Increased demand for forest-derived biomass has led to more intensive harvesting practices. However, the export of large nutrient quantities with the harvested biomass may lead to the depletion of soil nutrients. Therefore, improved knowledge concerning macronutrient allocation (N, P, K, Ca, and Mg) to different components in forests along age sequences is crucial for their sustainable management. In this study, we quantified nutrient allocation to different ecosystem components, including trees, understorey, forest floor, and different soil depths within a chronosequence (6-, 15-, 23-, and 35-year-old) of larch plantations in China. We then assessed the danger of significant nutrient losses from whole tree harvesting (WTH). Nutrient amounts in trees increased with stand age due to an increase in biomass. Stems accounted for 59%–72% of tree biomass and contained 40%–50% of total tree nutrients in the 15- to 35-year-old stands. The forest floor’s nutrient quantities increased from the 6- to 23-year-old stands and then decreased in the 35-year-old plantations. Conversely, most soil indicators initially declined from 15- to 23-year-old stands and then increased in the 35-year-old stand. The total nutrient stocks were greatest in the soil (0–40 cm), which accounted for about 93%–99% of total nutrients in the larch ecosystem. These data indicate that WTH causes nutrient losses about 2.0–2.5 times higher than stem-only harvesting, when thinning 15- or clear-cut harvesting 23- and 35-year-old stands. However, nutrient losses by WTH have little effect on the soil nutrient pools. Prolonging the crop cycle of larch plantations may be beneficial to improve nutrient return through litterfall and allow available soil nutrients to recover.

A comprehension of the effects planting density and nitrogen (N) fertilization have on the physiological and morphological characteristics of trees is critical for optimizing the require size and characteristics of wood products. We evaluated the growth traits and the leaf and wood characteristics of three clone poplars including Populus simonii × P. nigra ‘Xiaohei’, ‘Xiaohei-14’ and ‘Bailin-3’ under five planting densities (1666, 1111, 833, 666, and 555 tree ha−1) and four N fertilization rates (0, 100, 160, and 220 g tree−1 year−1). The results show that the clone type significantly affected all observed indicators, while planting density and N fertilization treatments had a significant effect on growth traits and leaf characteristics, but not on wood characteristics. Specifically, the clone ‘Bailin-3’ exhibited the largest annual increments in tree height and diameter at breast height (DBH), leaf width, N content, and soluble protein content. A decrease in initial planting density (from 1666 to 555 tree ha−1) led to an increased annual incremental tree height and DBH, regardless of clone type and N fertilization treatment. N fertilization treatment significantly impacted the annual increment in DBH, but not that of tree height. Further, the annual increments in tree height and DBH were positively correlated with leaf width, N content, chlorophyll content, and soluble protein content, and negatively correlated with hemicellulose content. In addition, the chlorophyll and soluble protein contents were identified as the most reliable predictors of the annual increments in tree height and DBH. Our results demonstrate the clone ‘Bailin-3’ with 555 tree ha−1 under 160 g N tree−1 yr−1 showed superior growth traits and leaf characteristics. Thus, it is recommended for future poplar silviculture of larger diameter timber production at similar sites. The results contribute to understanding of the effects of planting density and fertilization on the growth traits and the leaf and wood characteristics of three poplar clones, offering valuable guidance for the sustainable development and long-term productivity of poplar plantations.

The aim of this paper was to investigate the transcriptomic and metabolomic differences in Populus cathayana × canadasis ‘Xinlin1’ (P. cathayana × canadasis ‘Xinlin 1’) under varying irrigation and fertilization conditions. Ten-year-old P. cathayana × canadasis ‘Xinlin 1’ was selected as the test subject in this study; different irrigation and fertilization treatments were set up, and DEGs and DAMs in response to water and fertilizer regulation were identified. Transcriptomic and metabolomic profiles were analyzed from both leaves and roots. A total of 22,870 DEGs were identified in response to water and fertilizer treatments, predominantly belonging to 48 transcription factor families, including MYB, ERF, and MYB-related ones. Additionally, 2432 DAMs were detected and categorized into 18 metabolite classes, with flavonoids being the most abundant (342 metabolites), followed by terpenoids, lipids, and others. KEGG enrichment analysis revealed that DEGs and DAMs were significantly associated with pathways such as plant hormone signal transduction and starch and sucrose metabolism pathways. The levels of ABA exhibited an initial decrease followed by an increase, with several key genes, including PYR/PYL, PP2C, SnRK2, and ABF, also differentially expressed in the plant hormone signal transduction pathway. In the starch and sucrose metabolic pathways, sucrose was more hydrolyzed into D-fructose, which gradually translocated from roots to leaves. DEGs were significantly involved in sucrose synthesis and decomposition into D-fructose and 1,3-β-glucose, as well as starch synthesis and starch decomposition into cellulose dextrin, which underwent complete hydrolysis to glucose. In the starch hydrolysis process, 29 DEGs were involved, with 12 down-regulated and 17 up-regulated.