Background: Pinus koraiensis is an evergreen tree species with strong cold resistance. However, the transcriptomic patterns in response to cold stress are poorly understood for P. koraiensis. In this study, global transcriptome profiles were generated for P. koraiensis under cold stress (− 20 °C) over time by high-throughput sequencing. Results: More than 763 million clean reads were produced, which assembled into a nonredundant data set of 123,445 unigenes. Among them, 38,905 unigenes had homology with known genes, 18,239 were assigned to 54 gene ontology (GO) categories and 18,909 were assigned to 25 clusters of orthologous groups (COG) categories. Comparison of transcriptomes of P. koraiensis seedlings grown at room temperature (20 °C) and low temperature (− 20 °C) revealed 9842 differential expressed genes (DEGs) in the 6 h sample, 9250 in the 24 h sample, and 9697 in the 48 h sample. The number of DEGs in the pairwise comparisons of 6 h, 24 h and 48 h was relatively small. The accuracy of the RNA-seq was validated by analyzing the expression patterns of 12 DEGs by quantitative real-time PCR (qRT-PCR). In this study, 34 DEGs (22 upregulated and 12 downregulated) were involved in the perception and transmission of cold signals, 96 DEGs (41 upregulated and 55 downregulated) encoding 8 transcription factors that regulated cold-related genes expression, and 27 DEGs (17 upregulated and 10 downregulated) were involved in antioxidant mechanisms in response to cold stress. Among them, the expression levels of c63631_g1 (annexin D1), c65620_g1 (alpha-amylase isozyme 3C), c61970_g1 (calcium-binding protein KIC), c51736_g1 (ABA), c58408_g1 (DREB3), c66599_g1 (DREB3), c67548_g2 (SOD), c55044_g1 (CAT), c71938_g2 (CAT) and c11358_g1 (GPX) first increased significantly and then decreased significantly with the extension of stress time. Conclusions: A large number of DEGs were identified in P. koraiensis under cold stress, especially the DEGs involved in the perception and transmission of cold signals, the DEGs encoding TFs related to cold regulation and the DEGs removing ROS in antioxidation mechanisms. The transcriptome and digital expression profiling of P. koraiensis could facilitate the understanding of the molecular control mechanism related to cold responses and provide the basis for the molecular breeding of conifers.

This study, conducted in China in November 2020, was aimed at exploring the variations in growth traits among different provenances and families as well as to select elite materials of Juglans mandshurica. Thus, seeds of 44 families from six J. mandshurica provenances in Heilongjiang and Jilin provinces were sown in the nursery and then transplanted out in the field. At the age of 5 years, seven growth traits were assessed, and a comprehensive analysis was conducted as well as selection of provenance and families. Analysis of variance revealed statistically significant (P < 0.01) differences in seven growth traits among different provenances and families, thereby justifying the pursuit of further breeding endeavors. The genetic coefficient of variation (GCV) for all traits ranged from 5.44% (branch angle) to 21.95% (tree height) whereas the phenotypic coefficient of variation (PCV) ranged from 13.74% (tapering) to 38.50% (branch number per node), indicating considerable variability across the traits. Further, all the studied traits except stem straightness degree, branch angle and branch number per node, showed high heritability (Tree height, ground diameter, mean crown width and tapering, over 0.7±0.073), indicating that the variation in these traits is primarily driven by genetic factors. Correlation analysis revealed a strong positive correlation (r > 0.8) between tree height and ground diameter (r = 0.86), tree height and mean crown width (r = 0.82), and ground diameter and mean crown width (r = 0.83). This suggests that these relationships can be employed for more precise predictions of the growth and morphological characteristics of trees, as well as the selection of superior materials. There was a strong correlation between temperature factors and growth traits. Based on the comprehensive scores in this study, Sanchazi was selected as elite provenance. Using the top-percentile selection criteria, SC1, SC8, DJC15, and DQ18 were selected as elite families. These selected families exhibit genetic gains of over 10% in tree height, ground diameter and mean crown width, signifying their significant potential in forestry for enhancing timber production and reducing production cycles, thereby contributing to sustainable forest management. In this study, the growth traits of J. mandshurica were found to exhibit stable variation, and there were correlations between these traits. The selected elite provenance and families of J. mandshurica showed faster growth, which is advantageous for the subsequent breeding and promotion of improved J. mandshurica varieties.

Pinus koraiensis is recognized as one of the most valuable timber and economic tree species. Fruiting properties and growth traits are important characteristics for P. koraiensis breeding, and the relationship between fruiting properties of parents and growth traits of progeny is needed for better understanding. In this study, 71 parental clones and open-pollinated progeny families from the same plus trees were used as materials, and four fruiting properties (cone number per single tree, seed number per single cone, thousand-seed weight, and fruiting individual percentage) and four growth traits (height, diameter at breast height, volume, and survival individual percentage) were measured and calculated. There were significant variations in fruiting properties and growth traits among parental clones and progeny families. For fruiting properties, the phenotypic and genotypic coefficients of variation ranged from 16.51% to 175.34% and from 6.75% to 20.26%, respectively, and the repeatability ranged from 0.3430 to 0.9438. For growth traits, the phenotypic and genotypic coefficients of variation ranged from 15.68% to 39.89% and from 3.51% to 25.99%, respectively, and the broad-sense and narrow-sense heritability ranged from 0.7149 to 0.9681 and from 0.3648 to 0.4614, respectively. There were extremely significant positive correlations between cone number per single tree and fruiting individual percentage, as well as between height, diameter at breast height, and volume. Nevertheless, there was no significant correlation between fruiting properties of parental clones and growth traits of progeny families. Based on the integrated results of principal component analysis and the multi-trait comprehensive evaluation method, six clones (HS23, HS95, HS05, HS73, HS67, and HS17) and four families (HS37, HS17, HS60, and HS54) were selected as elite clones and families, respectively, and HS17 was identified as both an elite parental clone and an elite progeny family. The genetic and realistic gains of elite clones for fruiting properties ranged from 1.34% to 17.34% and from 1.50% to 47.22%, respectively, and the genetic and realistic gains of elite families for growth traits ranged from 4.85% to 33.90% and from 6.73% to 35.02%, respectively. The present study provides the foundation for reconstruction and upgrading of P. koraiensis seed orchards, which is helpful for increasing productivity and economic benefits.

Establishing mixed conifer–broadleaf forests enhances soil multi-nutrient cycling (SMC), yet the underlying mechanisms, particularly the role of rhizosphere microbial communities, remain poorly understood. This study investigated how bacterial and fungal communities in the rhizosphere soil of Larix olgensis drive SMC in both pure and mixed plantations with Fraxinus mandshurica, elucidating the microbial pathways for nutrient supply in mixed stands. Our results indicated that SMC in the L. olgensis rhizosphere soil was significantly greater in mixed stands (0.43) than in pure stands (−0.51). Tree species mixing significantly enhanced microbial diversity, increased the stochasticity of community assembly, and reduced dispersal limitation. Cross-kingdom (bacteria–fungi) co-occurrence networks in mixed stands showed a 19.7% increase in positive correlations, indicating stronger microbial cooperation. Random forest analysis identified microbial diversity, network complexity, and bacterial assembly processes as the main predictors of SMC. Structural equation modeling indicated that microbial diversity indirectly promoted SMC via increased network complexity, while bacterial assembly processes directly influenced SMC. These findings demonstrate that mixed conifer–broadleaf plantations improve soil microbial functioning and nutrient cycling by modifying microbial diversity, assembly processes, and interaction networks.

Biodiversity maintenance mechanisms have been central to the study of community ecology, and the negative density dependence effect plays an important role in maintaining species diversity in forest communities. However, the strength and direction of the negative density dependence effect may change at different latitudinal gradients, and theory predicts that the negative density dependence effect increases with decreasing latitude. Using three provinces in northeastern China as the study target, we selected forest ecosystems in 15 locations according to the latitude gradient and analyzed the mixing of large- and small-diameter trees and adjacent tree species at different latitudinal gradients by the second-order characteristic function of mark mingling (The species mingling was used as “constructed marks” and we developed a second-order characteristic function of mark mingling useful for comparing spatial species mingling via random assignment of species patterns at specific ecological scales). It was found that the tree species mixed level of the large trees was higher, that of the small trees was lower in the stands at the middle and low latitudes (40, 41, and 43), and the tree species mixed level of the large or small trees was lower in the stands at high latitudes (45 and 46). Also, the level of mixing of large trees with surrounding tree species was significantly different among latitudes within the small scale (0–5 m). More importantly, the peak value of the difference in the second-order characteristic function of mark mingling (Δv(r)) of the stand increased gradually with decreasing latitude. The results indicated that the difference in tree species mixing degree between large and small trees was increasing, and this phenomenon was more obvious at the small scale (0–10 m). In general, we found that the negative density dependence effect in the late successional forest system showed a variation trend with latitude gradient, which showed that with the decrease in latitude, the negative density dependence effect in the stands was increasing. The results showed that in temperate forests, in low-latitude stands (40–43° N), there is significant peak in species mingling differences at small scales (0–10 m). Spatial heterogeneity thinning should be prioritized, and rare tree species should be replanted within a 10 m radius to alleviate intraspecific competition. In contrast, in high-latitude stands (45–46° N), human disturbance should be reduced to maintain the natural community structure. These measures can provide precise management strategies for regional biodiversity conservation. This study revealed the response of the intensity of the negative density dependence effect to changes in latitudinal gradients, and provides new ideas for maintaining and controlling regional species diversity.