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Arredondo, Mariela Garcia

MS/Ph.D., Eco


Understanding how plant development and root weathering induces priming mechanisms that impact mineral-organic associations, which mobilize iron and carbon in the process.



Faculty Advisor:

Marco Keiluweit


Project Abstract:

Plant roots reshape the soil environment by releasing approximately 25-40% of their photosynthetically fixed carbon (C) as root-derived compounds. While root-derived organic compounds are recognized as an important source of soil C, their role in promoting weathering reactions has been overlooked. Root-driven weathering may generate mineral-organic associations, which protect up to 91% of deep soil C for centuries to millennia. In contrast, root-driven weathering may also cause mineral transformations, potentially disrupting mineral-organic associations. Hence root-derived C may not only initiate C accumulation in deep soils, but also diminish C stocks through disruption of mineral-organic associations. Yet, the cumulative impact of root-driven weathering on mineral-organic associations is largely unknown. Therefore, our overarching goal was to examine root-promoted transformations of mineral-organic associations, and related changes in C storage, in deep soil. To accomplish this goal, we examined root impacts on soil C residence time and chemistry, mineralogy and mineral-organic associations across the Santa Cruz Marine Terrace chronosequence (65ka-226ka). As soils aged, and rhizogenic weathering increased, we observed a gradual change from predominantly root-derived to microbially-derived organic matter via mass spectrometry. Mössbauer and sequential extractions showed amorphous Fe (and Al) complexes formed during initial weathering, whereas crystalline (hydr)oxides dominated later weathering stages. X-ray spectro-microscopy revealed strong spatial associations between C and Fe during initial weathering stages, indicative of protective mineral-organic associations. In contrast, later weathering stages showed weaker spatial relationships between C and Fe. We conclude that initial root-induced weathering creates metal-organic complexes, protecting root-derived C from decay. As root-driven weathering proceeds, minerals transform into more crystalline phases that retain lower amounts of microbially-derived C. Our results suggest that root-induced weathering reactions are primary drivers of the formation and disruption of mineral-organic associations, and are thus critical for future predictions of the vulnerability of deep soil carbon to climate change impacts.



NEAGAP Scholar 2016
 NSF Graduate Research Fellowship Program Recipient

Page updated: October 2, 2017