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Washington State University (2000)

Variation in Artemisia tridentata (Nutt) subspecies

Downs, Janelle Leora

Titre : Variation in Artemisia tridentata (Nutt) subspecies

Auteur : Downs, Janelle Leora

Université de soutenance : Washington State University

Grade : Doctor of Philosophy (PhD) 2000

Résumé
Subspecies of A. tridentata differentiate and segregate along major environmental gradients in precipitation, elevation, and available soil water. Five subspecies of A. tridentata are currently recognized : the three most common subspecies, tridentata, wyomingensis , and vaseyana , and two less common subspecies, spiciformis and xericensis . Three studies were completed to investigate genetic and physiological variation among subspecies of A. tridentata and to document the extent of variation in key characteristics among populations within ssp. wyomingensis . First, isozyme analysis of the genetic variability among populations of the five subspecies indicated that high percentages of polymorphic loci (67% to 89%), high average number of alleles per locus (A = 2.64), and high observed heterozygosity (0.238 to 0.503) compared to other widespread species. Genetic diversity values (Ht = 0.5531, Dst = 0.092, Gst = 0.167) indicate that 83.3% of genetic diversity is partitioned within populations of Artemisia tridentata . Of the 16.7% of the genetic diversity found among populations, only 1.7% is partitioned among subspecies. Second, comparison of leaf surface characteristics and leaf level gas exchange of subsp. wyomingensis and tridentata revealed larger cell size in the tetraploid ssp. wyomingensis (ssp. wyomingensis Beetle and Young) resulting in larger stomata compared to the diploid ssp. tridentata . Net photosynthesis (PSN) measured in spring and summer months was not significantly different between subspecies ; however, mean values measured for conductance (gwv ) in ssp. tridentata were consistently higher. Calculated values of intrinsic water use efficiency (IWUE, i.e., PSN/g) for ssp. wyomingensis were between 5% and 25% higher than ssp. tridentata during the first measurement year and 33% to 50% higher during the second measurement year. Third, evaluation of the gas-exchange response of subspecies and populations revealed that supplemental resources in the form of nutrients and water caused little measurable change in leaf-level gas exchange of subsp. tridentata . Supplemental resources decreased IWUE of subsp. wyomingensis compared to that measured under control conditions. Photosynthetic rates of three populations of subsp. wyomingensis from Hanford, Yakima, and Wenas Pass (low, intermediate, and high elevation) were not significantly different between populations under control conditions, but conductance and thus, water use efficiency varied between populations through the growing season.

Mots clés : Ecology, Gas exchange, Artemisia tridentata, Genetic diversity, Water conductance, Biological sciences Botany

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Page publiée le 17 février 2015, mise à jour le 29 octobre 2018