Mineral accumulation in plants under drought stress is essential for drought tolerance. The distribution, survival, and growth of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.), an evergreen conifer, can be affected by climate change, particularly seasonal precipitation and drought. Hence, we designed a drought pot experiment, using 1-year-old Chinese fir plantlets, to evaluate drought effects under simulated mild drought, moderate drought, and severe drought, which corresponds to 60%, 50%, and 40% of soil field maximum moisture capacity, respectively. A treatment of 80% of soil field maximum moisture capacity was used as control. Effects of drought stress on mineral uptake, accumulation, and distribution in Chinese fir organs were determined under different drought stress regimes for 0–45 days. Severe drought stress significantly increased phosphorous (P) and potassium (K) uptake at 15, 30 and 45 days, respectively, within fine (diameter < 2 mm), moderate (diameter 2–5 mm), and large (diameter 5–10 mm) roots. Drought stress decreased magnesium (Mg) and manganese (Mn) uptake by fine roots and increased iron (Fe) uptake in fine and moderate roots but decreased Fe uptake in large roots. Severe drought stress increased P, K, calcium (Ca), Fe, sodium (Na), and aluminum (Al) accumulation in leaves after 45 days and increased Mg and Mn accumulation after 15 days. In stems, severe drought stress increased P, K, Ca, Fe, and Al in the phloem, and P, K, Mg, Na, and Al in the xylem. In branches, P, K, Ca, Fe, and Al concentrations increased in the phloem, and P, Mg, and Mn concentrations increased in the xylem under severe drought stress. Taken together, plants develop strategies to alleviate the adverse effects of drought stress, such as promoting the accumulation of P and K in most organs, regulating minerals concentration in the phloem and xylem, to prevent the occurrence of xylem embolism. The important roles of minerals in response to drought stress should be further evaluated.

The Chinese fir Cunninghamia lanceolata (Lamb.) Hook. is an important timber conifer species in China. Much has been studied about Chinese fir, but the distribution of non-structural carbohydrates (NSCs) among different organs (needles, branch, stem, and roots) under drought stress remains poorly understood. In this study, we used one-year-old C. lanceolata plantlets to evaluate the effects of simulated drought under four water regimes, i.e., adequate water or control, light drought, moderate drought, and severe drought stress corresponding to 80%, 60%, 50%, and 40%, respectively of soil field maximum capacity on various NSCs in the needles, branch, stem and roots. The degree and duration of drought stress had significant effects on fructose, glucose, sucrose, soluble sugar, starch, and NSC content in various organs (p < 0.05). Fructose content increased in stem xylem, stem phloem, and leaves. Glucose and sucrose content declined in stem and branch xylem under light drought stress and moderate drought stress, and increased under severe drought stress conditions. Soluble sugars content declined, and starch content increased in leaf and branch phloem, but the latter could not compensate for soluble sugar consumption in the whole plant, and therefore, total NSCs decreased. Correlation analysis showed that a significant positive correlation existed in the soluble sugar content between leaves and roots, and between xylem and phloem in the stems and branches. Chinese fir appears to have different NSCs distribution strategies in response to drought stress, viz., allocating more soluble sugars to fine roots and increasing starch content in the needles, as well as ensuring osmosis to prevent xylem embolism. Our study may broaden the understanding of the various mechanisms that Chinese fir and other plants have to enhance their tolerance to drought stress.

Heat shock transcription factors (HSFs) activate heat shock protein gene expression by binding their promoters in response to heat stress and are considered to be pivotal transcription factors in plants. Eucalyptus is a superior source of fuel and commercial wood. During its growth, high temperature or other abiotic stresses could impact its defense capability and growth. Hsf genes have been cloned and sequenced in many plants, but rarely in Eucalyptus. In this study, we used bioinformatics methods to analyze and identify Eucalyptus Hsf genes, their chromosomal localization and structure. The phylogenetic relationship and conserved domains of their encoded proteins were further analyzed. A total of 36 Hsf genes were identified and authenticated from Eucalyptus, which were scattered across 11 chromosomes. They could be classified into three classes (A, B and C). Additionally, a large number of stress-related cis-regulatory elements were identified in the upstream promoter sequence of HSF, and cis-acting element analysis indicated that the expression of EgHsf may be regulated by plant growth and development, metabolism, hormones and stress responses. The expression profiles of five representative Hsf genes, EgHsf4, EgHsf9, EgHsf13, EgHsf24 and EgHsf32, under salt and temperature stresses were examined by qRT-PCR. The results show that the expression pattern of class B genes (EgHsf4, EgHsf24 and EgHsf32) was more tolerant to abiotic stresses than that of class A genes (EgHsf9 and EgHsf13). However, the expressions of all tested Hsf genes in six tissues were at different levels. Finally, we investigated the network of interplay between genes, and the results suggest that there may be synergistic effects between different Hsf genes in response to abiotic stresses. We conclude that the Hsf gene family played an important role in the growth and developmental processes of Eucalyptus and could be vital for maintaining cell homeostasis against external stresses. This study provides basic information on the members of the Hsf gene family in Eucalyptus and lays the foundation for the functional identification of related genes and the further investigation of their biological functions in plant stress regulation.

To guide the cultivation of superior Chinese fir plantlets, we designed an L₁₆(4)⁴ orthogonal experiment to determine how leaf age and exogenous hormones influence key growth processes in leaf cuttings. Hormone concentration and treatment duration significantly affected leaf cuttings in all three age categories; 6-benzylaminopurine (6-BA), 1-naphthaleneacetic acid (NAA), and treatment time exerted the strongest effects on callus initiation rates. Additionally, NAA had the largest effect on the rooting rate across all cuttings, and all three hormones significantly influenced the bud germination rate. Based on our experimental results, expected optimal treatments for callus initiation were 10 mg∙L⁻¹ indole-3-butyric acid (IBA) for 10 min, 30 mg∙L⁻¹ NAA for 15 min, and 10 mg∙L⁻¹ NAA plus 30 mg∙L⁻¹ IBA for 10 min. For the rooting rate, the expected optimal treatment was 50 mg∙L⁻¹ NAA and 40 mg∙L⁻¹ IBA for 5–20 min. Finally, for bud germination, optimal treatments were 20 min of immersion in water, 30 mg∙L⁻¹ 6-BA plus 50 mg∙L⁻¹ NAA for 15 min, and 30 mg∙L⁻¹ 6-BA for 5 min. Plantlet formation only occurred in the <one-year-old leaves, and at very low rates (maximum 5.8%); this outcome is likely attributable to the mother plant’s relatively old age (five years). Plantlet formation from cuttings is dependent on ensuring the rooting rate after callus initiation. Therefore, to promote rooting rates and bud germination, we recommend leaving more xylem at the base of leaf cuttings.

The prolonged retention of senescent branches and needles (canopy litter) in Cunninghamia lanceolata canopies is an evolutionary adaptation, yet its impacts on stand microenvironment and understory succession remain poorly quantified. To address this gap, we conducted a 5-year field experiment across six planting densities (1800, 2400, 3000, 3600, 4200, and 4800 trees·ha⁻¹), aiming to evaluate the effects of canopy litter removal on canopy structure, forest light environment, and understory biodiversity. Results demonstrated that leaf area index (LAI) and mean tilt angle of the leaf (MTA) significantly increased with density (p < 0.05), leading to marked reductions in photosynthetic photon flux density (PPFD) and light transmittance (T). Canopy litter removal significantly reduced LAI across all densities after 4–5 years (p < 0.05) and consistently enhanced PPFD and transmittance (p < 0.01). MTA and light quality parameters (red:blue and red:far-red ratios) both exhibited variable responses to litter removal, driven by density and time interactions, with effects diminishing over time. Understory vegetation diversity exhibited pronounced temporal dynamics and density-dependent responses to canopy litter removal, with increases in species richness (S), Simpson diversity (D), and Shannon–Wiener diversity (H), while Pielou Evenness (J) responded more variably. The most notable increase in species richness occurred in the 4th year, when 21 new species were recorded, largely due to the expansion of light-demanding bamboos (e.g., Indocalamus tessellatus and Pleioblastus amarus), heliophilic grasses (e.g., Lophatherum gracile) and pioneer ferns (e.g., Pteris dispar and Microlepia hancei). Correlation analyses confirmed PPFD as a key positive driver of all diversity indices (p < 0.01), whereas LAI was significantly negatively correlated with PPFD, light transmittance, and understory diversity (p < 0.01). These findings demonstrate that strategic management of canopy litter incorporating stand density regulation can improve understory light availability, thereby facilitating heliophilic species recruitment and biodiversity enhancement in subtropical coniferous plantations.

Marcescence (the retention of dead leaves) is a widespread trait in many tree species, yet its ecological functions and adaptive significance remain poorly understood. This study examined how four light regimes (open, edge, gap, and interior forests) affect light distribution, marcescent biomass, and upper-canopy photosynthesis in Cunninghamia lanceolata, a dominant subtropical timber species in China. We further elucidated its light-optimization mechanisms under low-light conditions. Results revealed that photosynthetic photon flux density (PPFD), irradiance, and transmittance declined from open to interior forests at equivalent canopy heights, while particularly steep declines in PPFD from canopy top to bottom occurred in interior stands (P < 0.05). Marcescent biomass was significantly higher in interior forest (3801 g·tree^-1) and lowest in open stands (1265 g·tree^-1), with intermediate masses in edge and gap forest. Two-way ANOVA confirmed light regime and canopy height as dominant factors controlling marcescent biomass, with canopy shading promoting upward accumulation in interior forests (P < 0.05). Upper-canopy needles in interior forests showed decreased maximum net photosynthetic rate (P_max), light saturation point (LSP), light compensation point (LCP), and dark respiration rate (R_d), but increased light use efficiency (LUE). Lower-canopy marcescent biomass (total, needle, and branch) was significantly negatively correlated with P_max, LSP, LCP and R_d, but significantly positively correlated with leaf-level LUE in the upper canopy (P < 0.05), indicating that light limitation-induced marcescence enhances photon use efficiency in upper-canopy needles. These findings highlight an evolutionary growth-survival trade-off strategy in which Chinese fir sacrifices lower-canopy growth to optimize upper-canopy carbon gain under light scarcity, favoring long-term biomass accumulation over short-term growth. By clarifying the functional role of marcescence in low-light adaptation, our study provides globally relevant insights for management of marcescent tree species across different biomes, including density regulation, canopy light optimization, and targeted pruning protocols that leverage retained marcescent biomass for resource allocation efficiency.