Rapid Weathering of a Trioctahedral Mica by the Roots of Ryegrass

Abstract

Abstract The weathering of a trioctahedral mica (phlogopite, 2–100‐µm particle size) was investigated in the rhizosphere of ‘Turilo’ Italian ryegrass ( Lolium multiflorum Lam.). A special culture vessel made it possible to simulate a one‐dimensional macroscopic rhizosphere by developing a root mat on a polyamide net. This root mat was laid down on a mica‐agar substrate that was cut into slices 0.5 mm thick (parallel to the root mat) after 1, 2, 3, and 4 d of contact. The phlogopite mica was the sole source of both K and Mg for the plants. Whereas there was no significant release of Mg as a consequence of the roots' activity, K was released and concomitantly the mica lattice expanded after 3 d of continuous exposure to the root mat, in response to K uptake by plants. After 4 d, the vermiculitization of the phlogopite was detectable up to 1.5 mm from the root surface (i.e., the root mat) by x‐ray diffractometry. Such rapid mineralogical changes induced by roots support the view that primary minerals such as trioctahedral micas might contribute significantly to the supply of K to the plants, at least around the most active parts of the roots.