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Intraspecific Variability in the Response of Certain Native Plant Species to Serpentine Soil

Arthur R. Kruckeberg
American Journal of Botany
Vol. 38, No. 6 (Jun., 1951), pp. 408-419
Stable URL: http://www.jstor.org/stable/2438248
Page Count: 12
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Abstract

In California, soils derived from serpentine rock support a unique flora, many species of which are narrowly endemic on this infertile soil type. Previous soil analyses of serpentine have shown that this soil is unusually high in magnesium, chromium, and nickel. Soils derived from this ultra-basic rock are also markedly deficient in calcium, nitrogen, phosphate, and occasionally molybdenum. Although chiefly restricted to serpentine, strains of Streptanthus glandulosus are occasionally also found on non-serpentine soils. When grown in experimental cultures, collections of strains from non-serpentine localities showed a marked intolerance to serpentine soil, whereas collections of other strains of the same species from serpentine sites attained normal growth on serpentine soil. The distribution pattern and intraspecific differences in serpentine tolerance of S. glandulosus have suggested "biotype depletion" as one possible mode of origin of serpentine endemics. This species is interpreted as being on the verge of becoming a strict serpentine endemic once its few non-serpentine biotypes have been eliminated. Tests for tolerance to serpentine soil were conducted on species of other genera occurring naturally on serpentine as well as on non-serpentine soils ("bodenvag" species). As was shown for Streptanthus, two of these non-endemic species - Gilia capitata and Achillea borealis-could be separated into serpentine-intolerant and serpentine-tolerant races on the basis of their growth responses on serpentile soil. From a biosystematic standpoint these soil races can be thought of as edaphic ecotypes. Yet these particular physiological differences are often wholly superimposed upon a single climatic ecotype.

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