An experimental study on changes in sound absorption capability of spruce (Picea sitchensis), Douglas fir (Pseudotsuga menziesii), and larch (Larix kaempferi) after microwave treatment

This study investigated changes in the sound absorption coefficients of three anatomical sections of cubed spruce (Picea sitchensis), Douglas fir (Pseudotsuga menziesii), and larch (Larix kaempferi) after microwave treatment. Microwave treatment at 1000 W and 2.4 GHz for 20 min increased the sound absorption coefficients (at 2000–5000 Hz) of spruce by 6.9% in the transverse section, 20.0% in the radial section, and 31.7% in the tangential section. The sound absorption coefficients of Douglas fir increased by 28.9% in the transverse section, 19.1% in the radial section, and 50.0% in the tangential section. Larch coefficients increased by 16.7% in the transverse section, 37.2% in the radial section, and 38.8% in the tangential section. The sound absorption coefficients of the softwoods differed according to species and anatomical plane after microwave treatment. It was concluded that changes in the measured sound absorption coefficient indicate alteration in the pore structure of wood, which can affect in turn wood permeability and impregnation. These data will be helpful for predicting the permeability and impregnation of wood after microwave treatment.

Long-term bending properties of cross-laminated timber made from Japanese larch under constant environment

Cross-laminated timber (CLT) has been used extensively in timber construction. CLT panels are typically used in roofs and floors that carry a continuous load, and it is important to examine the long-term loading capacity of CLT. However, studies that focus on the long-term loading capacity of CLT are limited. To this end, we conducted long-term out-of-plane bending tests on seven-layer CLT made from Japanese larch (Larix kaempferi) under constant environmental conditions, investigated creep performance and duration of load, and experimentally analyzed creep rupture behavior. The mean estimated relative creep after 50 years was 1.49. The sample showed a satisfactory resistance to creep as a building material. The duration of load of most of the specimens in this study was shorter than the conventional value of small clear wood specimens. Specimens had a lower duration of load capacity than solid lumber. According to the results of survival analysis, a loading level of 70% or more caused the initial failure of specimens. Creep rupture of most of the specimens occurred at less deflection than displacement at failure in the short-term loading test. Additional studies focusing on the effects of finger joints, transverse layers, and width of a specimen on creep rupture behavior are suggested.

Early Growth Responses of Larix kaempferi (Lamb.) Carr. Seedling to Short-Term Extreme Climate Events in Summer

Extreme climate events such as heat waves, drought, and heavy rainfall are occurring more frequently and are more intense due to ongoing climate change. This study evaluated the early growth performance of one-year-old Larix kaempferi (Lamb.) Carr. seedlings under open-field extreme climate conditions including experimental warming and different precipitation regimes. We recorded the survival rate, root collar diameter, height, biomass, shoot-to-root ratio, and seedling quality index using nine treatments (three temperature levels, i.e., control, warming by 3 °C and by 6 °C, × three precipitation levels, i.e., control, drought, and heavy rainfall) in July and August 2020. The survival rate of seedlings did not differ between treatments, showing high values exceeding 94% across treatments. The measured shoot height was largest under warming by 3 °C and high rainfall, indicating that moderate warming increased seedling height growth in a moist environment. Heavy rainfall decreased stem volume by 21% and 25% under control and warming by 6 °C treatments, respectively. However, drought manipulation using rain-out shelters did not decrease the growth performance. Overall, extreme climate events did not affect the survival rate, biomass, shoot-to-root ratio, and seedling quality index of L. kaempferi. We thus conclude that, regarding growth responses, L. kaempferi seedlings may be resistant to short-term extreme warming and drought events during summer.

Upgrading the fuel properties of hydrochar by co-hydrothermal carbonisation of dairy manure and Japanese larch (Larix kaempferi): product characterisation, thermal behaviour, kinetics and thermodynamic properties

This study investigated co-hydrothermal carbonisation (co-HTC) of dairy manure (DM) and wood shavings from Larix kaempferi, commonly known as the Japanese larch (JL) to enhance the fuel properties of the resulting hydrochar. The JL was mixed with the DM at 25, 50 and 75 wt.% ratios. Co-HTC was conducted at 260 °C for 20 min. The resulting hydrochars were characterised based on the physicochemical properties and the thermal behaviour. Results showed that the hydrochar solid biofuel properties improved as the ratio of JL was increased. The produced hydrochars were in the region of lignite and closed to the region of the coal with increased fixed carbon, carbon contents and lowered H/C and O/C ratios. Hydrochar with ash content of 7.2 ± 0.5% was obtained at 75 wt.% JL. In addition, the HHV of hydrochar increased remarkably to 26.4 ± 0.02 MJ/kg as the mass ratio of the JL was increased. The surface morphology of the hydrochars were altered and became distinct while the specific surface area (SSA) and the total pore volume (TPV) of the hydrochars increased at increasing the mass ratio of the JL. The surface functional groups were also altered by the co-HTC process. A decline in the combustion performance was observed after the HTC process but improved at 75 wt.% JL after the co-HTC process. The kinetic analysis also revealed that the activation energy decreased after the HTC process but increased to a higher value at 50 wt.% JL after the co-HTC process. Therefore, hydrochar production by co-HTC of DM and JL has proved to be an effective and promising solid biofuel source. Graphical abstract

Embryogenic callus induction from immature zygotic embryos and genetic transformation of Larix kaempferi 3x Larix gmelinii 9

To date, there are few reports of the successful genetic transformation of larch and other conifers, mainly because it is difficult to transform and integrate exogenous genes. In this study, hybrid larch Larix kaempferi 3x Larix gmelinii 9 cones were collected on June 27, July 1, July 4, July 7 and July 16, 2017. Embryogenic callus induction was studied using a combination of different plant growth regulators and concentrations. The results showed that July 1 was the best stage; the highest induction rate was 10.83%, which cultured in BM medium (Button medium, which formula was listed in S1 Table) with 1.0 mg/L 2,4-D (2,4-dichlorophenoxyacetic acid) and 0.2 mg/L KT(kinetin). When cultured on a proliferation medium for 12 days, proliferation was the fastest, reaching 323.08%, which could also maintain the freshness and vitality. The suitable pre-culture medium for somatic embryogenesis was 1/4 BM medium containing 10 g/L inositol and 60 g/L sucrose. The combination of 45 mg/L ABA (abscisic acid) and 75 g/L PEG4000 (Polyethyene glycol 4000) could promote the number of somatic embryos, and reached the maximum, 210 140 per 1 g FW. The genetic transformation was carried out by the Agrobacterium-mediated transformation method with embryogenic callus cultured for 12 days. The results showed the optimal OD600 of the infection solution(suspension of A. tumefaciens) was 0.5, co-culture time was 2 days, and screening concentration of Hyg (hygromycin B) was 4 mg/L. In this study, the transformation rate of resistance callus was 32.1%. It provides a reference for low genetic transformation efficiency of larch at present. This study could be beneficial for the innovation and breeding of larch by genetic engineering and provides a certain basis for rapid propagation of excellent larch germplasm resources and genetic engineering breeding of larch and other conifers.

Pedigree Reconstruction and Spatial Analysis for Genetic Testing and Selection In A Larix Kaempferi (Lamb.) Carrière Plantation

Background: Larix kaempferi is one of the major timber species in Northeast Asia. Demand for the reforestation of the species is rising in South Korea due to an increase in large timber production and utilization. However, progeny trials for the species have not been explored, making it challenging to foster advanced generations of tree improvement. In the present study, genetic testing and selection for diameter growth were conducted using pedigree reconstruction and phenotypic spatial distribution analysis in a plantation of L. kaempferi. The aim of the present study was to select the superior larch individuals using the pedigree reconstruction and phenotypic spatial distribution to substitute progeny trials. The plantation of seed orchard crops was established in 1990 and one-hundred and eighty-eight trees were selected as the study material. Genetic variation was investigated first to validate its adequacy as breeding material. Genetic testing was carried out using a model considering pedigree information and spatial autoregression of the phenotypes. The major environmental effects on growth were assessed to understand the site characteristics where the breeding materials were located.Results: The expected heterozygosity of the mother trees and offspring were 0.672 and 0.681 presenting the corresponding level of genetic variation between two groups. The pedigree reconstruction using maternity analysis assigned one to six progenies to ninety-two candidate mothers. The accuracy of genetic testing was exceedingly increased with the animal model considering AR1⊗AR1 structure compared to the animal model only. The estimated genetic variance of the former was 9.086 whereas that of the latter was 4.9E-5. The predicted breeding values of the offspring were ranged from -5.937 to 5.655 and the estimated heritability of diameter growth was 0.344. Shifts in the effects of the factors were detected using geographically weighted regression analysis, which provided information on the post-sectioning of the plantation. Conclusions: The genetic testing approach based on pedigree reconstruction and phenotypic spatial distribution analysis was considered a useful analytical scheme that could replace or supplement progeny trials. Subdivision of the plantation as blocks of the progeny testing was accomplished a posteriori based on the changes of the environmental effects.

Over-Expression of the Cell-Cycle Gene LaCDKB1;2 Promotes Cell Proliferation and the Formation of Normal Cotyledonary Embryos during Larix kaempferi Somatic Embryogenesis

Somatic embryogenesis is an effective tool for the production of forest tree seedlings with desirable characteristics; however, the low initiation frequency and productivity of high-quality mature somatic embryos are still limiting factors for Larix kaempferi (Japanese larch). Here, we analyzed the expression pattern of L. kaempferi cyclin-dependent kinase B 1;2 (LaCDKB1;2) during somatic embryogenesis in L. kaempferi and its relationship with the cell proliferation rate. We also analyzed the effect of LaCDKB1;2 over-expression on somatic embryo quality. The results revealed a positive correlation between LaCDKB1;2 expression and the cell proliferation rate during the proliferation stage. After LaCDKB1;2 over-expression, the proliferation rate of cultures increased, and the number of somatic embryos in transgenic cultures was 2.69 times that in non-transformed cultures. Notably, the number of normal cotyledonary embryos in transgenic cultures was 3 times that in non-transformed cultures, indicating that LaCDKB1;2 not only increases the proliferation of cultures and the number of somatic embryos but also improves the quality of somatic embryos. These results provide insight into the regulatory mechanisms of somatic embryogenesis as well as new Larix breeding material.

Investigation of electrical characteristics using various electrodes for evaluating the moisture content in wood

Electrical resistance and resistivity were measured with various types of electrodes to evaluate the moisture content of wood. The conventional two-pin method, electrically conductive fabrics, and multi-pin electrodes were used to measure the electrical resistance of Japanese larch (Larix kaempferi) wood, and a four-pin probe was used for resistivity measurements. The resistance in the longitudinal direction measured with the two-pin electrode was slightly affected by the dimensions of the wood sample, whereas the resistance measured with the conductive fabric and multi-pin electrodes was clearly affected by the end surface area in contact with the electrode and the length between electrodes. The resistivity calculated from the relationship between the electrical resistance and sample dimensions also showed differences based on the sample dimensions. The least squares regression model trained with the resistance data based on the two-pin method predicted the moisture content with a high coefficient of determination of 0.986. The four-pin probe produced the most stable resistivity regardless of the sample dimensions, making it a feasible approach for the moisture evaluation of large wood members.