Anni Harju

Background pollination in Pinus sylvestris seed orchards

The proportion of background pollen grains in the seed crops of two Pinus sylvestris seed orchards in Central Finland was estimated with the aid of multilocus allozyme markers. The orchards studied were more than 30 years old and in full pollen production. For the bulked seed crops of the seed orchard with southern clones the estimated average of background pollination over four years was 26%. There were statistically significant differences between years. No significant heterogeneity in the degree of background pollination between clones was found. Among single ramets there was significant heterogeneity in the estimated contamination rates, but the variation was not related to position in the orchard. For the seed orchard with northern clones the bulked seed crop was studied only for one year and the level of background pollination was found to be 33 %. These estimates are fairly high, but lower than for many other orchards. Background pollination at this level will cause losses in expected genetic gains...

Genetic Variation in the Decay Resistance of Siberian Larch (Larix sibirica Ledeb.) Wood

Summary The aim of the study was to estimate the degree of genetic determination in the decay resistance of Siberian larch (Larix sibirica Ledeb.) wood and its correlation to other wood traits. The wood samples were taken from 25-year-old grafted seed orchard clones with an increment core borer, dried, weighed, and subjected to a laboratory decay test using a modified method based on the standardised EN 113 method. One brown rot fungus, Coniophora puteana (Schum. ex Fr.) Karst., was used as the decaying organism. The advantages of the method were the savings in time, the possibility to study standing trees, and the potential for screening large numbers of samples at reasonable costs. The clonal repeatability was used to estimate the degree of genetic determination. The genetic determination appeared to be stronger for decay resistance than for growth characteristics or heartwood formation, but weaker than for wood density or latewood formation. Decay resistance and the growth characteristics did not correlate.

Genetic comparison of natural and nursery grown seedlings of Pinus sylvestris using allozymes

Genetic changes at allozyme loci during the transition from the seed to the seedling stage were studied in a natural stand, where juvenile mortality is high, and in a nursery, where mortality is lower. The seed lots were from a natural stand and a seed orchard of Pinus sylvestris in Central Finland. From both seed lots bare‐rooted and containerized seedlings were produced in a nursery. Both seed lots were found not to be inbred as measured by fixation indices at allozyme loci. Correspondingly, neither natural stand nor nursery grown seedlings showed evidence of inbreeding. We observed allelic frequency differences between the seed lot and seedlings of natural regeneration at two loci. There was only one allelic frequency change between the seed lots and the bare‐rooted seedling populations, and no differences between the seed lots and the containerized seedlings. This is in accordance with the hypothesis that less selection takes place in the nursery than in the natural stands.

FT-NIR spectroscopy in predicting the decay resistance related characteristics of solid Scots pine (Pinus sylvestris L.) heartwood

Abstract FT-NIR spectroscopy equipped with a fiber optic probe was used to predict the mass loss caused by a brown-rot fungus (Coniophora puteana) in Scots pine heartwood. Because decay tests are impractical for generating reference data for the calibration of prediction models, the possibilities of using the concentration of heartwood extractives as a reference variable instead of mass loss was studied. The material investigated covered a wide range of natural variation in durability and diffuse reflectance infrared Fourier transform spectra were recorded from the cross section of 41 pines. The partial least square (PLS) regression models were found to be satisfactory for prediction of the mass loss and the concentration of extractives (total phenolics, resin acids, pinosylvin and pinosylvin monomethyl ether). It was concluded that FT-NIR spectroscopy has the potential to become a tool for the decay resistance grading of Scots pine heartwood timber, especially if the prediction models will be based on heartwood extractives.

Comparing the Effect of Chemical and Physical Properties on Complex Electrical Impedance of Scots Pine Wood

Summary This study examined the effects of physical (moisture content, water content and wood density) and chemical properties (concentration of phenolics and resin acids) on the electrical properties of Scots pine (Pinus sylvesteris L.) wood specimens. Complex impedance was measured from heartwood and sapwood specimens using frequencies between 5 kHz and 1 MHz. Significant correlation between density and electrical properties was found at high frequencies with sapwood specimens in which the extractive content was low. Moisture content had an effect on electrical properties over the whole frequency range. Electrical properties of heartwood samples with high extractive content were differently affected by the chemical and physical properties. Electrical properties were sufficient to distinguish between the samples from the brown-rot resistant and susceptible Scots pine trees.

Knotwood as a window to the indirect measurement of the decay resistance of Scots pine heartwood

Abstract There is wide variation in the extractive content and decay resistance of Scots pine (Pinus sylvestris L.) heartwood. The heartwood is not visible in standing trees and only poorly visible in timber. Therefore, it is difficult to identify extractive-rich trees, and consequently the most decay-resistant heartwood. On the other hand, knots are clearly visible in standing trees and timber. In the present paper we studied the possibility of measuring the decay resistance of Scots pine heartwood indirectly on the basis of the extractive concentration of knotwood. The material investigated consisted of 40 felled trees with a wide between-tree variation for extractive content and decay resistance of their heartwood. The extractive content of knotwood was found to be four- to five-fold higher than that of heartwood. Statistically significant correlations were found between the mass loss of heartwood and the concentrations of total phenolics and stilbenes in knotwood (r=-0.54, P<0.001 and r=-0.40, P=0.011, respectively), and for the concentration of total phenolics (r=0.42, P=0.008) and stilbenes (r=0.39, P=0.012) between heartwood and knotwood. We suggest further development of this technique in the context of rapid industrial screening of durable pine heartwood.

Decay resistance, extractive content, and water sorption capacity of Siberian larch (Larix sibirica Lebed.) heartwood timber

Abstract The aim of this study was to find chemical or physical properties of Siberian larch heartwood timber that correlate with the variation in decay resistance. Juvenile heartwood from 24-year-old grafts of 15 clones was exposed to three brown-rot fungi according to the standard in vitro decay test (European standard EN 113). The mass losses caused by the brown rot fungi Coniophora puteana, Poria placenta, and Gloeophyllum trabeum were 20%, 28% and 17% of the dry mass, respectively. The average mass loss over the three fungi had a strong negative correlation with the concentration of taxifolin (r=–0.673, P=0.006), as well as with the concentration of total phenolics determined by the Folin-Ciocalteu assay (r=–0.677, P=0.006). Thus, the concentration of flavonoids is a promising property for indirect measurement of the decay resistance of Siberian larch timber. The most abundant heartwood extractives, arabinogalactans, had a non-significant relationship with the decay resistance, but their concentration correlated positively with the capacity of the wood to adsorb water (r=0.736, P=0.002). The hygroscopic properties of the wood or the wood density were not associated with the decay resistance.

Developmental Changes in Scots Pine Transcriptome during Heartwood Formation

The Scots pine heartwood formation takes place in the summer and is marked by programmed cell death. Scots pine (Pinus sylvestris L.) wood is desired in woodworking industries due to its favorable timber characteristics and natural durability that is contributed by heartwood extractives. It has been discussed whether the Scots pine heartwood extractives (mainly stilbenes and resin acids) are synthesized in the cells of the transition zone between sapwood and heartwood, or if they are transported from the sapwood. Timing of heartwood formation during the yearly cycle has also not been unambiguously defined. We measured steady-state mRNA levels in Scots pine transition zone and sapwood using RNA sequencing. Year-round expression profiles of selected transcripts were further investigated by quantitative RT-PCR. Differentially accumulating transcripts suggest that, of the Scots pine heartwood extractives, stilbenes are synthesized in situ in the transition zone and gain their carbon-skeletons from Suc and triglycerides. Resin acids, on the other hand, are synthesized early in the spring mainly in the sapwood, meaning that they must be transported to the heartwood transition zone. Heartwood formation is marked by programmed cell death that occurs during the summer months in the transition zone.

Stilbene impregnation retards brown-rot decay of Scots pine sapwood

Abstract Stilbenes are abundant in the heartwood of Scots pine (Pinus sylvestris L.) and are known to have strong antifungal efficiency. In this study, Scots pine sapwood blocks were impregnated with crude heartwood extract containing the stilbenes pinosylvin (PS) and the pinosylvin monomethyl ether (PSM). Impregnated blocks were submitted to brown-rot fungi, Coniophora puteana, Gloeophyllum trabeum, and Rhodonia (Poria) placenta, and fungal growth test and decay test were performed. Both tests showed that the impregnation with a high concentration of stilbenes (60 mg g-1 dry wood) significantly suppressed the growth of fungi and slowed down the decay process of wood blocks, especially in case of G. trabeum. However, chemical analysis showed that PS and PSM were degraded by all the three types of fungi, obviously via modification to resveratrol and methylresveratrol. Rhodonia placenta displayed the fastest rate of degradation. Thus, impregnation with biodegradable stilbenes could be a viable alternative for wood preservation only in service situations with low or transient risk of decay.

Study of stilbene and resin acid content of Scots pine heartwood by electrical impedance spectroscopy (EIS)

Abstract Scots pine (Pinus sylvestris L.) heartwood samples were measured with electrical impedance spectroscopy (EIS) at frequency range 1 Hz–10 MHz in green and relative humidity (RH) 65% conditioned moisture content (MC) after oven-drying. Complex impedance parameters were studied in relation to the density, moisture, resin acid and stilbene contents. The measurements were conducted in tangential (T) and longitudinal (L) directions with 36 samples in each analysis. For green MC, there were significant correlations between impedance phase angle and contents of stilbenes and resin acids at frequencies below 400 Hz. For the resin acid content, the strongest correlation with phase-angleT was -0.45 (P<0.01) at 100 Hz. Impedance magnitude correlated significantly with MC throughout the frequency range, e.g., at 10 kHz, r was -0.71 (P<0.001) for L-direction. In moisture conditioned state, the correlation between stilbenes and T-measured phase angle was strongest at 250 Hz, (r=-0.56, P<0.001). Equivalent circuit model of two ZARC-Cole elements in series was fitted for the measurements in green MC. Several model parameters correlated with MC (e.g., R1, L r=-0.64, P<0.001), but only one parameter correlated weakly with stilbene content (R2, T r=0.35, P<0.05). The study shows that EIS has a potential for independent determination of resin acid or stilbene contents and MC for green pine heartwood.