Ecology of two geographically restricted Astragalus species (Fabaceae), A. bibullatus and A. tennesseensis, of the eastern United States |
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Authors: | Jerry M Baskin Carol C Baskin |
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Institution: | (1) Department of Biology, University of Kentucky, 40506-0225 Lexington, KY, U.S.A.;(2) Department of Plant and Soil Science, University of Kentucky, 40546 0321 Lexington, KY, U.S.A. |
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Abstract: | Astragalus bibullatus is endemic to limestone glades in the Central Basin of Tennessee, and except for one population in Illinois,A. tennesseensis is endemic to limestone glades in the Central Basin and in the Moulton Valley of Alabama. However,A. tennesseensis has been extirpated from four counties in Illinois, from its only known site in Indiana, from one county in Tennessee, and
from one county in Alabama.Astragalus bibullatus is closely related to the geographically wide-spread Great Plains taxonA. crassicarpus var.crassicarpus (sectionSarcocarpi), whereasA tennesseensis is the only taxon in sectionTennesseensis. Both species are shallow-rooted, hemicryptophyte perennials without vegetative reproduction, have no effective means of
seed dispersal, form long-lived seed banks, have similar life cycle phenologies, are intolerant of heavy shade, and have moderate
amounts of genetic diversity. Much. additional information is available on the autecology ofA. tennesseensis. Its primary habitat is the transition zone between open glades and glade woods, where physical environmental factors are
intermediate between those of the adjacent zones. Seedling-juvenile survival is low. Plants flower first in their second to
fifth year and only a few times before dying, are self-incompatible, respond to drought by shedding leaves and by accumulating
large amounts of proline, and compete poorly. Populations exhibit high fluctuations in number of individuals and have high
turnover rates. A greenhouse study ofA bibullatus andA crassicarpus var.crassicarpus did not identify any difference in responses of these species to light or soil moisture that could account for the great
differences in geographic ranges. Thus, historical factors were also considered to explain the narrow endemism ofA. bibullatus. Finally, we present previously unpublished data on the effect of light level and of competition with the cedar glade dominantSporobolus vaginiflorus in several watering regimes on growth ofA. tennesseensis. The role of these factors in restriction of this species to its transition zone microhabitat is discussed. |
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Keywords: | Astragalus bibullatus A tennesseensis autecology cedar glade endemics plant response to competition drought and shading |
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