Response to carbon monoxide by geographic variants in Acacia farnesiana.
A B S T R A C T Differences in degree of defoliation in CO-air mixtures were shown by geographic variants in Acacia farnesiana (L.) Willd., a widespread, weedy, pantropic, leguminous tree. Laboratorygerminated seedlings from MazatlAn (MAME-1), Sinaloa, Mexico, showed greater sensitivity to a CO gradient than plants from Point Tuna (PORO), Puerto Rico. Seedlings of both strains grown under a light intensity of 200 ft-c showed greater sensitivity to CO than those grown under 1,800 ft-c. When intact plants of 17 geographic variants grown at low-light intensities were exposed to 2%Fo CO in air, 11 strains (Mexico,8; Texas, 1; California, 1; Guatemala, 1) showed almost complete defoliation. The other six strains-from Brazil, Hawaii, Puerto Rico, 1Ttaly, Algeria, and Michoac4n, Mexico-showed defoliation averaging from 23 to 70%. The significance of the CO-defoliation response is difficult to explain in terms of the natural distribution of A. farnesiana. It is suggested that this response may be correlated with some biochemical process of adaptive significance. GEOGRAPHIC variants in Acacia farnesiana (L.) Willd. being studied at the Plant Ecology Research Laboratory differ in several parameters, but the most bizarre difference is one shown by exposure to low concentrations of carbon monoxide. While certain strains show nearly total leaf loss after 24-hr exposure to CO, other strains show little or no defoliation. First observed as a result of accidental exposure to CO, the geo
Stem Orientation in Two Populations of Acacia farnesiana from Mexico Under Controlled Environmental Conditions
The orientation of stem growth in upright plants from an inland population at Saltillo, Coahuila, and in prostrate plants from a beach population at Mazatlan, Sinaloa, was examined under several conditions of photoperiod, temperature, and light intensity. Prostrateness is enhanced by lower temperatures, shorter photoperiods, and higher light intensities in both populations but is induced to a greater degree and over a wider range of conditions in the naturally prostrate form. Under longer day lengths, 16 hr, and higher temperatures, 32-24 C, the prostrate form develops almost upright and is not significantly more prostrate than the naturally upright form. Regenerated stems produced under high light intensities were significantly more prostrate in the beach population than were stems of the inland population, but under low light intensities both populations produced upright stems. The results suggest that niche plasticity of the prostrate population offers selective advantage in a subtropical beach ecosystem.
ECOTYPIC DIFFERENTIATION WITHIN FOUR NORTH AMERICAN PRAIRIE GRASSES. II. BEHAVIORAL VARIATION WITHIN TRANSPLANTED COMMUNITY FRACTIONS
Ecological variation within transplanted community fractions, containing Andropogon scoparius Michx., A. gerardi Vitman, Panicum virgatum L. and Sorghastrum nutans (L.) Nash, included broad behavioral and morphological differentiation. In Austin, Texas, during 1958-1962, southern community fractions that contained early spring activity, late flowering and late fall dormancy included taller plants than early-flowering, northern community fractions. The tallest populations in all 4 species originated in Texas. In P. virgalum, size of leaves and panicles showed north-south trends similar to culm height values. Leaf pubescence and leaf glaucousness in all 4 species showed geographic patterning that was not correlated with north-south maturity gradients. Greatest pubescence was on clones in community fractions from pine woods in the Southeast. Glaucousness was concentrated in community fractions from central Texas northward to Nebraska. ECOLOGICAL variation in 4 widely distributed prairie grasses includes a broad range of ecotypic differentiation and morphological variation. The present investigation of ecological variation is the first involving a series of transplanted community fractions and has been a comparison of morphological patterning. The second study (McMillan, 1965b) compares the behavioral range of the transplanted populations. For the comparison of community fractions from the eastern United States with those of the central grassland region, population samples of latitudinally diverse origin were assembled in Austin, Texas. From 1958 to 1962, the maturity range of eastern clones showed north-south correlations similar to those of the central grassland. Earliest spring activity, latest flowering, and latest dormancy were in southern populations. Northern community fractions from Massachusetts to North Dakota showed early flowering and a short span separating initial anthesis among the species-populations. The length of the growing period and other temperature-related phenomena in the native habitats appeared critical in the selection of the behavioral variation. The broad morphological patterning was investigated to determine its relation to differentiation that had included a range of leaf pubescence and glaucousness in the 4 taxa in Texas (Bragg and lVMcMillan, 1962). Although the community fractions exhibiting the morphological extremes of pubescence and glaucousness were not the extremes in maturity differentiation in Texas,