In light of the detrimental effects of global warming, exacerbated by the intense sunlight and high temperatures prevalent during summer in southern China, on the growth of Melaleuca alternifolia (M. alternifolia) seedlings, this study sets out to examine the impact of various shading treatments on the growth and physiological attributes of M. alternifolia seedlings, with the aim of determining the optimum shading level. The seedling phase is of paramount importance in the growth cycle and regeneration process of M. alternifolia, as both excessive and insufficient light exposure can negatively influence seedling development. Four shading regimes (CK: no shading; C1: 35–45% shading; C2: 45–50% shading; C3: 60–70% shading) were imposed on M. alternifolia seedlings, following which observations were conducted after a 35-day period. The results reveal that the different shading treatments had a significant effect on the growth and physiological indicators of the seedlings, with the moderate shading treatment (C2) proving to be the most advantageous for seedling growth. Under the C2 treatment, an increase in chlorophyll content was observed in the leaves of the seedlings, accompanied by a decrease in malondialdehyde (MDA) content. Concurrently, there was a reduction in the activities of antioxidant enzymes, namely superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). Furthermore, the levels of abscisic acid (ABA) and gibberellic acid (GA3) declined, while the concentrations of auxin (IAA), salicylic acid (SA), and cytokinin (CTK) ascended. Leaf anatomical analysis disclosed that, in comparison to the control group, the thickness of the lower epidermis and palisade tissue in the leaves of the seedlings subjected to the C2 treatment exhibited a significant reduction. Additionally, an increase in the number of spongy tissue cells was noted, along with a marked increase in total leaf thickness. Consequently, cultivating M. alternifolia seedlings under shading conditions ranging from 45 to 50% is deemed more favorable. The findings of this study offer novel insights into the adaptive responses of M. alternifolia seedlings to varying light intensities and provide theoretical guidance for the cultivation and management of M. alternifolia seedlings in the southern regions of China.

Rapid growth and scattered plant types are urgent issues for potted Melaleuca alternifolia. An effective strategy for dwarfing cultivation is the exogenous application of plant growth regulators (PGRs) to plants. However, for many non-wood forest species, there is currently limited understanding of the regulatory mechanism of dwarfing effects of PGRs, which greatly limits the application of PGRs. In this study, three PGRs, paclobutrazol (PP333), uniconazole (S3307), and chlormequat chloride (CCC) were applied to dwarf terpinen-4-ol M. alternifolia. By observing the morphological characteristics and leaf anatomy of M. alternifolia after dwarfing and measuring its photosynthetic characteristics and physiological and biochemical indexes, the dwarfing effect of the three PGRs and the underlying mechanisms were investigated to provide a reference for the cultivation of M. alternifolia by dwarfing. The results show that the PP333 (P3) treatment at 2000 mg·L⁻¹ had the best dwarfing effect on M. alternifolia, with a compact plant shape, thicker stems, and green leaf color. At the same time, it increased the chlorophyll contents, changed the blade structure, increased the content of soluble substances and the activity of antioxidant enzymes, increased the endogenous hormones indole-3-acetic acid (IAA), gibberellin A3 (GA3), and trans-zeatin-riboside (ZR), and decreased abscisic acid (ABA) levels.

Long-term unreasonable management has led to the continuous decline of soil quality in Melaleuca alternifolia planting areas in southern China, and there is no effective way to improve its soil quality at present. In this study, residues of tea tree oil extraction were returned to the forest to explore its influence on soil quality. Therefore, four test groups (RT, residues were tiled; RS, residues were stacked; RDT, residues were decomposed and tiled; RDS, residues were decomposed and stacked) and one control group (CK, nothing was changed) were designed. We used one-way ANOVA and Pearson correlation analysis to detect 22 physical, chemical, and biological indicators of soil, and then used minimum data set (MDS) and principal component analysis (PCA) to evaluate soil quality. The results show that compared with the CK, BD and pH in the test groups decreases, while CP, TTP, SOM, AN, NN, AP, AK, CEC, MBC, MBN, MBP, catalase, urease, sucrase, and ACP increase or strengthen in different degrees, and the biomass increases by 5.3%~12.8%. The soil quality indexes (SQI) are RDT (0.616) > RT (0.546) > RDS (0.525) > RS (0.452) > CK (0.291). Significant correlation between SQI and biomass indicates that the indicators have high biological significance for the planting areas of Melaleuca alternifolia in the red soil region in southern China. These results show that residues could improve soil quality, and that the soil quality is different among different test groups. This study provides a new path for the management of Melaleuca alternifolia plantation.

The carbon sink capacity of forest ecosystem and its function of mitigating climate change have been confirmed. As two common coniferous species, Cunninghamia lanceolata (Lamb.) Hook. (C. lanceolata) and Pinus elliottii Engelmann (P. elliottii) are widely planted in southern China, and their carbon sink capacity has always been concerning. According to their diameter class, we randomly harvested 42 C. lanceolata trees and 38 P. elliottii trees from our entire study area, measured their carbon concentration, and constructed biomass models with DBH and tree height as variables. The biomass of the tree layer was estimated by measuring the DBH of all trees in the plots, and the biomass and carbon concentration of shrubs, herbs, dead wood and litter in the plot were measured by harvesting them. The results showed that the total biomass in C. lanceolata and P. elliottii plantations were 117.1 and 151.8 t·ha⁻¹; the biomass in the tree layer was 94.7 and 122.9 t·ha⁻¹; and in the other parts was 22.4 and 28.9 t·ha⁻¹, respectively. In addition, the total carbon densities in the C. lanceolata and P. elliottii plantation ecosystems were 166.3 and 198.6 t·ha⁻¹; the carbon densities in the soil were 108.1 and 124.6 t·ha⁻¹; and in the other parts, they were 58.2 and 74.0 t·ha⁻¹, respectively. These results indicate that there are significant differences in total biomass or total carbon storage between the two coniferous forest ecosystems, and net productivity and carbon sink capacity are higher in the P. elliottii plantation ecosystem. This study lays the foundation for the biomass estimation and carbon trading of these two coniferous forests in northern Hunan.

This study investigated whether plantation productivity increases with planting density, using Pinus massoniana plantations in subtropical China as a case study. Three afforestation densities were established: low (A: 1667 trees·hm-2), medium (B: 2500 trees·hm-2), and high (C: 3333 trees·hm-2). Sixteen permanent sample plots (8-32 yr) were monitored in 2023 and 2025. Individual size differentiation (Gini coefficient), diameter-class distribution, stand volume, biomass, net primary productivity (NPP), and biomass energy productivity (BEP) were analyzed. The results showed that the Gini coefficient increased significantly with planting density (mean values: 0.233, 0.282, 0.311 for A, B, C; p<0.05), and decreased with stand age (linear R2=0.894-0.931). Low-density stands produced large-diameter timber earlier (14 yr) and had higher proportions of large-medium timber (90.2% by age 30) than high-density stands (small-diameter still 21.1%). Stand volume peaked around age 20, then slowed. Volume productivity was highest in low density (mean 17.91 m3·hm-2·yr-1) and decreased with density (C: 9.42). NPP and BEP followed the same pattern: low density had significantly higher NPP (7.83 vs. 5.66 t·hm-2·yr-1) and BEP (170.27 vs. 123.54×106 kJ·hm-2·yr-1) than high density. The structural equation model revealed that afforestation density positively affected Gini and number of living trees, while stand age negatively affected volume productivity. Moderate differentiation (Gini) positively influenced NPP (0.517). We conclude that lower initial planting density (≈1667 trees·hm-2) is more beneficial for long-term productivity, timber quality, and biomass energy accumulation. Increasing density does not increase overall productivity and should be avoided in sustainable plantation management