Xylem cells are surrounded by primary and secondary cell walls. Formation of primary walls is regulated by the cell wall integrity surveillance system, but it is unclear if the deposition of secondary walls is similarly regulated. To study this question, we introduced to aspen three different enzymes cleaving cell wall-localized xylan and we suppressed xylan synthase components either ubiquitously or specifically during secondary wall formation using the Populus trichocarpa GT43B promoter. When xylan was ubiquitously altered, 95% of lines showed reduced growth, whereas when it was altered during secondary wall deposition, 30% of lines grew better, with the rest having no growth impairment, suggesting opposite effects of primary and secondary wall disturbances. To detect the mechanism of growth stimulation by disturbed deposition of the secondary wall, we analyzed changes in wood quality traits, chemistry, transcriptomics, metabolomics and hormonomics in transgenic lines. We found increased tension wood production, reduced S- and H-lignin, and changes in several metabolites in common in these lines. Remorin REM1.3 and NRL2 (NPH3 family) transcripts increased, and changes in jasmonates, abscisic acid, and salicylic acid occurred in secondary wall-forming xylem, suggesting their involvement in secondary wall integrity surveyance and signaling. The data indicate that a unique program mediates responses to secondary wall impairment that induces growth

Background: The evaluation of genomic selection (GS) efficiency in forestry has primarily relied on cross-validation schemes that split the same population within a single generation for both training and validation. While useful, this approach may not be reliable for multigenerational breeding. To our knowledge, this is the first study to assess genomic prediction in Norway spruce using a large dataset spanning two generations in two environments. We trained pedigree-based (ABLUP) and marker-based (GBLUP) prediction models under three approaches: forward prediction, backward prediction, and across-environment prediction. The models were evaluated for ring-width, solid-wood and tracheid characteristics, using ~ 6,000 phenotyped and ~ 2,500 genotyped individual. Predictive ability (PA) and prediction accuracy (ACC) were estimated using an independent validation method, ensuring no individuals were shared between training and validation datasets. To assess the trade-off between comprehensive radial history and practical direct methods, we compared GBLUP models trained with cumulative area-weighted density (AWE-GBLUP) and single annual-ring density (SAD-GBLUP) from mother plus-trees. These models were validated using early and mature-stage progeny density measurements across two trials. Results: Despite the smaller number of individuals used in the GBLUP models, both PA and ACC were generally comparable to those of the ABLUP model, particularly for cross-environment predictions. Overall, forward and backward predictions were significantly higher for density-related and tracheid properties, suggesting that across-generation predictions are feasible for wood properties but may be challenging for growth and low-heritability traits. Notably, SAD-GBLUP provided comparable prediction accuracies to AWE-GBLUP, supporting the use of more practical and cost-effective phenotyping methods in operational breeding programs. Conclusions: Our findings highlight the need for context-specific models to improve the accuracy and reliability of genomic prediction in forest tree breeding. Future efforts might aim to expand training populations, incorporate non-additive genetic effects, and validate model performance across cambial ages while accounting for climatic variability during the corresponding growth years. Overall, this study offers a valuable foundation for implementing GS in Norway spruce breeding programs.

Wood is the most abundant renewable natural resource composed of different polysaccharides and lignin, but its utilisation is hampered by intermolecular linkages between these components forming lignin-carbohydrate complexes (LCCs) causing recalcitrance. The links between glucuronoxylan and the γ-C of lignin (γ-ester linkages) are thought to contribute to one-third of LCCs, but direct evidence for their natural occurrence and their role in recalcitrance has been scarce so far. To address these issues, Phanerochaete carnosa glucuronoyl esterase (PcGCE), hydrolysing γ-ester linkages, was expressed in cell walls of developing wood in hybrid aspen (Populus tremula L. × tremuloides Michx.). The enzyme reduced HSQC 2D NMR signals corresponding to the γ-esters and xylan in dioxane-extracted LCCs without altering glucuronoxylan content or structure. This increased acid solubility of lignin and lignin content. Reduced wood recalcitrance was shown by increased sugar yields and glucose production rates (by approx. 20%) in saccharification without pretreatment and increased xylan extractability by subcritical water (by approx. 70%). Moreover, trees expressing PcGCE exhibited greater primary and secondary growth. Transcriptomics and metabolomics analyses in developing wood suggested that growth could have been induced by a higher transcription of SMR2 and RPOTmp, which was likely triggered by the secondary cell wall integrity signalling. The results provide evidence for the natural existence of LCC γ-esters and their significant contribution to lignocellulose recalcitrance. Furthermore, they show that reducing γ-ester linkages could increase plant productivity.

Spatial information on wood structure and chemistry is crucial for understanding wood functionality. We present a high-throughput and high-resolution near-infrared (NIR) method for combined imaging of the physical and chemical properties of stem sections from Populus trees. Pyrolysis-GC/MS data was used for sensitive and spatially resolved calibration of wood chemistry while SilviScan™ analyses provided reference data for wood physical properties with 25 μm resolution for wood density and 0.2-2.0 mm for microfibril angle (MFA). NIR prediction models were trained and calibrated on material from both field- and greenhouse-grown trees. Thus, the method was developed for NIR imaging of stem samples as small as 4 mm in diameter with an image resolution of 0.03 mm for small-diameter samples and 0.5 mm for samples with multiple annual rings. The NIR model performance, tested against data not used in the training set, reached the coefficient of determination (Rpred2) values for wood density and MFA of 0.60 and 0.72, respectively. The NIR models for wood chemistry showed Rpred2 values of 0.78 and 0.77 for carbohydrates and lignin, respectively. Models for the G-, S- and H-type lignin had Rpred2 values between 0.58 and 0.86. In addition, we developed a prediction model for the determination of tension wood distribution. According to this model, tension wood was frequently observed in young greenhouse samples, which might explain the higher variation found in the chemical and physical properties of wood in greenhouse-grown compared to field-grown trees. The study also demonstrated that NIR-model estimations in image format can capture spatial variations that are not detectable in bulk analyses of wood properties. Examples of the method applied to greenhouse-grown trees highlight the efforts to develop NIR models with good prediction accuracies based on high-resolution data.

From an economic and environmental perspective, the use of less chemicals in the production of cellulose nanofibrils (CNFs) is advantageous. In this study, we investigated the oxidation (TEMPO/NaClO2/NaClO, pH 6.8) of softwood (SW) particles with varying amounts of TEMPO (16, 8 or 0 mg g−1 of wood). Following, TEMPO-oxidized SW nanofibrils (TO-SWNFs) were obtained by nanofibrillation and their size, morphology, and crystallite size were assessed. Hydrogel networks of TO-SWNFs were prepared and mechanical properties were measured in dH2O and phosphate buffered saline (PBS) to compare their performance for possible biomedical applications such as wound dressings. The results reveal that the presence of TEMPO is of importance for TO-SWNF network properties, presenting higher eq. H2O absorption (≈2500 %) and elongation at break (≈10 %) with good wet strength (≈180 kPa). In addition, a decrease in use of TEMPO catalyst from 16 to 8 mg g−1 of wood is possible, without detrimental effects on hydrogel network properties (dH2O absorption ≈ 2000 %, elongation at break ≈ 13 %, wet strength ≈ 190 kPa) related to applications as wound dressings. 

Wood of broad-leaf tree species is a valued source of renewable biomass for biorefinery and a target for genetic improvement efforts to reduce its recalcitrance. Glucuronoxylan (GX) plays a key role in recalcitrance through its interactions with cellulose and lignin. To reduce recalcitrance, we modified wood GX by expressing GH10 and GH11 endoxylanases from Aspergillus nidulans in hybrid aspen (Populus tremula L. × tremuloides Michx.) and targeting the enzymes to cell wall. The xylanases reduced tree height, modified cambial activity by increasing phloem and reducing xylem production, and reduced secondary wall deposition. Xylan molecular weight was decreased, and the spacing between acetyl and MeGlcA side chains was reduced in transgenic lines. The transgenic trees produced hypolignified xylem having thin secondary walls and deformed vessels. Glucose yields of enzymatic saccharification without pretreatment almost doubled indicating decreased recalcitrance. The transcriptomics, hormonomics and metabolomics data provided evidence for activation of cytokinin and ethylene signalling pathways, decrease in ABA levels, transcriptional suppression of lignification and a subset of secondary wall biosynthetic program, including xylan glucuronidation and acetylation machinery. Several candidate genes for perception of impairment in xylan integrity were detected. These candidates could provide a new target for uncoupling negative growth effects from reduced recalcitrance. In conclusion, our study supports the hypothesis that xylan modification generates intrinsic signals and evokes novel pathways regulating tree growth and secondary wall biosynthesis. 

Background: Forest geneticists typically use provenances to account for population differences in their improvement schemes; however, the historical records of the imported materials might not be very precise or well-aligned with the genetic clusters derived from advanced molecular techniques. The main objective of this study was to assess the impact of marker-based population structure on genetic parameter estimates related to growth and wood properties and their trade-offs in Norway spruce, by either incorporating it as a fixed effect (model-A) or excluding it entirely from the analysis (model-B). Results: Our results indicate that models incorporating population structure significantly reduce estimates of additive genetic variance, resulting in substantial reduction of narrow-sense heritability. However, these models considerably improve prediction accuracies. This was particularly significant for growth and solid-wood properties, which showed to have the highest population genetic differentiation (QST) among the studied traits. Additionally, although the pattern of correlations remained similar across the models, their magnitude was slightly lower for models that included population structure as a fixed effect. This suggests that selection, consistently performed within populations, might be less affected by unfavourable genetic correlations compared to mass selection conducted without pedigree restrictions. Conclusion: We conclude that the results of models properly accounting for population structure are more accurate and less biased compared to those neglecting this effect. This might have practical implications for breeders and forest managers where, decisions based on imprecise selections can pose a high risk to economic efficiency.

Drought is a major factor affecting crops, thus efforts are needed to increase plant resilience to this abiotic stress. The overlapping signaling pathways between drought and cell wall integrity maintenance responses create a possibility of increasing drought resistance by modifying cell walls. Here, using herbaceous and woody plant model species, Arabidopsis and hybrid aspen, respectively, we investigated how the integrity of xylan in secondary walls affects the responses of plants to drought stress. Plants, in which secondary wall xylan integrity was reduced by expressing fungal GH10 and GH11 xylanases or by affecting genes involved in xylan backbone biosynthesis, were subjected to controlled drought while their physiological responses were continuously monitored by RGB, fluorescence, and/or hyperspectral cameras. For Arabidopsis, this was supplemented with survival test after complete water withdrawal and analyses of stomatal function and stem conductivity. All Arabidopsis xylan-impaired lines showed better survival upon complete watering withdrawal, increased stomatal density and delayed growth inhibition by moderate drought, indicating increased resilience to moderate drought associated with modified xylan integrity. Subtle differences were recorded between xylan biosynthesis mutants (irx9, irx10 and irx14) and xylanase-expressing lines. irx14 was the most drought resistant genotype, and the only genotype with increased lignin content and unaltered xylem conductivity despite its irx phenotype. Rosette growth was more affected by drought in GH11- than in GH10-expressing plants. In aspen, mild downregulation of GT43B and C genes did not affect drought responses and the transgenic plants grew better than the wild-type in drought and well-watered conditions. Both GH10 and GH11 xylanases strongly inhibited stem elongation and root growth in well-watered conditions but growth was less inhibited by drought in GH11-expressing plants than in wild-type. Overall, plants with xylan integrity impairment in secondary walls were less affected than wild-type by moderately reduced water availability but their responses also varied among genotypes and species. Thus, modifying the secondary cell wall integrity can be considered as a potential strategy for developing crops better suited to withstand water scarcity, but more research is needed to address the underlying molecular causes of this variability. 

Thermographic measurement of lumber moisture content in a progressive kiln This report presents the results of the work carried out in the project "Development of industrial thermal camera measurement for energy-efficient control of wood drying", a project funded by the Kamprad Family Foundation. The project developed, implemented, and evaluated an industrial measurement system for real-time determination of moisture content and moisture distribution in wood during an ongoing drying process. The work included the technical development of a measurement setup for feedback-type progressive kilns, the development of prediction models for wood moisture content, and the development of associated software. The measurement technology was based on thermographic images collected with a thermal camera mounted in the attic space above the passing lumber stacks, as well as information on the properties of the drying air. With knowledge of the wood's temperature state in combination with air temperature and humidity, the drying process could be monitored and evaluated in real time. The software for processing thermographic data, including an operator interface, was installed on a regular desktop computer in the operator room. During the project period, the measurement system was in continuous operation for about one year with only a few short interruptions for maintenance, system updates, and unplanned power outages. Relatively simple instrument maintenance was carried out about two to three times per year. The software's operator interface presented real-time thermographic images of the passing wood and diagrams of the wood's moisture content and distribution. Data collected was continuously and saved to enable long-term analysis. The conclusion is that the measurement system is a useful tool to estimate the moisture content, moisture distribution and inspect the kiln. This information can be used by the drying operator to assess the progress of the drying process and to manually correct the process. Since the measurements were carried out continuously and without either disturbing the production or requiring any extra manual handling by personnel, the measurement system can be considered to meet the requirements of being both non-contact and automatic. The measurement system offered a new way to control the drying process in a progressive lumber kiln with the goal of less over-drying, lower energy consumption, better quality and yield. The method has the potential to replace manual measurements, thus improving worker safety.

The surface temperature of a drying wooden board is strongly related to the drying process. However, it is relatively difficult to determine the surface temperature accurately during drying. In this paper, an experimental setup for analyzing the wood surface during drying by thermal imaging as well as dry and wet-bulb temperature reference surfaces was tested. Spruce sapwood samples were dried in various climates and evaluated with respect to both mass loss and surface temperature. The experimental setup enabled both qualitative and quantitative analysis of the wood drying process. The results showed that thermal imaging enabled a detailed view of the drying progression. The distinct correlation between surface temperature and mass change showed that an accurate determination of a basic, often considered, and difficult-to-determine drying potential is possible. © 2022 The Author(s).