Productivity, Growth Patterns, and Cellulosic Pulp Properties of Hybrid Aspen Clones

Morphological and Physiological Responses of Hybrid Aspen (Populus tremuloides Michx. × Populus tremula L.) Clones to Light In Vitro

Micropropagation of fast-growing tree genotypes such as the hybrid aspen (Populus tremuloides Michx. × Populus tremula L.) is increasing. The efficiency of micropropagation depends on the luminaires, hence luminescent electric diodes (LED), which emit light of a narrow spectrum, are gaining popularity. Mostly, different LEDs are combined to increase the photosynthetic efficiency. However, light also acts as an environmental signal, which triggers specific responses in plants, which are genotype specific, and regarding hybrid aspen, are likely affected by heterosis. In this study, morphological and physiological responses of clones of hybrid aspen with contrasting field performance to the spectral composition of illumination were studied in vitro. Among the 15 variables measured, area of leaves and concentration and ratio of chlorophyll a and b explained most of the variance (58.6%), thereby linking a specific combination of traits to productivity. These traits and their responses to light were affected by heterosis, as indicated by the clone-treatment interaction, particularly for the clone's moderate productivity. The top-performing clones were little sensitive to illumination due to efficient photosystems. Nevertheless, illumination with wider spectral composition had generally positive effects on plantlet performance. Accordingly, clone-specific illumination protocols and luminaries capable of it are advantageous for the efficiency of micropropagation of hybrid aspen.

Differences in Environmental and Hormonal Regulation of Growth Responses in Two Highly Productive Hybrid Populus Genotypes

Phenotypic plasticity, in response to adverse conditions, determines plant productivity and survival. The aim of this study was to test if two highly productive Populus genotypes, characterised by different in vitro etiolation patterns, differ also in their responses to hormones gibberellin (GA) and abscisic acid (ABA), and to a GA biosynthesis inhibitor paclobutrazol (PBZ). The experiments on shoot cultures of ‘Hybrida 275′ (abbr. H275; Populus maximowiczii × P. trichocarpa) and IBL 91/78 (Populus tremula × P. alba) were conducted by either modulating the physical in vitro environment or by adding specific chemicals to the nutrient medium. Our results revealed two main sets of differences between the studied genotypes in environmental and hormonal regulation of growth responses. First, the genotype H275 responded to darkness with PBZ-inhibitable shoot elongation; in contrast, the elongation of IBL 91/78 shoots was not affected either by darkness or PBZ treatment. Secondly, the explants of H275 were unable to recover their growth if it was inhibited with ABA; in contrast, those of IBL 91/78 recovered so well after the temporal inhibition by ABA that, when rooted subsequently, they developed longer shoots and roots than without a previous ABA treatment. Our results indicate that GA catabolism and repressive signalling provide an important pathway to control growth and physiological adaptation in response to immediate or impending adverse conditions. These observations can help breeders define robust criteria for identifying genotypes with high resistance and productivity and highlight where genotypes exhibit susceptibility to stress.

Extraction of Cellulose Polymeric Material from Populus tremula Fibers: Characterization and Application to the Adsorption of Methylene Blue and Crystal Violet

Cellulose is the most widely available biopolymer which is extensively used for several applications including textiles, composites, pharmaceutical, water treatment, etc. In this investigation, cellulose was chemically extracted from Populus tremula seed fibers. Samples were characterized using FT-IR, SEM, XRD, and TGA-DTA analyses. FT-IR spectrum of the extracted cellulose confirmed that hemicellulose and lignin were removed during alkali and bleaching treatments. SEM images showed the partially roughened surface of the fiber due to the removal of non-cellulosic elements and surface impurities during chemical modification. The crystallinity index values for untreated Populus tremula fibers and extracted cellulose were calculated to be 32.8% and 58.9%, respectively. The obvious increase in the crystallinity index for the extracted cellulose confirmed the removal of amorphous compounds present in raw populus. Alkali-treated populus fibers were more thermally stable than raw fibers. All changes observed after alkali and bleaching treatments evidenced the removal of amorphous contents and non-cellulosic components in raw populus fibers. Extracted cellulose exhibited excellent adsorption capacities of methylene blue (140.4 mg g⁻¹) and crystal violet (154 mg g⁻¹). The pseudo second order equation fitted well the kinetic data indicating a chemi-sorption process. The Freundlich model complied well with the experimental data suggesting that the adsorption of the studied dyes was multilayer.

Wood and Pulping Properties Variation of Acacia crassicarpa A.Cunn. ex Benth. and Sampling Strategies for Accurate Phenotyping

Research Highlights: This study provides a comprehensive set of wood and pulping properties of Acacia crassicarpa A.Cunn. ex Benth. to assess variation and efficient sampling strategies for whole-tree level phenotyping. Background and Objectives: A. crassicarpa is an important tree species in Southeast Asia, with limited knowledge about its wood properties. The objective of this study was to characterize important wood properties and pulping performance of improved germplasm of the species. Furthermore, we investigated within-tree patterns of variation and evaluated the efficiency of phenotyping strategies. Materials and Methods: Second-generation progeny trials were studied, where forty 50-month-old trees were selected for destructive sampling and assessed for wood density, kraft pulp yield, α-cellulose, carbohydrate composition, and lignin content and composition (S/G ratio). We estimated the phenotypic correlations among traits determined within-tree longitudinal variation and its importance for whole-tree level phenotyping. Results: The mean whole-tree disc basic density was 481 kg/m3, and the screened kraft pulp yield was 53.8%. The reliabilities of each sampling position to predict whole-tree properties varied with different traits. For basic density, pulp yield, and glucose content, the ground-level sampling could reliably predict the whole-tree property. With near infrared reflectance spectroscopy predictions as an indirect measurement method for disc basic density, we verified reduced reliability values for breast height sampling but sufficiently correlated to allow accurate ranking and efficient selection of genotypes in a breeding program context. Conclusions: We demonstrated the quality of A. crassicarpa as a wood source for the pulping industry. The wood and pulping traits have high levels of phenotypic variation, and standing tree sampling strategies can be performed for both ranking and high-accuracy phenotyping purposes.

Genetic parameters of growth and adaptive traits in aspen (Populus tremuloides): Implications for tree breeding in a warming world

Aspen (Populus tremuloides Michx) is a widespread commercial forest tree of high economic importance in western Canada and has been subject to tree improvement efforts over the past two decades. Such improvement programs rely on accurate estimates of the genetic gain in growth traits and correlated response in adaptive traits that are important for forest health. Here, we estimated genetic parameters in 10 progeny trials containing >30,000 trees with pedigree structures based on a partial factorial mating design that includes 60 half-sibs, 100 full-sib families and 1,400 clonally replicated genotypes. Estimated narrow-sense and broad-sense heritabilities were low for height and diameter (~0.2), but moderate for the dates of budbreak and leaf senescence (~0.4). Furthermore, estimated genetic correlations between growth and phenology were moderate to strong with tall trees being associated with early budbreak (r = -0.3) and late leaf senescence (r = -0.7). Survival was not compromised, but was positively associated with early budbreak or late leaf senescence, indicating that utilizing the growing season was more important for survival and growth than avoiding early fall or late spring frosts. These result suggests that populations are adapted to colder climate conditions and lag behind environmental conditions to which they are optimally adapted due to substantial climate warming observed over the last several decades for the study area.

Selection of Poplar Genotypes for Adapting to Climate Change

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.