The ratio of germanium to silicon in plant phytoliths: quantification of biological discrimination under controlled experimental conditions |
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Authors: | Steve W Blecker Stagg L King Louis A Derry Oliver A Chadwick James A Ippolito Eugene F Kelly |
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Institution: | (1) Department of Forest Resources, University of Idaho, Moscow, ID 83844, USA;(2) Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, NY, USA;(3) Department of Geography, University of California Santa Barbara, Santa Barbara, CA, USA;(4) Department of Soil and Crop Sciences, Colorado State University, Fort Collins, CO, USA |
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Abstract: | Slight differences in the chemical behavior of germanium (Ge) and silicon (Si) during soil weathering enable Ge/Si ratios
to be used as a tracer of Si pathways. Mineral weathering and biogenic silicon cycling are the primary modifiers of Ge/Si
ratios, but knowledge of the biogenic cycling component is based on relatively few studies. We conducted two sets of greenhouse
experiments in order to better quantify the range and variability in Ge discrimination by plants. Graminoid species commonly
found in North American grassland systems, Agropyron smithii, Schizachyrium scoparium, and Andropogon gerardii were grown under controlled hydroponic environmental conditions. Silicon leaf contents were positively correlated with solution
Si and ambient temperature but not with nutrient solution pH, electrical conductivity, or species. The Ge/Si ratio incorporated
into phytoliths shows a distribution coefficient (Ge/Si)phytolith/(Ge/Si)solution] of about 0.2 and is remarkably invariant between species, photosynthetic pathway, and solution temperature. Ge seems to
be discriminated against during the uptake and translocation of Si to the opal deposition sites by about a factor of five.
In the second experiment, a wider range of graminoid species (Agropyron smithii, Bouteloua gracilis, Buchloe dactyloides, Oryzopsis hymenoides, Schizachyrium scoparium and Andropogon gerardii) were grown in two different soil mediums. Plant phytoliths showed a distribution factor of about 0.4 for field grown grasses,
and 0.6 for potting soil grown grasses with no clear trends among the species. Evidence of the direction and degree of biological
Ge discrimination during plant uptake provides a geochemical finger print for plants and improves the utility of Ge/Si ratios
in studies of terrestrial weathering and links between Si cycles in terrestrial and marine systems. |
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Keywords: | Germanium Ge/Si Graminoid Phytolith Silicon |
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