Rhizodeposition and the Fate of Mineral-Associated Soil Carbon

Authors

Zoe Cardon¹* (zcardon@mbl.edu), Marco Keiluweit², Carolyn Malmstrom³, William Riley⁴, Mariela Garcia Arredondo⁵, Sherlynette Pérez Castro^1,6, Zelalem Mekonnen⁴, Suzanne Thomas¹, Kota Nakasato³, Jacob Gantz³, Ella Lemley-Fry⁷

Institutions

¹Marine Biological Laboratory, Woods Hole, MA; ²University of Lausanne, Switzerland; ³Michigan State University, East Lansing, MI; ⁴Lawrence Berkeley National Laboratory, Berkeley, CA; ⁵University of Massachusetts–Amherst, MA; ⁶University of Georgia, Athens, GA; ⁷Lawrence University, Appleton, WI

Abstract

Mineral-associated organic matter (MAOM) is a dominant component of total soil carbon (C). Once bound to reactive soil minerals that organic matter can be protected for millennia. Individual compounds commonly released by roots can mobilize MAOM off minerals to different extents, via different mechanisms, making the OM vulnerable to microbial attack. Carbon dioxide (CO₂) can then be released, and nutrients can be moved back into rapidly cycling pools, potentially creating a feedback to plant root activity. But rhizodeposits from living roots are complex mixes of compounds, and their quality and quantity vary with environmental conditions., Beyond demonstrating that individual compounds commonly lost by roots have the potential to mobilize MAOM, taking the next step requires exploring how naturally complex and dynamic mixes of rhizodeposits from live roots affect MAOM pool dynamics in soil. Researchers conducted two greenhouse growth chamber experiments quantifying the capacity of live root systems to mobilize MAOM off minerals as a function of altered morphology and physiology triggered by Barley Yellow Dwarf Virus (BYDV) infection, as a function of low soil nutrient and water availability. Among other results, respiration from soil under BYDV-infected plants had a higher percent ¹³C-MAOM-derived CO₂ (p = 0.001), and phosphorus and nitrogen limitation both could intensify MAOM mobilization and mineralization by plants. Researchers also explored the interaction of mycorrhizal and BYDV infection and developed an assay for visualizing (via fluorescence) the root-induced release of complex organic molecules from established associations with ferrihydrite. Researchers are currently using the model ecosys to explore the ecosystem-scale implications of altered kinetics of binding and release of OM to and from minerals, and altered capacity for OM binding, for C and nutrient cycling in grasslands and forests. Root-induced mobilization of MAOM has large potential to affect the productivity of ecosystems and the fate of large reserves of C stored in soil.