Weathering of biotite in the presence of arbuscular mycorrhizae in selected agricultural crops

The mutual association of roots and fungus, mycorrhizae, benefits the general ecosystem by producing soil clays from primary phyllosilicates. In laboratory experiments, X-ray diffraction analyses of clay materials showed that the fungus Glomus when inoculated onto barley and canola produced various types of less K-containing phyllosilicates (e.g., illites, smectites and hydroxy-interlayered vermiculites) from biotite and left some biotite (the K-rich mineral) intact. Non-inoculated plants left no intact biotite. Both non-inoculated and inoculated alfalfa produced only some illites from biotite. We propose that mycorrhizae inoculated samples exhibit selective K-extraction from some biotite particles to benefit plant growth and at the same time leaving unaltered biotite for future extractions. However, results from molecular DNA analysis (i.e., PCR) of fungal population, X-ray absorption near edge spectroscopic analysis of the oxidation of Fe2+ to Fe3+ and K-uptake by plants seems to indicate that the K-extraction process from biotite is by no means simple. The transformation of biotite and K (and Mg)-uptake depend on the plant fungus symbiotic system, and the formation of clay minerals will then be a function of plant type and symbiotic relations in the soils. (C) 2011 Elsevier B.V. All rights reserved.