Volume 76, Issue 2 - Special issue: Celebrating 75 years of Holzforschung; Issue Editor: Lennart Salmén

Wood science covers in particular the areas of the formation and composition as well as the chemical, biological and physical-mechanical properties of wood. First comprehensive studies have already been published in the last century. Detailed knowledge of wood is required for the processing of wood, the production of wood-based materials, and the utilization of wood and wood-based materials as buildings and various other products such as furniture. This review gives a brief overview on the progress in wood chemistry, wood biology (including photosynthesis and biodeterioration), and physical-mechanical properties of wood and wood-based materials. These fundamentals are also essential for understanding technological processes and product development.

Globally, there has been an increasing amount of wood harvested from younger, fast-growing trees derived from plantation forests. As a consequence, producers and industrial consumers of wood products are becoming increasingly concerned with not only growth rates, but specific wood attributes that affect processing efficiencies and final product quality. Intra-ring checking is a problem that down-grades an unacceptably high proportion of radiata pine clearwood. Methods of identifying trees prone to this undesirable behaviour have been relatively destructive and time consuming, and from a breeding perspective, to date, there is no reliable method of predicting which selected progeny will later show a propensity to check. Using 120, 7-year-old Pinus radiata clones sampled from a common site, displaying difference in the propensity to form intra-ring checks, a GC/MS-based global metabolic profiling technique was employed to demonstrate that metabolomics can be used to accurately identify the checking phenotype. Metabolic profiling coupled with statistical tests was then used to develop models with greater than 90% efficiency to predict the intra-ring checking phenotype. Moreover, an inspection of unique metabolites contributing to the models indicated that coniferin, which is often found as a storage compound in rays, is a strong indicator of intra-ring checking, and indeed those genotypes that displayed the propensity to check inherently had a greater number of ray cells per unit area.

Hydroxycinnamoyl shikimates were reported in 2005 to be intermediates in monolignol biosynthesis. 3-Hydroxylation of p -coumarate, originally thought to occur via coumarate 3-hydroxylase (C3H) from p -coumaric acid or its CoA thioester, was revealed to be via the action of coumaroyl shikimate 3′-hydroxylase (C3′H) utilizing p -coumaroyl shikimate as the substrate, itself derived from p -coumaroyl-CoA via hydroxycinnamoyl-CoA: shikimate hydroxycinnamoyltransferase (HCT). The same HCT was conjectured to convert the product, caffeoyl shikimate, to caffeoyl-CoA to continue on the pathway starting with its 3- O -methylation. At least in some plants, however, a more recently discovered caffeoyl shikimate esterase (CSE) enzyme hydrolyzes caffeoyl shikimate to caffeic acid from which it must again produce its CoA thioester to continue on the monolignol biosynthetic pathway. HCT and CSE are therefore monolignol biosynthetic pathway enzymes that have provided new opportunities to misregulate lignification. To facilitate studies into the action and substrate specificity of C3H/C3′H, HCT, and CSE enzymes, as well as for metabolite authentication and for enzyme characterization, including kinetics, a source of authentic substrates and products was required. A synthetic scheme starting from commercially available shikimic acid and the four key hydroxycinnamic acids ( p -coumaric, caffeic, ferulic, and sinapic acid) has been developed to provide this set of hydroxycinnamoyl shikimates for researchers.

Various phenomena in living physiological systems are conducted on the hydrated conditions, and in many cases, they do not work in a dry state. Imaging mass spectrometry is one of the direct detection methods scanning the sample surface with some focused and pulsed energy and analysing the sputtered components. However, under the high vacuum conditions required for usual imaging mass spectrometry, the sample surface is rapidly dried. It is difficult for the target cell to survive, and the original situation are lost soon. Here, the combination of a freeze-fixation and a cryo sample stage is a promising method to do mass spectrometry while maintaining the original situation. By rapidly freezing the cells, the momentary situation as a living cell is fixed. The situation in a living cell can be captured as still images by cryo imaging mass spectrometry. This mini-review introduces the outline of imaging mass spectrometry especially for low molecular weight components and recent results for frozen-hydrated samples by cryo secondary ion mass spectrometry.

Lignosulfonates (LSs) are by-products of the pulp and paper industry from pulping of lignocellulosic biomass according to the sulfite process. This renewable material already plays a role in low-value applications, such as binding agents for fuel, pellets, as a feed additive, or as a dispersant. Another possible field of application of this technical lignin type is agriculture. It is known that this eco-friendly and cheap material can improve soil quality, fertilizer efficacy and replace or decrease the use of potentially (eco)toxic organic or inorganic substances. The use of LS in agriculture and five main strategies for the implementation of LS in soil are discussed in this review: LS as a complexing agent with micronutrients, co-pelleting of LS with (macro)nutrients, capsule formation with LS for coating of fertilizers or pesticides, LS as a biostimulant, and ammonoxidation of LS. All five ways can be beneficial in fertilizer-related applications, either to slow down the release of nutrients or pesticides, to substitute harmful chemicals, or to inhibit nitrification and modify fertilizer behaviour. Nevertheless, application and long-time studies are often missing, and more research is required for generating products that are economically competitive to commercial bulk products.

Eucalyptus ( Eucalyptus globulus ) cellulose was isolated from wood powder by dewaxing, delignification, and subsequent 4% NaOH extraction. 2,2,6,6-Tetramethyl-piperidine-1-oxyl (TEMPO)-oxidized eucalyptus celluloses were prepared from never-dried eucalyptus cellulose (EC) in yields of 96% and 72% (based on the dry weight of EC) when oxidized with NaOCl of 5 and 10 mmol/g-EC, respectively. Their carboxy contents were 1.4 and 1.8 mmol/g, respectively, when determined by conductivity titration. The crystallinity of cellulose I for EC decreased by TEMPO-mediated oxidation, showing that the originally crystalline region in EC was partly converted to disordered regions by TEMPO-mediated oxidation. Correspondingly, the relative signal area of C6‒OH/C1 with the trans-gauche ( tg ) conformation attributed to crystalline cellulose I in the solid-state 13 C NMR spectrum of EC decreased from 0.42 to 0.34 by TEMPO-mediated oxidation with NaOCl of 10 mmol/g-EC. TEMPO-oxidized EC prepared with NaOCl of 10 mmol/g-EC was almost completely converted into individual TEMPO-oxidized EC nanofibrils (TEMPO-ECNFs) of homogeneous widths of ∼3 nm widths and lengths of >1 μm by mechanical disintegration in water. However, the TEMPO-ECNFs contained many kinks and had uneven surfaces, probably owing to significant damage occurring on the surface cellulose molecules of crystalline cellulose microfibrils during TEMPO-mediated oxidation.

Buckling tests were conducted using slender specimens of western hemlock. In the tests, the slenderness ratio was varied from 132 to 418 in which elastic buckling was induced, and the values of the critical load for buckling were obtained. When the deflection of the specimen was calculated from the loading-line displacement based on elastica theory, the value of deflection/load initially decreased because the compressive deformation was more dominant than the bending deformation. In contrast, when the load increased, the bending deformation became dominant, and the deflection/load-deflection relation exhibited linearity. These tendencies indicated that the transition from compression to bending was induced around the minimum value of the deflection/load. Therefore, it was recommended to determine the critical load for buckling using the load at the minimum value of the deflection/load where the deflection was calculated from the loading-line displacement.

Construction using timber has seen a resurgence in light of global climate mitigation policies. Wood is a renewable resource, and engineered wood products are proving to be competitive against concrete and steel while having several advantages. However, while the renewable nature of wood in construction is a beneficial property for climate mitigation policies, the process of biodegradation introduces a challenge for service life planning. A review of hazard mapping is presented while developing contemporary hazard maps, occurrence maps and projected hazard maps for 2050 using representative concentration pathways ( RCP ) 2.6 and 8.5. The risk of timber decay is expected to increase in most of Europe as the temperatures rise, with a decrease expected in dryer regions. Termites are likely to experience a range expansion as more areas become suitable, while human activity and an increase in extreme weather events like floods are expected to facilitate dispersion. Marine borer species already present a risk in most European coastal regions; however, the effect of changes in water temperatures are likely to shift the boundaries for individual borer species. Overall, warmer climates are expected to increase the metabolic activity of all of these organisms leading to a general reduction in service life.

Wood has great potential to become a key material for future bio-economy, thanks especially to its intrinsic renewability and CO 2 -storing capacity. Improved functionalization treatments can make wood materials valid substitutes for less ecofriendly ones, expanding and widening their application range. However, further research is needed. This mini-review highlights some of the most recent developments in the design of functional wood materials, critically discussing their current limitations and obstacles to their implementation.