A survey of soils formed on serpentinitic landscapes in California.

摘要

Serpentinite derived soils give rise to botanically distinct systems primarily as a result of inadequate Ca content of the parent material. I sampled 11 parent materials and soils across California at the soil survey modal location of the Henneke soil series (Clayey-skeletal, magnesic, thermic Lithic Argixerolls). I hypothesized that soils formed on serpentinitic landscapes have a range in extractable Ca, and total Ca and was correlated to vegetation Ca concentration. Total elemental analyses of the rocks underlying the soils showed CaO% varied from 0.01% to 23%, and CaO:MgO varied from 0.001 to 4. Rock at Napa and Tehama Counties, were xenolithic inclusions in the serpentinite landscape and contained no serpentine minerals (not serpentinites). The Napa County rocks contained almost no Ca-bearing minerals and probably would be identified as a serpentinite if relying upon elemental analysis and CaO:MgO alone.; Extractable soil Ca:Mg varied from 0.1 to 1.5, and total elemental Ca:Mg varied from 0.01 to 1.9. Soil extractable Ca was influenced by parent material mineralogy, where soils with a Ca:Mg of 0.2 or less were derived from serpentinite parent materials with only trace Ca-bearing minerals; soils with a Ca:Mg > 1 were derived from non-serpentinite parent materials, and soils with a Ca:Mg > 0.2 but 1 were derived from serpentinite parent material that had minor amounts of accessory Ca-bearing minerals. In a greenhouse study, the grass Vulpia microstachys concentration of above ground biomass Ca correlated better with soil extractable Ca (R2 = 0.89; P = 0.01) than with total elemental analysis Ca (R2 = 0.64; P 0.01). Extractable Ca was the best determinant of plant performance.; Zr, Ti, Y, or Nb were tested for use as an immobile element for mass balance strain calculation. Any would be acceptable for the Tehama County soil (non-serpentinitic rodingite), but Zr was not immobile in the Colusa County (serpentinitic) soil suggesting that the relative mobility of elements must be evaluated for each pedon on serpentinitic landscapes in order to identify suitable conservative elements for strain analysis.; Three profiles were compared and had quite different mass flux (1 to 11 g cm-2) of the major soil elements (Si, Al, Fe, Mg and Ca) illustrating that soil formation on serpentinitic landscapes can have quite different elemental fluxes.