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DIVERGENCE AND ADAPTATION IN ADJACENT PLANT POPULATIONS: STUDIES ON THE ECOLOGY AND PHYSIOLOGY OF THE BIG BLUESTEM (ANDROPOGON GERARDII VITMAN) - SAND BLUESTEM (ANDROPOGON HALLII HACK.) COMPLEX IN NEBRASKA (SANDHILLS, PRAIRIE, GENECOLOGY)
Examination of the morphology of 95 specimens of the big bluestem (Andropogon gerardii Vitmin)--sand bluestem (Andropogon hallii Hack.) complex indicates that along a local dune/meadow topographic gradient in the eastern Nebraska Sandhills, genetic variation is closely related to habitat variation and more specifically, to variation in soil moisture patterns, which in these sandy soils, is controlled by the depth to the underlying water table: sand bluestem genotypes occur on dry, upland sand dunes, big bluestem genotypes are restricted to nearby, naturally subirrigated, wet meadows, and hybrid genotypes are found in narrow dune/meadow transition zones where soil moisture levels are intermediate between dunes and meadows. In transplant experiments, both seedlings and adult rhizome transplants of sand bluestem survive longer on the dunes than big bluestem, which showed rapid and massive mortality following brief dry periods. Also, under similar drought conditions in common gardens, sand bluestem transplants maintained significantly higher leaf water potentials than either big bluestem or hybrid transplants. These and other transplant and physiological data indicate that there may be strong selection acting to keep drought sensitive big bluestem genotypes off the dunes and restricted to more mesic sites such as the Sandhills wet meadows. Factors excluding sand bluestem genotypes from adjacent meadows are less clear but may involve competitive abilities and/or an intolerance to flooded or saturated soils. Hybrid genotypes appear to lack the adaptive character combinations which allow them to inhabit parental habitats and are therefore confined to intermediate environments. Comparative studies on leaf anatomy revealed that leaf thickness, photosynthetic tissue, and mesophyll surface area (A('mes)/A) are greater in sand bluestem, but laboratory gas exchange measurements showed no inherent differences between bluestems in photosynthetic physiology, water use efficiency, or leaf chlorophyll and soluble protein contents suggesting that, in these C(,4) grasses, biochemical rather than physical (anatomical) factors are more important in controlling gas exchange processes. Water relations data from both field and laboratory studies showed little difference in stomatal physiology or osmoregulation capabilities; within the bluestems the evolutionary and adaptive response to moisture stress has apparently involved non-stomatal mechanisms, such as leaf rolling and/or epicuticular waxes, which act to control water loss under drought conditions.
BARNES, PAUL WARREN, "DIVERGENCE AND ADAPTATION IN ADJACENT PLANT POPULATIONS: STUDIES ON THE ECOLOGY AND PHYSIOLOGY OF THE BIG BLUESTEM (ANDROPOGON GERARDII VITMAN) - SAND BLUESTEM (ANDROPOGON HALLII HACK.) COMPLEX IN NEBRASKA (SANDHILLS, PRAIRIE, GENECOLOGY)" (1984). ETD collection for University of Nebraska - Lincoln. AAI8423759.