chile and the isotope ratio work at GFZ Potsdam.