Three trioctahedral micas and one dioctahedral mica (1–5µ size fractions) were used as sources of K+ for seven fungi grown in nutrient solution buffered at pH 6. Vermiculite formed from the mica. The mechanism involved was exchange of solution Na+ for mica K+, with the fungi functioning as K+‐sinks. Reducing the concentration of solution Na+ from 0.054M to 0.017M resulted in decreased rate of utilization of mica K+. Growth of fungi and release of K+ were greater for trioctahedral micas than for the dioctahedral mica and generally followed the K+ ease‐of‐release pattern established using sodium tetraphenylboron and NaCl solutions. The fungi differed in their capacities to promote the mica‐to‐vermiculite transition, and this was probably due mainly to their relative effectiveness as K+‐sinks.
At two locations in the southern Appalachian Mountains, soils at two slope positions on north‐ and south‐facing landscapes were described, sampled, and analyzed to determine the relative effect of slope aspect and position upon the differentiation of the parent rock into soil profiles. At the southwestern Virginia study area, the parent rocks are highly siliceous sandstone and siltstone, whereas, the parent rock in southwestern North Carolina is a granitic biotite gneiss.Soils developed from the siliceous parent material were very similar in morphological, physical, chemical, and mineralogical properties irrespective of aspect and slope position. In contrast, there was a high degree of soil profile differentiation at the two slope positions and on the two aspects in North Carolina. In addition to differences in morphological and physical properties, there are distinct differences in the clay mineral suites on opposing aspects. Kaolin and the pedogenic 2:1–2:2 intergrade minerals are predominant in the soils of the north‐facing landscapes, whereas, gibbsite is the major clay mineral in the soils of the south‐facing landscape.
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