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Life History Variation of Common Mullein (Verbascum Thapsus): II. Plant Size, Biomass Partitioning and Morphology

James A. Reinartz
Journal of Ecology
Vol. 72, No. 3 (Nov., 1984), pp. 913-925
DOI: 10.2307/2259540
Stable URL: http://www.jstor.org/stable/2259540
Page Count: 13
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Life History Variation of Common Mullein (Verbascum Thapsus): II. Plant Size, Biomass Partitioning and Morphology
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Abstract

(1) For a description of the range of variation in plant size and biomass partitioning of Verbascum thapsus, plants were sampled randomly from twelve populations from southern Canada to southern Texas. Correlations between morphological traits, life history and population dynamics were investigated. Genetic components of latitudinal variation in biomass partitioning were separated from environmental effects by growing plants from seed in a common garden. (2) Many environmentally induced and genetic differences were found among the populations. There was a strong positive correlation between plant size and proportion of biomass devoted to reproduction. Large plants also had a smaller root to shoot quotient than small plants. The positive relationship between plant size and reproductive effort was caused by indeterminate reproductive growth after leaf, caudex and root growth had ceased. (3) North Carolina genotypes were lighter than plants from Canada or Texas. However, they devoted a greater proportion of their dry weight to stalks and hence were taller. North Carolina plants also produced smaller seeds than the ecotypes from the edges of the range of the species. (4) Roots comprised a larger fraction of plant biomass in the Texas ecotypes than in the northern plants. In the field, Canadian populations had the largest caudices, relative to total plant size. (5) Texas ecotypes had larger capsules than those from farther north. (6) Compared with other monocarpic species, V. thapsus had an extremely low reproductive effort (11-23% of biomass) and seed output (4-8%). Reproductive efforts and seed outputs of other monocarpic species average 40% and 25%, respectively.

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