Abstract
Deployment of well-adapted, water use efficient, and productive genotypes may be essential for the sustainability of both forests and wood supply for the forest industry, as climate change is increasing water stress around the world. This study aimed to characterize key traits among new genotypes of hybrid poplars (Populus spp.) in water use efficiency (WUE) and evaluate adaptive capacity to guide the selection of appropriate clones/hybrid types for commercial deployment in habitats with an increasing water deficit in northern, continental climates. Forty-five new hybrid poplar genotypes were compared at the age of 10, including two control clones, Walker and Okanese, growing in a common garden genetics trial in northern Alberta. We studied the relationships between their productivity and WUE, photosynthetic assimilation, transpiration, stomatal conductance, stomatal density and length, and leaf size and weight. In addition, the genetic variance and heritabilities of physiological and morphological characteristics related to WUE were calculated. Results of this study revealed that most of the clones showed an adaptive capacity to acclimatize (small and dense stomata) to the region of deployment. Morphological traits were characterized by higher heritabilities than physiological traits. Hybrids between Populus balsamifera and Populus maximowiczii species showed a slightly greater adaptive potential to the area of our study than the other tested cross types. Walker, a clone widely planted across the Canadian prairies, showed inferior WUE and productivity in comparison to the new genotypes tested. Selection and tree breeding for adaptation to climate change in the region of our investigation identified highly productive genotypes with dense, small stomata and a larger leaf area to dry mass ratio. As these traits are heritable, selection of clones with these traits will ensure a faster reaction of stomata when faced with a water deficit. The low genetic effect, heritability estimates, and high residual effect for physiological traits, impose a severe limitation on the use of gas exchange measurements under field conditions in tree improvement programs selecting for drought resistance.
Highlights
Climate change is increasing water stress in many areas of the world as a result of increasing temperatures and evapotranspiration, and more frequent episodes of climatic anomalies such as drought events [1]
Stomatal conductance was the most variable trait among physiological characteristics measured, while among morphological traits, leaf area (LA) and dry mass (DM) were characterized by the highest variability (CV ≈ 28%)
The variation among clones in physiological and morphological characteristics related to water use efficiency (WUE) at a leaf level suggests the possibility of achieving genetic gain through selection of these traits
Summary
Climate change is increasing water stress in many areas of the world as a result of increasing temperatures and evapotranspiration, and more frequent episodes of climatic anomalies such as drought events [1]. As trees (and other plants) take light energy as input to assimilate basic elements into biomass, hybrids can have more efficient growth than inbred plants because of the significant reduction in the energy-consuming processes of protein metabolism possibly due to the higher genetic diversity [10]. Such an effective mechanism in terms of water use consumption can be key for plants to thrive under more arid conditions in the face of climate change
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