Distinct silicon and germanium pathways in the soil-plant system: Evidence from banana and horsetail
(2009) Journal of Geophysical Research — Vol. 114, p. G02013 (2009)
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- Plants strongly impact the continental silicon cycle by taking up Si and precipitating opal phytoliths which are recycled into the soil. Studying Ge incorporation, a chemical analog of Si, relative to Si may provide a useful tracer of Si pathways. However, Ge uptake and transport through plants and the impact on Ge/Si of phytoliths remain poorly understood. Here, we report Ge uptake and accumulation and Ge/Si fractionation in all plant parts and solutions from: (1) hydroponic banana, (2) in situ sampled banana, and (3) horsetails. We further combine these data with delta Si-29 from banana plants. Our data reconcile opposite conclusions drawn from previous studies on Ge uptake and pathways. No discrimination of Ge occurred at the root-solution interface. Banana and horsetails were shown to accumulate Ge in roots: a previous study provided evidence of low Ge/Si ratios in root phytoliths which contrasts with high bulk Ge/Si ratios in roots we report here. This suggests that Ge is organically trapped in roots. Consequently, shoots display lower Ge/Si ratios, without fractionation between shoot parts since Ge would follow transpiration stream as silicon, and is not discriminated between shoot parts. This contrasts with the two-step discrimination against heavy Si isotopes, at the root-solution interface, and then within the shoots. The soil composition (clays versus Fe oxides) has a leading role on the Ge/Si signatures of plants which may in turn impact on the Si and Ge fluxes to the global ocean.
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Delvigne, C., Opfergelt, S., Cardinal, D., Delvaux, B., & André, L. (2009). Distinct silicon and germanium pathways in the soil-plant system: Evidence from banana and horsetail. Journal of Geophysical Research, 114, G02013. https://doi.org/10.1029/2008JG000899 (Original work published 2009)