Experimental Determination of Silicon Isotope Fractionation in Rice.

Yan Sun,Xiao-Yan Li,Liang-Huan Wu

doi:10.1371/journal.pone.0168970

Abstract

Analyzing variations in silicon (Si) isotopes can help elucidate the biogeochemical Si cycle and Si accumulation processes of higher plants. 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. 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. 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. In addition, light Si isotopes (28Si) entered roots more readily than heavy Si isotopes (30Si) when the active mechanism was inhibited. Therefore, we conclude that biologically mediated isotope fractionation occurs during the uptake of Si by rice roots. 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.

Highlights

As the second most mass-abundant element on the Earth’s crust [1], the biogeochemistry of silicon (Si) has attracted steadily growing scientific interest
The biomass of rice plants grown in nutrient solutions with 1.70 and 8.50 mM Si was higher than that of plants grown in nutrient solutions with 0.17 mM Si, and the SiO2 content of the above- and belowground plant parts exhibited a similar trend (Fig 1)
When comparing the isotope compositions of rice plants to those of the nutrient solutions after plant uptake, the results suggest that heavy Si isotopes are preferentially absorbed by plants at lower levels of Si supplementation and that light Si isotopes are preferentially absorbed at higher levels of Si supplementation

Summary

Introduction

As the second most mass-abundant element on the Earth’s crust (after oxygen) [1], the biogeochemistry of silicon (Si) has attracted steadily growing scientific interest. The element is essential for diatom growth [1], and researchers have demonstrated that phytoplankton preferentially take up lighter Si isotopes from the ambient waters [2]. This biased uptake is expected to leave distinct isotopic fingerprints in both biogenic opal and the residual Sidepleted 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 [3,4,5]. Terrestrial plants require Si for optimal growth and are a major component of the global Si cycle [7]. Terrestrial plants can accumulate high levels of Si, ranging

Methods

Results

Conclusion