4.8 Article

A New Method to Capture the Spatial and Temporal Heterogeneity of Aquatic Plant Iron Root Plaque In Situ

Journal

ENVIRONMENTAL SCIENCE & TECHNOLOGY
Volume 55, Issue 2, Pages 912-918

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acs.est.0c02949

Keywords

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Funding

  1. University of Delaware
  2. Brookhaven National Laboratory
  3. U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-76SF00515]
  4. DOE Office of Science [DESC0012704]

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The study demonstrates that the oxygen released by aquatic plant roots forms reduced metal plaques on the root surface, which are important for microorganisms and biogeochemical cycling. A new nondestructive and repeated rhizosphere sampling technique was introduced for studying the biogeochemical characteristics of aquatic plant roots.
The roots of aquatic plants, including rice, release oxygen into the subsurface, precipitating reduced metals, such as iron (Fe) and manganese (Mn), as plaques that form on the surface of the roots. These plaques are a unique habitat for microorganisms and a hotspot for biogeochemical cycling, including the toxic trace metalloid arsenic (As). However, studying plaque deposition and mineral composition in this spatially and temporally heterogeneous environment is challenging, particularly in situ. Here, we describe a new technique for nondestructive and repeated rhizosphere sampling. We placed vinyl films that adhere Fe deposits from roots growing adjacent to the films into soil. The films were removed and replaced throughout plant growth and were characterized using a variety of spectroscopic (XRF imaging and Fe EXAFS) and microscopic (SEM and confocal) techniques. Fe deposits were most concentrated at lateral junctions and heterogeneity was apparent in the location and speciation of Fe-associated As in both pot and field studies. XRF imaging at multiple incident beam energies revealed that this As was mostly arsenate, although arsenite was present on the edge of the Fe deposit. Iron deposits were typically micron sized and consisted mostly of ferrihydrite, consistent with the data reported using conventional techniques. Moreover, Fe deposits were occupied by a variety of microorganisms. These films are a suitable technique to study a range of spatial and temporal questions regarding the biogeochemistry of aquatic plant roots.

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