How do we find a true gypsophile?

The unique physical and chemical properties of gypsum soils have been used to explain species distribution across landscapes, however, past research on gypsophiles often has not encompassed broad analysis of soil-landscape-plant interaction and thus may have incorrectly labeled many species as gypsophiles. We use the example of the two reported gypsophiles, Arctomecon californica Torrey & Fremont and Eriogonum corymbosum Bentham var. nilesii Reveal found in the southern Mojave Desert, USA, to test the hypothesis that both species are gypsophiles and then draw conclusions from our work to evaluate past studies of gypsum soils, their landscapes and gypsophiles. Results from detailed pedologic analyses indicate that site characteristics affecting potential soil water content (topgraphic relief, soil particle size, depth to horizons perching water, and soil chemistry and mineralogy) differentiate habitat types and suggest surface differences affecting soil water content are more important for species success than sub-surface factors. Results suggest that gypsum is but one part of the explanation for A. californica and E corymbosum habitat differentiation and in fact neither species are gypsophiles. While few soils across all habitats had abundant gypsum, gypsum was of very low abundance at most sites and not limited to one habitat type. Foliar chemistry data also indicate neither species accumulates sulfur; the hypothesis that these species are gypsophiles is thus rejected. This research demostrates the complicated nature of determining the influence of soil and landscape on habitat differentiation and the necessity of detailed field-pedologic analysis when defining species limiting soil-landscape constraints. (C) 2009 Elsevier B.V. All rights reserved.