Rapid Weathering of a Trioctahedral Mica by the Roots of Ryegrass

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.

Properties of soils influenced by ectomycorrhizal fungi in hybrid spruce [Picea glauca × engelmannii (Moench.) Voss]

“…The trends in the amounts of mica, chlorite, kaolinite, and 2:1 expandable clays in ECS compared to N-ECM soils support earlier findings (e.g., Hinsinger et al 1992;Kodama et al 1994;Arocena et al 1999). Kaolinite seems to weather faster than mica and chlorite in ECS compared to N-ECM soils.…”

“…In addition, Robert and Berthelin (1986) showed micrographs of hyphae probing between mica flakes to extract essential K + . In many studies, rootinduced release of interlayer K + was the main reason for the high rates of chemical weathering in rhizosphere zones (Hinsinger et al 1991;Hinsinger et al 1992;Hinsinger and Jaillard 1993;Kodama et al 1994). The formation of vermiculite (a weathering product of mica) is usually caused by the release of K + from mica (Fanning et al 1989) and can take place within a few days (Hinsinger et al 1992).…”

“…In many studies, rootinduced release of interlayer K + was the main reason for the high rates of chemical weathering in rhizosphere zones (Hinsinger et al 1991;Hinsinger et al 1992;Hinsinger and Jaillard 1993;Kodama et al 1994). The formation of vermiculite (a weathering product of mica) is usually caused by the release of K + from mica (Fanning et al 1989) and can take place within a few days (Hinsinger et al 1992). Primarily, whenever the uptake of K + by plant roots was greater than the release of K + from the mica, the release of K + from mica was enhanced (Arocena et al 1999).…”

Mineralogy of Rhizospheric and Non-Rhizospheric Soils in Corn Fields

“…Although the vermiculitization of mica by plant growth has been reported since the investigation of Mortland et al (1956), it took a long time to have the direct evidence that the vermiculitization of trioctahedral micas can take place within several weeks in the rhizosphere (Hinsinger 1993;Hinsinger et al 1992Leyval et al 1990). Those latter reports were based on pot experiments.…”

“…For example, vermiculitization of biotite by plant growth is known (Mortland et al 1956). and Hinsinger et al (1992) demonstrated that such a vermiculitization could occur within a matter of several weeks (even a few days in some cases) in the rhizosphere. Recently, Keller (1990a, 1990b) showed that the mineralogy of the rhizosphere differed from that of the bulk soil in forest soils.…”