Andrey Pranovich

The ecophysiology of the Norway spruce (Picea abies (L.) Karst.) trees that were used by three-toed woodpeckers (TTW) (Picoides tridactylus) for their sap-feeding activities were investigated. The pilot study was conducted in southern Finland (61°15′ N, 25°00′ E). During April–June 2015, three different tree categories of Norway spruce were selected for monitoring: trees that were frequently used by the TTWs for phloem sap-feeding for several previous years; trees that were only recently used by TTWs for sap-feeding; and control trees that were not used at all for sap-feeding. Phloem sap and phloem tissue samples were frequently extracted from tree trunks and analyzed for the content and composition of nonstructural carbohydrates, phloem sap osmolality, solute, and water content, as well as for the content and composition of secondary metabolites typical for defense reactions in the phloem. Simple crown characteristics were also measured, including tree height, diameter at breast height, and their ratio (slenderness index). According to our results, the TTWs preferred Norway spruce trees that showed advanced spring phenology to feed on, as evidenced especially by the lower ratio of raffinose (typically high during the winter months) to total soluble sugars of phloem tissues as compared to non-used control trees. The lower slenderness index of the trees chosen by the TTWs indicates low canopy competition pressure with good access to light (i.e., the sun heats the trunks well in spring). There were no differences in the phloem osmolality or solute content between the used or unused control trees. The trees used by the TTWs had significantly higher concentrations of antioxidant phenolic (+)-catechins and stilbene glycosides in phloem tissue, and the stilbene content was also higher in the extracted sap. The phenolics content of the phloem tissue had a clear seasonal trend, being the highest in the early spring and lower towards the onset of the cambial growth processes. The phloem sap is rich in antioxidants and soluble sugars that are potentially beneficial for the TTWs, but more quantitative research is needed to explore the importance of the sap properties to TTWs.

The physical, mechanical, and chemical properties of both stem wood and knot wood were investigated from two subfossil Scots pine (Pinus sylvestris L.) trunks retrieved from a lake in Finnish Lapland, dated to 404–486 CE and to 1318–1444 CE. Both the stem wood and the knot wood of the younger trunk had higher moisture content, lower density, and lower strength properties in comparison to the older trunk. The ash content of the stem wood of the younger trunk was lower, but the ash content of the knot wood was higher than that of the older trunk. Due to the degradation that occurred over time, all the values of physical and mechanical properties were lower compared to typical values of recently grown Scots pine wood. The chemical composition of both stem wood samples was close to the composition of the recently grown wood, and the only exception was the small decrease of the cellulose and hemicellulose in the subfossil samples. The bulk extractives were well-preserved, but terpenes and fatty acids underwent transformation, resulting in more stable compounds. The SWOT analysis (strengths, weaknesses, opportunities, and threats) showed pros and cons for the productization of subfossil wood, with the branding value of an ancient material being the potential enabler in developing commercial niche uses.

Lignans are bioactive compounds that are especially abundant in the Norway spruce (Picea abies L. Karst.) knotwood. By combining a variety of chromatographic, spectroscopic and imaging techniques, we were able to quantify, qualify and localise the easily extractable lignans in the xylem tissue. The knotwood samples contained 15 different lignans according to the gas chromatography-mass spectrometry analysis. They comprised 16% of the knotwood dry weight and 82% of the acetone extract. The main lignans were found to be hydroxymatairesinols HMR1 and HMR2. Cryosectioned and resin-embedded ultrathin sections of the knotwood were analysed with scanning transmission X-ray microscopy (STXM). Cryosectioning was found to retain only lignan residues inside the cell lumina. In the resin-embedded samples, lignan was interpreted to be unevenly distributed inside the cell lumina, and partially confined in deposits which were either readily present in the lumina or formed when OsO₄ used in staining reacted with the lignans. Furthermore, the multi-technique characterisation enabled us to obtain information on the chemical composition of the structural components of knotwood. A simple spectral analysis of the STXM data gave consistent results with the gas chromatographic methods about the relative amounts of cell wall components (lignin and polysaccharides). The STXM analysis also indicated that a torus of a bordered pit contained aromatic compounds, possibly lignin.

Ground spruce wood was extracted with pressurized hot water in an accelerated solvent extractor (ASE) at 170°C during 20, 60, and 100 min. Released aromatic substances (from 2.2 to 2.5% on wood basis) were isolated on XAD-7 resin and fractionated into lignin, oligomeric aromatic substances (OAS), and compounds insoluble in methanol (IMC). The separated aromatic fractions, and the ground wood before and after extraction, were characterized by physico-chemical methods (GC, GC-MS, HPLC-SEC, TG, DSC). The major part of the aromatic substances was oligomeric aromatic substances (OAS). This fraction increased significantly with the extraction time, while the yield of dissolved lignin increased only slightly with extraction time. Isolated lignins had a lower molar mass and differed considerably from spruce milled wood lignin (MWL). The isolated lignins were more stable against oxidative thermodegradation than spruce MWL. The UV-extinction coefficients at 280 nm were lower for the isolated lignins than for MWL.

Ground spruce sapwood was extracted with pressurised hot water with addition of different amounts of sodium bicarbonate (NaHCO₃) to find optimal pH conditions for extraction of hemicelluloses, especially of galactoglucomannans (GGMs). The extractions were carried out in an accelerated solvent extractor (ASE) at 170°C. When extraction was carried out with 2.5 mM NaHCO₃during 60–100 min extraction time (end-pH 3.9), more than 60% of the total extracted substances were hemicellulose-derived carbohydrates. Under these conditions, approximately 80% of the extracted carbohydrates were from GGMs (13% b.o. wood). At higher concentrations of NaHCO₃, the yield of carbohydrates, especially those derived from GGMs, decreased. Hydrolytic depolymerisation of hemicelluloses occurring during extraction with plain water was largely inhibited in the presence of 2.5–5 mM NaHCO₃. The hydrolytic deacetylation of GGM was diminished at low NaHCO₃concentrations but increased dramatically at higher NaHCO₃concentrations. It can be concluded that 2.5–5 mM NaHCO₃giving an end-pH value of 4 is better for GGM isolation than plain water.

Sapwood chips and ground wood of spruce have been extracted with pressurised pure water in an accelerated solvent extractor at temperatures from 100 to 180°C. The water extracts were freeze-dried, weighed, and analysed for carbohydrates by acid methanolysis followed by GC determination of monomeric sugars. Lignin was determined by measuring UV absorption and acetyl groups by HPLC after alkaline hydrolysis. Average molar masses of hemicelluloses in water extracts were determined by HPSEC-MALLS after filtration. Typically, approximately 70% of the total weighed extracts were composed of carbohydrates derived from hemicelluloses. Approximately 75% of the extracted carbohydrates were from galactoglucomannan (GGM). Other extracted substances were xylans, arabinogalactans, lignin and acetic acid. As much as 80–90% of the GGM in the wood, i.e., approximately 15% based on the original wood, was extracted from ground wood at 170–180°C for an extraction time of 1 h. The yields from chips were lower: approximately 60% from that of ground wood. The hemicelluloses were partly hydrolysed during the extractions at 160–180°C. Xylans and arabinogalactans were hydrolysed to a higher extent than GGM. Acetyl groups in GGM were also partly hydrolysed, which resulted in lower GGM solubility. A key factor for achieving a high yield of high-molar mass GGM is an optimised pH profile in order to minimise hydrolysis of acetyl groups and hydrolytic cleavage of GGM chains.