Soil Type Tolerance In Rock Outcrop Plants: Species Of Non-Calcareous Substrates

摘要

Plants growing on rock outcrops are subject to environmental and edaphic extremes compared to nearby forested communities growing in deeper soil. Endemic and other characteristic outcrop species have adapted well to the shallow soil habitat of outcrops, but still might be absent from outcrops physically similar to those on which they occur. Presence can be influenced by the ability of species to tolerate various bedrock chemistries and to compete with other characteristic outcrop plants. To examine the role of soil type tolerance in determining the potential distribution of certain plants, we grew individuals of several species (Sedum nuttallianum, Hypericum gentianoides, and Oenothera linifolia) on a limestone substrate that they do not inhabit naturally, even when limestone outcrops are in close proximity to the variety of other rock outcrops where they do occur. Both H. gentianoides and O. linifolia were strongly intolerant of the limestone soil, indicating that edaphic factors are the dominant force limiting distribution. Growth also was reduced for S. nuttallianum, although the same physiological intolerance symptoms were not present as in the other species. Potentially, competitive interactions with Sedum pulchellum, a similar but larger stonecrop, are more important in limiting S. nuttallianum presence on limestone outcrops than is physiological intolerance to the calcareous substrate.