Terrestrial plants require Si for optimal growth and are also a major component of the global Si cycle. However, Si is also ‘quasi-essential’ for the growth of higher plants, and as a result, researchers have also begun to investigate Si isotope-related processes in terrestrial plants. This biased uptake is expected to leave distinct isotopic fingerprints in both biogenic opal and the residual Si-depleted waters, and an increasing number of studies have attempted to use Si stable isotope abundances from marine biogenic materials (e.g., diatoms) and seawater to elucidate marine distribution and cycling of Si. The element is essential for diatom growth, and researchers have demonstrated that phytoplankton preferentially take up lighter Si isotopes from the ambient waters. In addition, both active and passive Si uptake components co-exist in rice, and the fractionation effect is enhanced when more Si is absorbed by plants.Īs the second most mass-abundant element on the Earth’s crust (after oxygen), the biogeochemistry of silicon (Si) has attracted steadily growing scientific interest. Therefore, we conclude that biologically mediated isotope fractionation occurs during the uptake of Si by rice roots. In addition, light Si isotopes ( 28Si) entered roots more readily than heavy Si isotopes ( 30Si) when the active mechanism was inhibited. We found that an active mechanism was responsible for the majority of Si uptake and transport at lower Si levels and that the uptake of Si by rice roots was significantly suppressed by both low temperature and metabolic inhibitors.
SI ELEMENT ACTIVE ISOTOPES ACTIVE SERIES
In the present study, we investigated the isotope fractionation that occurs during the uptake and transport of Si in rice, using a series of hydroponic experiments with different external concentrations of Si. Importantly, the composition of Si isotopes in higher plants has yet to be studied comprehensively and our knowledge of the distribution of Si isotopes in higher plants lags behind that of Si isotopes in marine organisms, such as diatoms. Analyzing variations in silicon (Si) isotopes can help elucidate the biogeochemical Si cycle and Si accumulation processes of higher plants.
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