B105-02
The Fate of Mineral-Organic Associations Within Functionally Distinct Rhizosphere Microenvironments

Tuesday, 15 December 2020: 19:04
Virtual
Mariela Garcia Arredondo1, Zoe G Cardon2, Morris E Jones1, Rene Boiteau3, Yilin Fang4, Rosalie Kae Chu5, Steven Yabusaki6 and Marco Keiluweit1, (1)University of Massachusetts Amherst, Amherst, MA, United States, (2)Marine Biological Laboratory, Ecosystems Center, Woods Hole, MA, United States, (3)Oregon State University, Corvallis, OR, United States, (4)Battelle, Pacific Northwest National Laboratory, Richland, WA, United States, (5)Pacific Northwest National Laboratory, Environmental Molecular Sciences Laboratory, Richland, WA, United States, (6)Pacific Northwest National Laboratory, Richland, WA, United States
Recorded Presentation
Abstract:
Understanding the dynamics and vulnerability of mineral-organic interactions is critical for projecting climate change impacts on soil fertility and carbon storage. Plant roots and associated microbes release an array of reactive rhizodeposits, potentially both forming and disrupting protective mineral-organic associations (MOAs) in the surrounding soil. But our ability to measure and predict the impact of rhizodeposits on the dynamics of MOAs in the rhizosphere remains limited. Here, we used an integrated experiment-modeling approach to assess the fate of MOAs within dynamic, biogeochemically distinct microenvironments in the rhizosphere. We combined in-situ micro(bio)sensors, mass spectrometry and reactive transport modeling to follow the impact of single roots on the dynamics of protective iron (Fe)-organic matter associations.

Continuous, high-resolution micro(bio)sensor measurements of growing and maturing Avena sativa roots revealed diel cycles with dramatic changes along transects, from root tip, to uptake zone, and mature suberized zones. Root tips showed a sharp decline in pH and redox potential as well as a concurrent increase in microbial activity, Fe and DOC concentrations. As roots matured, microbial activity decreased while pH and redox potential recovered followed by a decline in Fe and DOC concentrations. Metabolite analysis via tandem mass spectrometry (LC-FT-ICR-MS) shows a progression of functionally distinct rhizodeposits such as organic acids, amino acids, and lipids from root tips to more mature zones. Modeling confirms that these dynamic changes in rhizosphere biogeochemistry are sufficient for repeated reductive dissolution and re-precipitation of Fe oxides, causing the disruption and neoformation of protective Fe-organic matter associations.

Our results suggest that the fate of MOAs in the rhizosphere depends, in part, on the distinct nature of transient microenvironments emerging around different root segments. Our integrated experiment-modeling approach provides the unique ability to systematically assess the dynamic interplay between roots, microbes and minerals within these microenvironments, and elucidate their sensitivity to shifts in climate and vegetation which are fundamental to predictions of soil fertility and carbon storage.

<< Previous Abstract | Next Abstract >>