Family and sex-related responses of aspen (Populus tremuloides Michx.) seedlings to drought stress

Drought driven by increasingly warmer temperatures and longer growing seasons are shifting vegetation patterns. Trembling aspen ( Populus tremuloides Michx.), a dioecious tree species native to North America, has declined in health across much of its southern range, primarily due to drought. In dioecious tree species, females and males may incur different reproduction costs, potentially influencing growth and physiological responses to abiotic stress. In addition to sex, family origin (i.e., provenance) may also affect drought performance. We tested the growth and physiological responses of aspen seedlings under well-watered and sustained drought conditions to assess whether parent tree origin, family, or sex influenced seedling performance. Aspen seeds were extracted from female parent trees in two climatically different regions of Alberta (Boreal and Parkland) and grown in a commercial greenhouse. Sex was determined using the TOZ19 gene marker system, after which one-year-old overwinter dormant seedlings were grown for nine weeks under experimental conditions, in a split-plot replicated block design. Regions showed similar plasticity to drought. Families exhibited varied drought strategies, with both low- and high-productivity families identified. While sexes did not differ in growth or biomass production, females had higher intrinsic water-use efficiency ( i WUE) under well-watered conditions, whereas males had higher i WUE under drought. Overall, aspen seedlings demonstrated drought plasticity independent of origin and sex, exhibiting greater variation in performance under well watered conditions with a much more conserved response across families under drought stress.