Uptake and transport of montmorillonite particles by wheat

Abstract

Elucidation of the interactions of crop plants with clay minerals is essential for understanding the roles of clay minerals in terrestrial ecosystems. The prevailing hypothesis suggests that the physiological barriers of plant roots prevent the direct uptake of these large-size particles. However, whether crops can directly take up clay mineral particles remains unknown. Montmorillonite is a ubiquitous and important clay mineral in soil. This study used covalent fluorescence labeling and microscopic techniques to investigate the uptake and transport of montmorillonite particles by wheat (Triticum aestivum L.) in hydroponic solution, quartz sand matrix, and sandy loam soil. Additionally, the surface attachments of montmorillonite particles in xylem sap were analyzed at the nanoscale level with transmission electron microscopy and atomic force microscopy combined with infrared spectroscopy. Our results confirmed that micrometer-sized montmorillonite particles could enter the root steles of wheat seedlings from the sites of new lateral root emergence and were subsequently transported upward to the shoots and leaves through the vasculature via the transpiration stream. In this process, the surfaces of the montmorillonites adsorbed inorganic mineral nutrients and were covered by a layer of biomolecular coronas. This study reveals the potential for crop plant uptake of micrometer-sized montmorillonite particles and complements existing theories regarding the interactions of clay minerals with crop plants. Furthermore, the findings may lay a foundation for future studies on clay mineral interactions with crop plants in terrestrial ecosystems.