Variation in carbon isotope discrimination in relation to plant performance in a natural population of <Emphasis Type="Italic">Cryptantha flava</Emphasis> |
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Authors: | B?B?Casper Email author" target="_blank">I?N?ForsethEmail author D?A?Wait |
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Institution: | (1) Department of Biology, University of Pennsylvania, Philadelphia, PA 19104-6018, USA;(2) Department of Biology, University of Maryland, College Park, MD 20742 , USA;(3) Department of Biology, Southwest Missouri State University, Springfield, MO 65804, USA |
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Abstract: | Few studies of phenotypic selection have focused on physiological traits, especially in natural populations. The adaptive
significance of plant water-use efficiency, the ratio of photosynthesis to water loss through transpiration, has rarely been
examined. In this study, carbon isotopic discrimination, Δ, an integrated measure of water-use efficiency, was repeatedly
measured in juveniles and adults in a natural population of the herbaceous desert perennial Cryptantha flava over a 4-year period and examined for plasticity in Δ, consistency between years in values of Δ, and evidence for selection
on Δ phenotypes. There was significant concordance in Δ values among the 4 years for adult plants and significant correlations
in Δ values measured in different years for juveniles and adults combined. The wettest year of the study, 1998, proved an
exception because Δ values that year were not correlated with Δ values in any other year of the study. Consistency in Δ measured
on the same plants in different years could indicate genotypic variation and/or consistency in the water status of the microhabitats
the plants occupied. Two forms of plasticity in Δ were also evident; mean seasonal values were correlated with precipitation
the preceding autumn, and Δ values also declined with plant size, indicating increasing water-use efficiency. Phenotypic selection
was evident because in the first year of the study juvenile plants that would survive until year five averaged lower Δ values
than did those that failed to survive. During the driest year, 2000, Δ was significantly negatively correlated with adult
plant size, measured as the number of leaf rosettes, but the negative relationship between Δ and the number of flowering stalks,
a more direct measure of fitness, was not significant. These results suggest that the direction of phenotypic selection on
Δ changes as plants grow. |
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Keywords: | Cryptantha flava Integrated water-use efficiency Phenotypic plasticity Phenotypic selection Selection on WUE |
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