Poplars are crucial for timber supply and ecological protection in China. Enhancing the growth of poplar plantations and improving soil fertility in arid, and semi-arid poor soil regions are key aspects of sustainable forest management. Fertilization (FTL) and drip irrigation (DI) are among the most widely used methods globally for increasing yield and soil productivity. This study conducted field experiments on FTL and DI in a 10-year-old Populus × canadensis ‘Zhongliao 1’ (cultivation varieties of P. canadensis in northern China) plantation. DI limits were set according to soil moisture at 60% (S1), 70% (S2), and 80% (S3) of field capacity; nitrogen FTL rates were set at 100% of the baseline fertilization amount (100% BFA, N 643.20 g·year⁻¹, P 473.37 g·year⁻¹, and K 492.29 g·year⁻¹) (F1), 70% BFA (F2), 130% BFA (F3), and 160% BFA (F4). The treatments of drip irrigation and fertigation (DIF) were H1 (100% BFA, 60% FC), H2 (100% BFA, 80% FC), H3 (160% BFA, 60% FC), and H4 (160% BFA, 80% FC), along with a control group (CK) without any management, totaling 12 experimental combinations. The results showed that the H4 had the most significant promoting effect on the height, DBH, and volume increments. All treatments had little effect on the soil bulk density of the plantation but significantly impacted soil capillary porosity and pH. Compared to DI, soil nutrient and organic matter content were more sensitive to FTL. Appropriate FTL and DI can increase soil sucrase activity. Soil urease activity tended to increase with higher FTL rates, and higher DI levels also positively influenced urease activity. Excessive or insufficient soil moisture and nutrients negatively impacted soil cellulase and catalase activities. Correlation analysis revealed no significant correlation between the growth of P. × canadensis ‘Zhongliao 1’ and soil nutrient content, but significant or highly significant correlations existed between growth and soil porosity and related enzyme activities. Comprehensive evaluation using a membership function indicated that high FTL levels (F4) were more conducive to the simultaneous improvement of the growth and soil fertility of the plantation, followed by H4 and F1, suggesting that high FTL is the key factor affecting the growth of 10-year-old P. × canadensis ‘Zhongliao 1’ plantations and the restoration of stand productivity, with moisture being secondary.

Poplar is an important tree species for timber supply and ecological protection in northern China. Cultivating and selecting high-quality varieties and germplasm resources suitable for cultivation are key factors in enhancing the quality and productivity of poplar plantations in the arid and semi-arid northern regions with shorter growing seasons. This study conducted a field cultivation experiment on 10 progeny clones from the direct cross (D × M) of imported Populus deltoides ‘DD-109’ with Populus maximowiczii and 7 progeny clones from the reciprocal cross (M × D) using one-year-old rooted cuttings planted at a 4 m × 8 m spacing. Based on 17 years of annual growth observations, the study systematically compared growth characteristics, age of quantitative maturity, path relationships between traits, and early selection efficiency in the hybrid offspring. The results indicated that the D × M population had superior diameter at breast height (DBH), tree height (H), and volume (V) compared to the M × D population, while the height-to-diameter ratio (HDR) was lower. The growth rate of the 17 clones peaked from 10 to 14 years, with annual volume growth increments (PAIs) higher than mean annual volume increments (MAIs) during the early growth stages; the quantitative maturity age ranged between 12 and 16 years. The D × M population generally reached quantitative maturity earlier than the M × D population, with the fastest clone maturing in 12 years. Four clones (DM-9-17, DM-9-18, DM-9-14, and MD-61) showed values for V, DBH, H, and HDR above the hybrid group average. Path analysis demonstrated that DBH had the most significant direct and indirect effects on V, suggesting it as the best predictor for V. Using DBH as a reference, correlation and early selection efficiency analysis showed a strong relationship between growth characteristics at planting years 4–5 and later-stage performance, indicating this as the optimal period for early selection. These findings contribute to evaluating the production potential of P. deltoides ‘DD-109’ and P. maximowiczii germplasm in northern China and provide valuable guidance for selecting poplar clones suitable for local cultivation, accelerating breeding processes, and informing management planning for poplar plantations.

The classification and identification of species in Populus has remained a formidable challenge due to widespread interspecies hybridization. The complete chloroplast genome of Populus maximowiczii was obtained by Illumina high-throughput sequencing technology, with a typical quadripartite structure and 37.0% GC content. The chloroplast genome of P. maximowiczii was 156,892 in length, including a large single-copy region (LSC: 84,988 bp), a small single-copy region (SSC: 16,630 bp), and a pair of inverted repeats (IRs: each 27,637 bp in length). A total of 131 genes were annotated, including 86 protein-coding genes, 37 tRNAs, and 8 rRNAs. The phylogenetic analysis indicated that 43 species belonging to Populus were classified into monophyly, with P. cathayana being the closest relatives to P. maximowiczii. In conclusion, this study provides valuable insights into understanding the phylogeny of Populus.

Monoculture plantations often face challenges of soil degradation and declining ecosystem services. Intercropping is beneficial to improving soil quality; however, the long-term effects of intercropping woody plants with medicinal herbs on soil ecosystems remain unclear. This study aimed to investigate the temporal effects of different durations of poplar intercropping with Aralia elata on soil physicochemical properties, enzyme activities, and soil microbial community structure. Soil samples were collected from the 0–20 cm soil layer, with composite samples obtained by mixing four soil cores per plot. We determined soil physicochemical properties, including pH, total carbon (TC), total nitrogen (TN), and total phosphorus (TP); soil enzyme activities, including invertase, urease, phosphatase, and β-N-acetylglucosaminidase (NAG); and soil microbial community structure using high-throughput sequencing of the bacterial 16S rRNA gene and fungal ITS region. Intercropping significantly affected soil chemical properties and enzyme activities in poplar plantations. Compared with the monoculture control (Y), TN (p < 0.01) and TC (p < 0.01) contents increased significantly in the 3- and 7-year intercropping treatments. The activity of β-N-acetylglucosaminidase (NAG) was enhanced following poplar–Aralia elata intercropping. In addition, intercropping significantly changed the composition and structure of soil microbial communities. In summary, introducing Aralia elata into poplar plantations can effectively improve soil fertility and reshape soil microbial community structure. This positive effect is time-dependent and becomes more significant with a 7-year intercropping duration. Poplar–Aralia elata intercropping represents a feasible management strategy to enhance ecological sustainability and soil health in plantation ecosystems of Northeast China.