Pinus koraiensis, as a keystone tree species, possesses immense economic and ecological value. However, the present cultivation of high-quality seedlings in Pinus koraiensis plantations remains hindered by prohibitively high costs and inadequate technological advancements. Additionally, the species’ prolonged growth cycle and low yield, when compounded by issues such as excessive harvesting, may result in supply constraints. Plant growth regulators (PGRs), a class of naturally occurring or synthetically derived chemical compounds, are capable of modulating plant development and physiology. These regulators exert notable effects by enhancing root proliferation, facilitating lignification, influencing plant architecture, and augmenting yield. Owing to their operational simplicity and relatively low cost, PGR applications hold substantial promise for cultivating Pinus koraiensis seedlings with superior traits. In this study, four-year-old Pinus koraiensis seedlings were employed to evaluate the impacts of three PGRs (paclobutrazol, chlormequat chloride, and diethyl aminoethyl hexanoate), alongside varied application methods (dosage and frequency), on the growth, physiological, and photosynthetic parameters of the seedlings. The findings revealed that treatment with 1.5 g/L paclobutrazol produced the most pronounced effects across a range of indicators. Specifically, this treatment markedly enhanced growth traits (e.g., branch diameter, new shoot length, lateral branch length, aboveground fresh and dry weights, root fresh and dry weights, lateral root dry weight, and number of second-order roots), physiological attributes (e.g., increased superoxide dismutase and peroxidase activities, elevated lignin content, and reduced relative conductivity and malondialdehyde levels), and photosynthetic metrics (e.g., elevated net photosynthetic rate, stomatal conductance, transpiration rate, and maximum net photosynthetic rate), thereby constituting the optimal treatment combination.

Water is a primary element restricting the growth and survival of trees; thus, drought stress has a negative impact on plant development. In the current study, the transcriptional and metabolic changes in Populus davidiana were investigated under drought stress. We found that the chlorophyll content of poplars decreased, and reactive oxygen species (ROS) accumulation increased during drought stress. Following 2, 4, 6, 8, and 10 d of drought stress, 2127, 5334, 8894, 11,279, and 11,778 differentially expressed genes (DEGs) were identified, according to transcriptome analysis results. Enrichment analysis showed that a large number of DEGs were enriched in photosynthesis, chlorophyll decomposition and synthesis, and secondary metabolism-related pathways. The results of metabolomics analysis indicate that 131, 378, 334, 365, and 646 metabolites accumulated differentially following 2, 4, 6, 8, and 10 d, respectively, of drought stress. According to K-means clustering analysis, the contents of flavonoids significantly decreased alongside gene expression levels, while lipid content increased at 10 d of drought stress, alongside most of the related gene expression levels. Based on these data, two gene regulatory networks (GRNs) for lipid metabolism and flavonoid synthesis were constructed, each containing 45 transcription factors (TFs). Among them, six TFs (ERF39, GAI, ERF34, DOF5.2, DREB2A, and C3H6) were shared by two GRNs, suggesting that they may have diverse functions in response to drought stress. In summary, this study provides candidate genes for cultivating drought-resistant varieties and offers new insights into enhancing that resistance.

The Short Internodes-Related Sequence (SRS) family is a class of transcription factors unique to plants that are essential for controlling their growth, development, and stress responses. Nevertheless, information regarding the characterization and biological function of poplar SRS family members remains limited. In this study, we identified 10 members of the SRS gene family in the genome of Populus tremula using bioinformatics, distributed on seven chromosomes and named PtSRS01-PtSRS10 based on their locations. Our phylogenetic analysis results indicated that PtSRS genes can be categorized into five subfamilies and that members of each subfamily have similar gene structures and motifs. Collinearity analysis indicated that the expansion of the PtSRS gene family is caused by segmental duplication and is influenced by purifying selection during its evolutionary process. Cis-acting element analysis revealed that PtSRS was enriched in cis-acting elements related to growth and development, light response, hormone induction, and stress response. Quantitative real-time PCR revealed that drought and salt (NaCl) treatments affected the expression of several PtSRS genes, with PtSRS04 and PtSRS05 being the two genes with the most significant expression levels, with PtSRS04 showing a 700-fold increase in relative gene expression level after 8 d of drought stress and the PtSRS05 gene showing a 38-fold increase in gene expression level at 48 h of NaCl stress, suggesting that they could be crucial in salt and drought stress. The results presented herein provide a theoretical basis for subsequent in-depth studies on the involvement of poplar SRS gene family members in drought and salt stress resistance.