Root-driven weathering impacts on mineral-organic associations in deep soils over pedogenic time scales
AuthorGarcia Arredondo, Mariela
Lawrence, Corey R.
Schulz, Marjorie S.
Tfaily, Malak M.
Jones, Morris E.
AffiliationUniv Arizona, Soil Water & Environm Sci Dept
Soil organic matter
Short-range order minerals
MetadataShow full item record
PublisherPERGAMON-ELSEVIER SCIENCE LTD
CitationArredondo, M. G., Lawrence, C. R., Schulz, M. S., Tfaily, M. M., Kukkadapu, R., Jones, M. E., ... & Keiluweit, M. (2019). Root-driven weathering impacts on mineral-organic associations in deep soils over pedogenic time scales. Geochimica et Cosmochimica Acta, 263, 68-84.
JournalGEOCHIMICA ET COSMOCHIMICA ACTA
Rights© 2019 Elsevier Ltd. All rights reserved.
Collection InformationThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at email@example.com.
AbstractPlant roots are critical weathering agents in deep soils, yet the impact of resulting mineral transformations on the vast deep soil carbon (C) reservoir are largely unknown. Root-driven weathering of primary minerals may cause the formation of reactive secondary minerals, which protect mineral-organic associations (MOAs) for centuries or millennia. Conversely, root-driven weathering may also transform secondary minerals, potentially enhancing the bioavailability of C previously protected in MOAs. Here we examined the impact of root-driven weathering on MOAs and their capacity to store C over pedogenic time scales. To accomplish this, we examined deep horizons (100-160 cm) that experienced root-driven weathering in four soils of increasing ages (65-226 kyr) of the Santa Cruz marine terrace chronosequence. Specifically, we compared discrete rhizosphere zones subject to root-driven weathering, with adjacent zones that experienced no root growth. Using a combination of radiocarbon, mass spectrometry, Fe-57 Mossbauer spectroscopy, high-resolution mass spectrometry, and X-ray spectromicroscopy approaches, we characterized transformations of MOAs in relation to changes in C content, Delta C-14 values, and chemistry across the chronosequence. We found that the onset of root-driven weathering (65-90 kyr) increased the amount of C associated with poorly crystalline iron (Fe) and aluminum (Al) phases, particularly highly disordered nano-particulate goethite (np-goethite). This increase coincided with greater C concentrations, lower Delta C-14 values, and greater abundance of what is likely microbially-derived C. Continued root-driven weathering (137-226 kyr) did not significantly change the amount of C associated with crystalline Fe and Al phases, but resulted in a decline in the amount of C associated with poorly crystalline Fe and Al phases. This decline coincided with a decrease in C concentrations, an increase in Delta C-14 values, and a shift toward plant-derived C. In contrast, soil not affected by root-driven weathering showed comparatively low amounts of C bound to poorly crystalline Fe and Al phases regardless of soil age and, correspondingly, lower C concentrations. Our results demonstrate that root-driven formation and disruption of MOAs are direct controls on both C accrual and loss in deep soil. This finding suggests that root impacts on soil C storage are dependent on soil weathering stage, a consideration that is critical for future predictions of the vulnerability of deep soil C to global change.
Note24 month embargo; available online 23 July 2019
VersionFinal accepted manuscript
SponsorsNational Science Foundation Graduate Research Fellowship ProgramNational Science Foundation (NSF); SLAC SFA research program - U.S. Department of Energy (DOE) Subsurface Biogeochemical Research (SBR) program within the Office of Biological and Environmental ResearchUnited States Department of Energy (DOE) [SLAC FWP 10094]; U.S. Geological Survey Land Change Science Program; Canada Foundation for InnovationCanada Foundation for Innovation; Natural Sciences and Engineering Research Council of CanadaNatural Sciences and Engineering Research Council of Canada; University of Saskatchewan; Government of Saskatchewan; Western Economic Diversification Canada; National Research Council Canada; Canadian Institutes of Health ResearchCanadian Institutes of Health Research (CIHR); Office of Biological and Environmental Research; DOE, Office of Biological and Environmental Research, SBR programUnited States Department of Energy (DOE) [DE-SC0019477]