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Background Larch ( Larix gmelinii (Rupr.) Kuzen.) is an important timber and ecological tree species in northern China. Excellent germplasm resources have been acquired through time-consuming traditional breeding. Molecular breeding offers a promising approach to shorten the breeding cycle and achieve genetic improvements more efficiently. MicroRNAs (miRNAs) are non-coding, single-stranded small RNAs that primarily affect plant growth and stress resistance, including drought stress. However, the study of miRNAs in larch under drought stress has not been well explored. Results In this study, to investigate the function of Lol-miR11467 under PEG osmotic stress in larch, embryogenic callus tissue of Larix kaempferi 3 × L. gmelinii 9 was employed as the experimental material, serving as the explants for this study. Lol-miR11467 was transferred into the explants using an Agrobacterium-mediated method to determine the physiological changes and survey gene expression changes in overexpressing Lol-miR11467 cell lines. The results showed that the fresh weight, peroxidase (POD), soluble protein and soluble sugar content of the overexpressing Lol-miR11467 were lower than that of the wild-type, while malondialdehyde (MDA) content increased under PEG osmotic stress. Transcriptome analysis showed that genes associated with phenylpropanoid metabolism, transcription factors, oxidoreductase, plant hormone signal transduction, glucose metabolism and bioprotective macromolecules were mainly downregulated in Lol-miR11467 cell lines. Conclusions Overall, these results indicated that the drought resistance of the overexpressing Lol-miR11467 cell lines was reduced. This study’s findings might provide a foundation for understanding the molecular mechanisms of miRNAs under PEG osmotic stress in larch, potentially contributing to the development of strategies for improving plant resilience to environmental stresses.

Larix principis-rupprechtii is a native tree species in North China with a large distribution; and its harvested timbers can be used for producing wood products. This study focused on estimating and comparing carbon flows and carbon footprints of different harvested wood products (HWPs) from Larix principis-ruppechtii based on the life cycle analysis (from seedling cultivation to HWP final disposal). Based on our interviews and surveys, the system boundary in this study was divided into three processes: the forestry process, the manufacturing process, and the use and disposal process. By tracking carbon flows of HWPs along the entire life cycle, we found that, for one forest rotation period, a total of 26.81 tC/ha sequestered carbon was transferred into these HWPs, 66.2% of which were still stored in the HWP when the rotation period had ended; however, the HWP carbon storage decreased to 0.25 tC/ha (only 0.9% left) in the 100th year after forest plantation. The manufacturing process contributed more than 90% of the total HWP carbon footprint, but it was still smaller than the HWP carbon storage. In terms of the carbon storage and the carbon footprint, construction products had the largest net positive carbon balance compared to furniture and panel products. In addition, HWP are known to have a positive impact on global carbon mitigation because they can store parts of the sequestered carbon for a certain period of time and they have a substitution effect on carbon mitigation. Furthermore, there still exist great opportunities for carbon mitigation from HWPs through the use of cleaner energy and increasing the utilization efficiency of wood fuel.

We had continuously measured soil CO sub(2) efflux (R sub(s)) in a larch forest in northern Japan at hourly intervals for the snow-free period in 2003 with an automated chamber system and partitioned R sub(s) into heterotrophic respiration (R sub(h)) and autotrophic respiration (R sub(r)) by using the trench method. In addition, we applied the soil CO sub(2) concentration gradients method to continuously measure soil CO sub(2) profiles under snowpack in the snowy period and to partition R sub(s) into topsoil (O sub(a) and A horizons) CO sub(2) efflux (F sub(t)) with a depth of 0.13 m and sub-soil (C horizon) CO sub(2) efflux (F sub(c)). We found that soil CO sub(2) effluxes were strongly affected by the seasonal variation of soil temperature but weakly correlated with soil moisture, probably because the volumetric soil moisture (30-40% at 95% confidence interval) was within a plateau region for root and microbial activities. The soil CO sub(2) effluxes changed seasonally in parallel with soil temperature in topsoil with the peak in late summer. On the other hand, the contribution of R sub(r) to R sub(s) was the largest at about 50% in early summer, when canopy photosynthesis and plant growth were more active. The temperature sensitivity (Q sub(10)) of R sub(r) peaked in June. Under snowpack, R sub(s) was stable until mid-March and then gradually increased with snow melting. R sub(s) summed up to 79 gC m super(-2) during the snowy season for 4 months. The annual R sub(s) was determined at 934 gC m super(-2) y super(-1) in 2003, which accounted for 63% of ecosystem respiration. The annual contributions of R sub(h) and R sub(s) to R sub(s) were 57% and 43%, respectively. Based on the gradient approach, R sub(s) was partitioned vertically into litter (O sub(i) and O sub(e) horizons) with a depth of 0.01-0.02 m, topsoil and sub-soil respirations with proportions of 6, 72 and 22%, respectively, on an annual basis. The vertical distribution of CO sub(2) efflux was consistent with those of soil carbon and root biomass.

Somatic embryogenesis (SE) involves complex molecular signalling pathways. Understanding molecular mechanism of SE in Larix leptolepis (L. leptolepis) can aid research on genetic improvement of gymnosperms. Previously, we obtained five LaMIR166a (miR166a precursor) -overexpression embryonic cell lines in the gymnosperm Larix leptolepis. The proliferation rates of pro-embryogenic masses in transgenic and wild-type lines were calculated. Overexpression of the miR166a precursor LaMIR166a led to slower proliferation. When pro-embryogenic masses were transferred to maturation medium, the relative expression of LaMIR166a and miR166a in the LaMIR166a-overexpression lines was higher than in the wild-type during SE, while LaHDZ31–34 expression levels also increased without negative control by miR166, suggesting that regulation of HD-ZIP III by miR166a exits stage-specific characteristics. The key indole-3-acetic acid (IAA) biosynthetic gene Nitrilase of L. leptolepis (LaNIT) was identified and the effects of miR166a on auxin biosynthesis and signalling genes were studied. During SE, LaNIT, Auxin response factor1 (LaARF1) and LaARF2 mRNA levels and IAA contents were markedly higher in LaMIR166a-overexpression lines, which revealed lower deformity rate of embryos, indicating endogenous IAA synthesis is required for somatic embryo maturation in L. leptolepis. Additionally, the IAA biosynthesis and signalling genes showed similar expression patterns to LaHDZ31–34, suggesting HD-ZIP III genes have a positive regulatory effect on LaNIT. Our results suggest miR166a and LaHDZ31–34 have important roles in auxin biosynthesis and signalling during SE, which might determine if the somatic embryo normally developed to mature in L. leptolepis.

MicroRNAs (miRNAs) are emerging as essential regulators of biological processes. Somatic embryogenesis is one of the most important techniques for gymnosperm-breeding programs, but there is little understanding of its underlying mechanism. To investigate the roles of miRNAs during somatic embryogenesis in larch, we constructed a small RNA library from somatic embryos. High-throughput sequencing of the library identified 83 conserved miRNAs from 35 families, 16 novel miRNAs, and 14 plausible miRNA candidates, with a high proportion specific to larch or gymnosperms. qRT-PCR analysis demonstrated that both the conserved and novel or candidate miRNAs were expressed in larch. Several miRNA precursor sequences were obtained via RACE. We predicted 110 target genes using bioinformatics, and validated 9 of them by 5' RACE. 11 conserved miRNA families including 17 miRNAs with critical functions in plant development and six target mRNAs were detected by qRT-PCR in the larch SE. Stagespecific expression of miRNAs and their targets indicate their possible modulation on SE of larch: miR171a/b might exert function on PEMs, while miR171c acts in the induction process of larch SE; miR397 and miR398 mainly involved in modulation of propagation and transition to single embryo; miR162 and miR168 exert their regulatory function during total SE process, especially during stages 5-8; miR156, miR159, miR160, miR166, miR167, and miR390 might play regulatory roles during cotyledonary embryo development. These findings indicate that larch and possibly other gymnosperms have complex mechanisms of gene regulation involving specific and common miRNAs operating post-transcriptionally during embryogenesis.

The study assessed the sensitivity of 20 provenances of European larch ( Larix decidua Mill.) growing at provenance experimental trials located in lowland (Siemianice) and upland (Bliżyn) climate in Central Poland to air temperature and precipitation, including drought. The measure of the tree’ sensitivity was their radial growth reactions, i.e. changes in the radial growth in years 1971–2015. We found that rainwater supplies in a soil stored in autumn of the previous year, length of the growing season and thermal conditions in its beginning, as well as thermal and moisture conditions of the year of tree ring formation had a significant impact on the wood volume formed by the larches, regardless of their origin and climatic region in which they grew. The degree of homogeneity of tree’ radial growth reactions to precipitation deficit and high temperature was the lowest in a warmer and drier climate in the lowlands in Central Poland. Larch provenances with the lowest and the highest values of drought resilience components (resistance, recovery, resilience, relative resilience of radial growth) originated in different regions of Poland. Greater resistance to drought was observed in larch provenances growing at the trial located in the uplands. The relative resilience index seems to be the most helpful in predicting the future radial growth reactions of the studied provenances, and consequently their viability and survival, as this index showed the highest variability among trees of a given provenance and was most often significantly different between pairs of provenances.

Background In plants, time information is recorded in strictly ordered sequences of development events, resulting in age-associated physiological and morphological differentiation, including clear spatial gradients from the base to the crown within a single tree. However, the molecular mechanisms driving such ontogeny-related differentiation remain largely unknown. Results Based on our newly generated Larix kaempferi (Lamb.) Carr. genome annotation, we identified 307 age-related genes, which were grouped into two expression clusters reflecting opposite temporal trends. Spatial expression analysis further revealed 13 differentially expressed genes along the vertical axis of the tree, suggesting their roles in regulating spatially distinct physiological traits. Yeast one-hybrid and dual-luciferase reporter assays demonstrated that LaAGL2-3b directly binds to the promoters of six genes, including LaAGL2-3a , LaAGL2-3b (self-regulation), and L. kaempferi cycloartenol synthase ( LkCAS1 ). Over-expression of LaAGL2-3 in Arabidopsis thaliana (L.) Heynh. significantly accelerated life cycle progression, supporting its functional involvement in aging-related developmental processes. Conclusions Our results indicate that LaAGL2-3 shows coordinated temporal and spatial expression dynamics with other age-related genes in L. kaempferi . This coordinated pattern offers hypotheses about its potential role within age-associated regulatory processes. The genomic and transcriptomic resources generated here offer a foundation for future functional investigations and for improving our understanding of conifer development and ontogeny.

The prevalence of coniferous trees in the forest landscapes of northeastern Siberia is conditioned by their high frost resistance. The Kajander larch (Larix cajanderi Mayr), which can survive under natural conditions (down to −60 °C) in the cryolithozone of Yakutia, is the dominant forest-forming species. We hypothesise that our study using HPTLC–UV/Vis/FLD, TLC–GC/FID, and GC–MS methods of seasonal features of the lipid profile of Kajander larch tissues will bring us closer to understanding the mechanisms of participation of lipid components in the adaptation of this valuable tree species to the cold climate of the cryolithozone. Rare delta5-unsaturated polymethylene-interrupted fatty acids (∆5-UPIFA) were identified in the fatty acids (FAs) of L. cajanderi shoots, including 18:2(Δ5.9) (taxoleic), 18:3(Δ5.9.12) (pinolenic), and 18:4(Δ5.9.12.15) (coniferonic). It was found that the content of ∆5-UPIFA in L. cajanderi shoots markedly increased (1.5-fold, representing up to 23.9% of sum FAs) during the autumnal transition of trees to dormancy. It was observed that the ranges of low temperatures experienced during the prolonged winter period primarily determined the structural diversity of membrane lipids and their constituent FAs during the cold adaptation of L. cajanderi. The results obtained can be used for the selection of molecular markers of cold tolerance in woody plants, including fruit trees.

Tree species through aboveground biomass and roots are a key factors influencing the quality and quantity of soil organic matter. Our study aimed to determine the stability of soil organic matter in Luvisols under the influence of five different tree species. The study areas were located 25 km north of Krakow, in southern Poland. The study included five tree species - Scots pine ( Pinus sylvestris L.), European larch ( Larix decidua Mill.), pedunculate oak ( Quercus robur L.), beech ( Fagus sylvatica L.) and hornbeam ( Carpinus betulus L.). Forest stands growing in the same soil conditions (Luvisols) with similar geological material (loess) and grain size were selected for the study. We evaluated labile and heavy fractions of soil organic matter (SOM). Additionally, basic physicochemical properties (pH, carbon and nitrogen content, base cation content) were determined in soil samples. The results of our study showed that soils under the influence of coniferous species were characterized by a higher content of carbon of free light fraction (C fLF ) and carbon of occluded light fraction (C oLF ) compared to deciduous species. Similar relationships were found with the nitrogen content of the free light fraction (N fLF ) and nitrogen of occluded light fraction (N oLF ). Higher C MAF and N MAF contents were recorded in soils influenced by deciduous species. The carbon, nitrogen and base cations content positively correlated with the C and N of free light fraction and occluded light fraction. PCA analysis confirmed the connection of C and N of heavy fractions (C MAF and N MAF ) with deciduous species. Our research shows that avoiding single-species conifer stands and introducing admixtures of deciduous species, which increase SOM, is justified in forest management. The selection of suitable species will provide greater stand stability and contribute more to the carbon accumulation in the soil.