Genetic variability and drought responses of young and mature aspen in Alberta
Creators: Dias de Andrade Silva, Raiany
Publisher: name: University of Alberta Library
Year: 2024

<p>Trembling aspen (Populus tremuloides Michx.) is a dioecious clonal tree species with broad distribution in North America. In dioecious species, sexes are predicted to perform differently, based on the principle of allocation and the energy costs associated with reproduction. Aspen reproduce sexually through seeds and asexually through root suckers, forming clonal stands. The diversity of aspen clones was described in the past based on phenotypic assessments. Today, genetic markers have opened up a novel opportunity to explore the genetic diversity of aspen stands and the response of seedlings based on sex. The first breeding strategy for native aspen in Alberta was developed in 1995 with three regions selected based on aspen ecology, genetics, phenotype, and geography. It is imperative to understand the factors affecting clone presence, genetic diversity, and sex distribution in aspen stands, to inform aspen improvement programs in Alberta and to provide insights into the ecological responses of aspen to abiotic stress. This thesis explored sex differential performance in aspen on seedlings (Chapter 2) and mature stands (Chapter 3), including aspects of climate, and the genetic diversity of aspen stands within the AW2 aspen tree improvement region, using microsatellite markers and phenotype (Chapter 4). <br>
Chapter 2 tested the response of aspen seedlings under drought and well-watered conditions to assess if parent tree origin has an influence on seedling performance and if different genotypes and sexes present differential drought performances. Seeds were extracted from 19 female parent trees, from two climactically different regions in Alberta. Sex was determined using the TOZ19 gene sequence. Seedlings were maintained in a greenhouse under well-watered and sustained drought conditions in a split-plot replicated block design experiment. Parkland seedlings showed adaptation to drought conditions. Genotypes showed varied drought strategies, with low and high-productivity families identified. While sexes did not differ in growth or biomass production, female seedlings had higher intrinsic water-use efficiency (iWUE) under well-watered conditions, and males had higher iWUE under drought. <br>
Chapter 3 described the distribution of mature male and female aspen trees within the southern portion of the AW2 region and examined climate as a potential factor driving the distribution of sex. A minimum of 19 and maximum of 30 trees were sampled in 12 mature aspen stands, in four different areas. Data collected include DNA samples; diameter at breast height; wood density, ring growth, and stand age. Climate data were obtained for each study site using the BioSIM software. An approximate 2:1 female:male sex ratio was observed, and males and females showed similar overall diameter growth and wood density. For the timeframe explored, this study did not find different sex responses to drought in mature aspen trees.<br>
In Chapter 4, aspen clonal structure and ploidy were described in the AW2 (Pembina) region. The same trees from Chapter 3 were studied in addition to DNA collected from trees along transects connecting the stands. Phenotypic assessments were used to delineate putative clones and microsatellite markers were used to confirm clonal identity, diversity, and ploidy. Natural populations within the AW2 region showed high levels of genetic diversity including evidence of occurrence and accumulation of somatic mutations. Mutations introduce more complexity and variability to those populations. Polyploids (i.e., 3n or 4n) had better growth and performance during and post-drought.<br>
This study showed that aspen seedlings show plasticity to drought independent of origin and sex and that genetic variability plays a main role in the maintenance of higher-performing genotypes. In mature aspen stands costs of reproduction may be manifested beyond the production of seeds, with differential allocation of energy in females and males also occurring in root and stem growth. Finally, natural aspen stands exhibited greater diversity and complexity than found previously. The use of trees of different ploidies, sexes, and genotypes in improvement programs and aspens stands would allow for increased growth under varied environmental conditions.</p>