The effects of cutting length, cutting diameter, and exogenous hormone pretreatment on rooting were studied in comparative experiments to improve the efficiency of cutting propagation in Norway spruce. The results showed that cutting length, diameter, and the interaction between cutting length and diameter significantly affected rooting efficiency. Higher rooting efficiency was obtained by cuttings of 0.3–0.4 cm diameter and 9–12 cm length. Hormone type significantly affected all measured rooting traits, and moderately higher measurements were observed in the indole butyric acid treatment than those of the control, whereas all measurements in the α-naphthalene acetic acid treatment were significantly lower than those of the control, which may have been an inhibitor of Picea abies in stem cuttings. The cutting size effect on rooting efficiency is discussed and an optimal cutting size is suggested, which provide valuable information for propagating Norway spruce.

Picea species are distributed and planted world-wide due to their great ecological and economic values. It has been reported that Picea species vary widely in growth traits in a given environment, which reflects genetic and phenotypic differences among species. However, key physiological processes underlying tree growth and the influencing factors on them are still unknown. Here, we examined needle structures, needle chemical components, physiological characteristics and growth traits across five Picea species in a common garden in Tianshui, Gansu province in China: Picea glauca, P. mariana, P. likiangensis, P. koraiensis, and P. crassifolia, among which P. glauca and P. mariana were introduced from North America, P. likiangensis was from Lijiang, Yunan province in China, P. koraiensis was from Yichun, Heilongjiang province in China, and P. crassifolia was native to the experimental site. It was found that nearly all traits varied significantly among species. Tissue-level anatomical characteristics and leaf mass per area (LMA) were affected by needle size, but the variations of them were not associated with the variations in photosynthetic and biochemical capacity among species. Variations in area-based maximum photosynthesis (P_nmax) were affected by stomatal conductance (g_s), mesophyll conductance (g_m) and biochemical parameters including maximum carboxylation rate (V_cmax), and maximum electron transport rate (J_max). The fraction of N allocated to different photosynthetic apparatus displayed contrasting values among species, which contributed to the species variations in photosynthetic nitrogen use efficiency (PNUE) and P_nmax. Additionally, all growth traits were positively correlated with P_nmax and PNUE. Needle structures are less important than needle biochemical parameters in determining the variations in photosynthetic capacity across the five Picea species. P_nmax and PNUE are closedly associated with the fraction of N allocated to photosynthetic apparatus (P_photo) compared with leaf N content per area (N_area). The tremendous growth differences among the five Picea species were substantially related to the interspecies variation in P_nmax and PNUE.

Conifers are the largest and most ubiquitous group of gymnosperms and have significant ecological significance and economic importance. However, the huge and complex genomes have hindered the sequencing and mining of conifer genomes. In this study, we identified 413 423 transposable elements (TEs) from Picea abies, Picea glauca and Pinus taeda using a combination of multiple approaches and classified them into 11 133 families. A comprehensive web-based database, ConTEdb, was constructed and served for researchers. ConTEdb enables users to browse, retrieve and download the TE sequences from the database. Several analysis tools are integrated into ConTEdb to help users mine the TE data easily and effectively. In summary, ConTEdb provides a platform to study TE biology and functional genomics in conifers.

Monochromatic red light (R) supplementation is more efficient than blue light (B) in promoting Norway spruce (Picea abies (L.) H. Karst) growth. Transcriptome analysis has revealed that R and B may regulate stem growth by regulating phytohormones and secondary metabolites; however, the effects of light qualities on physiological responses and related gene expression in Norway spruce require further study. In the present study, three-year-old Norway spruce seedlings received sunlight during the daytime were exposed to monochromatic B (460 mm), monochromatic R (660 nm), monochromatic far-red light (FR, 730 nm), and a combination of three monochromatic lights (control, R:FR:B = 7:1:1) using light-emitting diode (LED) lamps for 12 h after sunset for 90 day. Growth traits, physiological responses, and related gene expression were determined. The results showed that light quality significantly affected Norway spruce growth. The stem height, root collar diameter, and current-year shoot length of seedlings treated with R were 2%, 10% and 12% higher, respectively, than those of the control, whereas seedlings treated with B and FR showed significantly lower values of these parameters compared with that of the control. The net photosynthetic rate (Pn) of seedlings under R treatment was 10% higher than that of the control, whereas the Pn values of seedlings treated with FR and B were 22% and 33%, respectively, lower than that of the control. The ratio of phosphoenolpyruvate carboxylase to ribulose-1,5-bisphosphate carboxylase/oxygenase (PEPC/Rubisco) of seedlings after the R treatment (0.581) was the highest and 3.98 times higher than that of the seedlings treated with B. Light quality significantly affected the gibberellic acid (GAs) levels, which was 13% higher in seedlings treated with R (6.4 g/100 ng) than that of the control, whereas, the GAs level of seedlings treated with B and FR was 17% and 19% lower, respectively, than that of the control. In addition, seedlings treated with R achieved the lowest ratio of leaf chlorophyll content to fresh weight (8.7). Compared to the R and control treatments, seedlings received FR treatment had consistently lower values of the quantum yield of electron transport beyond Q_A⁻ (primary quinone, ϕEo) and efficiency, with which a trapped exciton moves an electron into the electron transport chain beyond Q_A⁻ (ψo), while higher values of the relatively variable fluorescence at the J step and normalized relatively variable fluorescence at the K step (W_k). The values of ϕEo, ψO, V_J and W_k in seedlings treated with B were similar to those in the control group. The expression of genes associated with light signal transduction, such as PHYTOCHROME C (PHYC), ELONGATED HYPOCOTYL5 (HY5), CONSTITUTIVE PHOTOMORPHOGENIC 1-2 (COP1-2), and PHYTOCHROMEINTERACTING FACTOR 3 (PIF3), was significantly higher in seedlings under B treatment than those under other light treatments. Nevertheless, significant differences were not observed in the expression of COP1-2, HY5, and PIF3 between the R treatment and the control. The expression value of COP1-2 was significantly lower in R than FR light treatments. In conclusion, compared with the control, R promotes, whereas B and FR inhibit Norway spruce growth, which was accompanied by physiological changes and genes expression regulation that may be relate to a changing phytochrome photostationary state (PSS) with the supplemental R in seedlings.