Cold temperatures ('chilling') perceived by tree buds progressively release winter dormancy and initiate sensitivity to warmer temperatures ('forcing') required for budburst. Phenology of temperate trees may also respond to daylength, but it remains unclear whether chilling and forcing accumulation is linked to the diurnal cycle. Here, we tested whether chilling accumulation is influenced by light-dark cycle frequency, and whether forcing is more effective during daylight. We harvested twig cuttings from four temperate tree species (Fagus sylvatica, Carpinus betulus, Quercus robur and Acer pseudoplatanus) with contrasting chilling and forcing requirements. In Experiment 1, twigs were harvested in November and exposed to 3°C under three light-dark cycle frequencies: 12h light/12h dark, 6h/6h, and 4h/4h (1, 2 or 3 cycles/day) for one or two months (short vs. long chilling). Twigs were then transferred to two forcing regimes with the same daily mean but different day/night temperatures (25°C/10°C and 20°C/15°C). In Experiment 2, twigs were harvested after substantial chilling and exposed to opposite day/night forcing regimes (25°C/10°C vs. 10°C/25°C). In Experiment 1, shorter light-dark cycles under long chilling delayed budburst in C. betulus, whereas effects on budburst success depended on chilling duration in C. betulus and Q. robur. Interestingly, budburst occurred significantly earlier at 25°C/10°C than at 20°C/15°C in all species, up to 12 days in F. sylvatica, suggesting more effective daytime forcing or non-linear forcing accumulation. Experiment 2 demonstrated that forcing was more effective during daylight, with 10%, 19% and 51% more degree days required for budburst under warm nights in Q. robur, C. betulus and F. sylvatica, respectively, but no difference in A. pseudoplatanus. Our study shows that light-temperature interactions and non-linear forcing responses can shape budburst timing, implying that tree phenological responses to warming may depend not only on its magnitude but also on its timing within the diurnal cycle.

Cadmium (Cd) contamination threatens soil ecosystems and food security. Robinia pseudoacacia is a potential candidate for phytoremediation, but the molecular responses and root-associated microbial responses accompanying rhizobial symbiosis under Cd exposure remain incompletely understood. We integrated root transcriptomic, internal-root metabolomic, and 16S rRNA gene sequencing data to characterize responses to Cd exposure and rhizobial inoculation in SX, the high shoot-Cd accumulator, and HB, the low shoot-Cd accumulator. SX and HB exhibited distinct transcriptional patterns and exploratory candidate-metabolite profiles. In SX, the transcriptional responses were associated with the greater shoot Cd translocation reported previously for this genotype. In HB, rhizobial inoculation under Cd exposure was associated with broader changes in candidate metal-transport and compartmentalization genes, consistent with its previously reported greater root Cd retention. Rhizobial inoculation was also associated with higher candidate abundances of leucine, trehalose, palmitic acid, thymine, and pantothenates in HB, whereas inoculated SX showed higher candidate abundances of leucine and isoleucine but lower internal L-malic acid. Cd exposure, rhizobial inoculation, and root compartment were associated with variation in bacterial community composition, including abundance patterns involving Pseudomonas, Devosia, and Rhizobium. Exploratory Spearman correlation analyses revealed compartment-specific patterns of covariation between candidate metabolites and bacterial genera; however, no metabolite-genus association remained statistically significant after Benjamini-Hochberg correction in the rhizoplane, endosphere, or rhizosphere. None of the compartment-specific Procrustes tests indicated significant overall concordance between bacterial community composition and root-metabolite profiles. Collectively, these findings identify candidate genes, metabolites, and bacterial taxa and provide testable hypotheses that could inform future genotype selection and microbiome-assisted phytoremediation strategies.

To investigate N physiology and metabolism of different Catalpa bungei (C. bungei) genotypes in response to low N availability, saplings of a genotype (Cbu22-03) with high N uptake efficiency and a genotype (CbuGu) with low N uptake efficiency were exposed to 10, 100, or 1000 μM NH4NO3. The greater root biomass and fine-root surface area in Cbu22-03, combined with its higher net influxes of NO3- and NH4+ and upregulated transcript levels of CbuNRT1.1 and CbuAMT1.2, corresponded to the increased NO3- and NH4+ concentrations and total N amounts in roots compared with CbuGu. Accordingly, δ15N in both roots and leaves of Cbu22-03 was lower than that of CbuGu. Low N supply led to decreased net influxes of NO3- and NH4+, and reduced NO3-/NH4+ concentrations of roots and leaves, NR activities, and total N amounts, while inducing the up-regulation of CbuNRT1.1, CbuAMT1.2, and CbuAHA2 transcript levels, which likely enhanced nitrogen use efficiency (NUE) in both genotypes. These data suggest that Cbu22-03 shows greater capacities of N uptake and assimilation than CbuGu under the three N conditions, and both genotypes of C. bungei decreased the processes of N metabolism in response to low N availability.

Atmospheric nitrogen (N) deposition can substantially alter nutrient balance and internal nutrient recycling in trees, yet how dioecious species regulate phosphorus (P) economy in a sex-specific manner under N enrichment remains poorly understood. We investigated how short-term N enrichment differentially modifies leaf functional traits, leaf stoichiometry, and nitrogen and phosphorus resorption efficiencies (NRE and PRE) in female and male Fraxinus velutina Torr. using a field canopy-spray experiment with two N addition levels. Although N addition consistently promoted leaf structural traits, neither sex nor the N × S interaction significantly affected leaf morphological traits, suggesting that sexual dimorphism in this species manifests primarily in nutrient economy rather than leaf structure. Under N enrichment, P-related traits exhibited pronounced sex-specific responses, with significant N × S interactions: under high N, females increased leaf P concentration and exhibited lower N:P, whereas males increased leaf N concentration, resulting in higher N:P. N addition reduced NRE in both sexes, but PRE responses differed markedly: PRE declined progressively in males under elevated N, while females maintained a moderate reduction in PRE. SMA and multivariate analyses further showed that nutrient resorption in males was more strongly associated with current-season stoichiometric variation, whereas in females, nutrient resorption showed a stronger association with P status. Together, these findings identify P balance as the primary axis of sex-specific nutrient regulation under N enrichment, with females maintaining more stable internal P homeostasis than males. This distinction that underscores the need to account for plant sex in assessments of dioecious tree responses to increasing atmospheric N deposition.

Tilia mandshurica is an important woody nectar plant, but the genomic and transcriptional basis of its nectar sugar accumulation remains poorly understood. Here, we generated a chromosome-level reference genome for T. mandshurica and integrated comparative genomics, gene duplication analysis, RNA-seq across seven floral developmental stages, qRT-PCR validation, carbohydrate measurements and metabolite profiling. Gene family analysis revealed lineage-specific expansion of families involved in carbohydrate metabolism, ion transport and specialized metabolism. Ks and synteny analyses identified an ancient Eocene whole-genome duplication likely shared with Craigia yunnanensis, whereas duplication-mode analysis indicated that subsequent small-scale duplications contributed to lineage-specific duplicate retention. Among the enriched carbohydrate-related categories, trehalose-phosphatase activity provided a link between genome evolution and floral sugar accumulation. Sixteen trehalose-phosphate phosphatase (TPP) genes separated into fructose-positive C1 and fructose-negative C2 classes, with strong divergence at both the gene level (Δ = 1.060) and module level (Δ = 1.294). C1 TPP genes tracked fructose accumulation, whereas C2 genes followed starch-related developmental programs. Coexpression analysis further revealed contrasting network architectures: C1 TPP genes formed a convergent network with enriched vacuolar/tonoplast-related targets, whereas C2 genes showed a dispersed architecture with no consensus targets. C1-co-expressed candidates included genes related to vacuolar ion homeostasis, cell-wall/glycan remodeling, and isoprenoid/carotenoid metabolism. Together, these results support a model in which duplicated TPP genes are associated with distinct carbohydrate-associated transcriptional programs for starch remobilization and fructose-rich nectar formation. This study provides a genomic resource for Tilia and identifies candidate TPP-centered networks for nectar sugar accumulation in woody honey plants.

Kandelia obovata and Kandelia candel, two sister mangrove species within the genus Kandelia (Rhizophoraceae), exhibit pronounced differences in cold tolerance. However, the genetic basis underlying this adaptive divergence remains unclear. In this study, we assembled a high-quality, chromosome-level genome of K. candel (~225 Mb) to facilitate comparative genomic analysis with K. obovata. Functional enrichment revealed that expanded gene families in K. candel and contracted families in K. obovata were both significantly associated with transcription factor (TF) activity, highlighting TFs as potential key drivers of adaptive evolution. Using whole-genome resequencing data from 53 accessions across representative geographic ranges, we investigated population structure and identified genomic loci associated with environmental adaptation in K. obovata. Notably, temperature-responsive TFs were found to be involved in the circadian rhythm pathway. Through integrated genomic and transcriptomic analysis, we prioritized 18 circadian rhythm-related TFs, including PIF3, CCA1, LHY, and MYB family members such as PAP1, as high-priority candidates linked to cold adaptation in K. obovata. Enrichment analysis of the target genes regulated by these TFs further underscored the importance of flavonoid and phenylpropanoid metabolism under cold stress. Our results suggest that circadian rhythm genes, through their regulation of specialized metabolism, represent promising candidate regulators that may contribute to cold adaptation of K. obovata. This study provides not only key insights into the evolutionary mechanisms of mangrove cold resilience but also a valuable genomic resource for guiding conservation and assisted migration strategies under climate change.

Resin canals are tunnel-like tissue structures primarily responsible for synthesizing and secreting resin. They consist of specialized secondary metabolite-synthesizing epithelial cells and supportive subsidiary cells, which are arranged to form distinctive intercellular spaces. In conifers, resin canals can develop during normal development or be induced by environmental stimuli, which often form an interconnected network and play a crucial role in defense against pathogens and insects. Despite their importance in resin secretion and defense, the mechanisms underlying their formation and function remain poorly understood. In this review, we summarize recent advances in the study of resin canals in conifers from the perspectives of cellular development, defense mechanisms, and molecular regulation. We analyze the distribution patterns, subcellular characteristics and formation and developmental processes of resin canals across different conifer species. Based on studies of traumatic resin canals, we propose a developmental model that depicts the initiation from cambial activity to cell differentiation and canal formation. Furthermore, we focus on resin canal-specific genes and analyze the functions and expression patterns of identified related genes. With the advancement of conifer genome sequencing and single-cell technologies, future research on resin canal regulatory mechanisms and functions is facing unprecedented opportunities. We propose a strategic framework aimed at enhancing conifer breeding, particularly for traits such as stress resilience, disease resistance and wood quality.

Chilling requirement (CR) fulfilment is critical for successful flowering in temperate fruit trees. In mild-winter regions, several anomalies can occur when the cultivar-specific CR is not fully met, including irregular budbreak, bud abortion, and ultimately reduced fruit set. In this study, we examined the molecular regulation of dormancy release in three apricot (Prunus armeniaca L.) cultivars grown under contrasting climates (warm vs. cold/mild winters). We focused on Dormancy-associated MADS-box (DAM) genes and Flowering Locus T (FT) gene using RT-qPCR to evaluate their potential as molecular markers for endodormancy release and indicators of cultivar adaptability. Under moderate differences in chill accumulation between sites, gene expression patterns generally exhibited genotype-specific responses to chilling. Expression of DAM4-6 correlated with prolonged cold exposure and was progressively downregulated towards dormancy release. Faster DAM downregulation in warmer sites corresponded to shallower dormancy and earlier release, consistent with the forcing-shoot experiment results. Among these genes, DAM4 required greater chill exposure for downregulation and emerged as a potential physiological indicator of the transition from endodormancy to ecodormancy, downregulating once approximately 75% of cultivar-specific CR had been fulfilled. However, DAM expression showed limited variation among areas during the later stages, even though substantial differences were observed in the number of viable buds and fruit set in the high-chill cultivar. By contrast, FT expression appeared more sensitive to insufficient chilling in this cultivar. These findings suggest that DAM genes are reliable markers of endodormancy progression, whereas FT may serve as an indicator of flowering quality under suboptimal chill accumulation. Integrating molecular, phenological and climatic data could enhance predictions of endodormancy release and flowering success and facilitate the development of climate-resilient apricot cultivars and adaptive orchard management strategies under global warming.

High temperature has a significant impact on plant reproductive development, driving the formation of 2n gametes by interfering with the meiosis and cytokinesis of sporocytes. This study used Camellia meiocarpa as the material, integrating cytological and molecular biology approaches to reveal the cytological effects and regulatory mechanisms of high temperature on sporocyte development. The results showed that meiosis in microsporocyte and megasporocyte of C. meiocarpa exhibits pronounced spatiotemporal heterogeneity. High temperature markedly disrupted sporocyte development and induced abnormal phenomena, inducing disordered cytokinesis, leading to the formation of dyads, triads in microsporocyte, as well as multinucleate cells occurring during the development of megaspores into mature embryo sacs. RNA-seq sequencing analysis indicates that the CoNPK1 gene may regulate meiotic and cytokinetic behavior in response to high temperature. Meanwhile, heterologous transformation in tobacco verified that the CoNPK1 gene induces the formation of dyads and triads through upregulated expression, which further leads to the production of 2n gametes. We speculate that the CoNPK1 gene regulates cell plate synthesis via the mitogen-activated protein kinase (MAPK) signaling pathway, thereby affecting cytokinesis and generating 2n gametes. This lays a theoretical foundation for ploidy breeding of woody oil crops.

Phosphorus (P) is essential for plant physiological function, yet how P allocation among leaf fractions shapes trait responses in subtropical forests remains unclear. Phosphorus (P) is an essential nutrient for plant photosynthetic and physiological functions. In subtropical ecosystems where P is limited, the allocation of P among different functional fractions in leaf is a potentially adaptive strategy for plants to cope with low soil P availability. However, the effect of imbalanced anthropogenic P input on leaf P fractions and their contributions to leaf functional traits remains unclear. Here, we investigated the effects of P additions (0, 25, 50, and 100 kg P ha-1 yr-1) on leaf P allocation, photosynthetic, hydraulic and water-relation traits in two dominant tree species (Schima superba and Magnolia Sumatrana) and two shrub species (Melicope pteleifolia and Psychotria rubra) within a nutrient addition experiment platform in a subtropical forest. With P additions, leaf total P concentration markedly increased in trees and shrubs; metabolic P proportion increased in trees; inorganic P concentration increased in shrubs. However, P addition did not increase the photosynthetic rate or the maximum leaf hydraulic conductance in any species. Tree species showed more negative turgor loss points and higher bulk modulus of elasticity with P addition. Furthermore, S. superba exhibited significantly lower relative water content and higher relative water deficit at the turgor loss point, while no significant response was observed in M. sumatrana, P. rubra, and M. pteleifolia under P addition. These results indicate cellular adjustments that enhance turgor maintenance and mechanical support, potentially contributing to the stabilization of leaf water relations. Although P addition did not affect leaf water-relation traits in shrub species, it increased leaf mass per area. These results indicate that P addition alters leaf P allocation and water-relations traits in a species-dependent manner. Predicting forest responses to P addition will therefore require species-specific trait-based approaches rather than assuming uniform ecosystem-wide effects.

As alpine forests face increasingly intensified thermal and hydric constraints under climate change, understanding species-specific ecophysiological responses to environmental drivers across altitudinal habitats is essential. Yet whether coexisting evergreen and deciduous conifers adopt contrasting carbon-water regulation strategies under altitudinal stress remains unclear. We examined seasonal gas exchange dynamics in mature spruce (Picea meyeri) and larch (Larix principis-rupprechtii) across contrasting altitudes in the Luya Mountain, northern China. Net photosynthetic rate (Pn), stomatal conductance (Gsw), and leaf water potential (Ψl) were monitored throughout the growing season to quantify how stomatal behavior and environmental drivers regulate carbon-water coordination. At lower altitudes, both species exhibited similar seasonal dynamics, with vapor pressure deficit emerging as the primary constraint, indicating convergence in carbon-water coordination under relatively favorable conditions. In contrast, environmental controls on carbon-water regulation differed between species at the treeline: spruce was predominantly temperature-driven and weakly responsive to soil moisture, whereas larch maintained higher Pn and Gsw and responded mainly to soil water availability. These contrasting controls indicate distinct stomatal regulation strategies under treeline stress, with spruce may adopt a more conservative carbon-water balance and larch may exhibit greater regulatory flexibility. Overall, altitudinal stress shapes species-specific carbon-water coordination, promoting convergence at lower altitudes but amplifying functional divergence at the treeline. This mechanistic insight improves predictions of species-specific responses of alpine conifers to ongoing climate change.

Tropical forests in Southeast Asia are among the most biologically diverse ecosystems on Earth and are critical for carbon storage, water regulation, and climate stabilization. Yet, these forests face severe threats from deforestation due to illegal logging, agricultural expansion, and urban development. Conservation efforts and sustainable forest management are thus important in preserving their biodiversity and maintaining ecological functions. Studies on cambial activity in tropical trees provide valuable insights into species-specific adaptation strategies and the process underlying wood development. Unlike temperate forests, where growth rings clearly indicate seasonal patterns, tropical trees exhibit diverse and often irregular growth responses due to indistinct seasonal conditions. The environmental factors influencing cambial activity in trees remain poorly understood, restricting the accuracy of predictive models for tree growth carbon sequestration potential, and climate resilience. This review aims to summarize current knowledge on how climatic factors and phenological events influence cambial activity across different tropical forest types in Southeast Asia. In addition, it identifies the shortcomings in existing research and proposes directions for future studies. By linking cambial activity in trees with environmental factors, this review provides valuable perspectives for ecologists, policymakers, and forest managers seeking to enhance sustainable forest management and conservation strategies in one of the world's most ecologically significant regions.

How warming changes belowground carbon use in woody plants remains poorly understood. Most experiments measure fine-root, root-exudation, and mycorrhizal responses separately, providing limited evidence on how these responses vary together within the same experiment. We synthesized 13 primary publications from 11 independent experiments: eight field, one outdoor pot, and two controlled experiments. Our synthesis showed no significant increase in fine-root biomass or production. Root respiration, mortality, and N concentration increased, whereas root P and non-structural carbohydrate concentrations decreased. Root-exudation measurements were reported differently across studies, limiting direct comparisons. Root-exudation responses also varied with nutrient treatment, season, and warming duration, while exudate quantity and composition did not always change together. Most mycorrhizal studies measured colonization or infection rather than direct plant-fungal carbon and nutrient exchange. Among the mycorrhizal studies included here, an isotope-based C-for-N ratio proxy varied with N source and sampling time. When multiple belowground responses were measured within the same experiment, concurrent increases in fine-root activity, root exudation, and mycorrhizal association occurred only under particular nutrient and temporal conditions and were not a general response to warming. Opposing responses did not demonstrate compensation; no study showed that an increase in one pathway offset a decrease in another in terms of nutrient acquisition or plant performance. Testing whether warming reallocates carbon among fine roots, root exudation, and mycorrhizal fungi will require coordinated measurements of carbon supply, comparable belowground carbon fluxes, plant nutrient acquisition, and competing carbon sinks within the same experiment.

A long-term irrigation experiment in the dry Rhône Valley of Switzerland provides a unique opportunity to examine transgenerational environmental memory effects of persistent drought and irrigation in Scots pine (Pinus sylvestris). Previous work in this system showed that offspring from mother trees exposed to chronic drought (non-irrigated control) versus long-term irrigation differed markedly in growth and survival. Offspring from irrigated mothers grew faster under irrigated conditions but performed poorly under drought, whereas offspring from drought-exposed mothers showed higher growth and survival under drought conditions. While these responses suggested transgenerational environmental memory, the relative contributions of maternal provisioning versus epigenetic mechanisms could not be fully resolved. Notably, mother trees did not differ in genotype, and seed mass did not vary between treatments, indicating a limited role of maternal effects. Here, we tested whether transgenerational environmental memory effects persist after offspring were grown for three years under non-experimental conditions before being re-exposed to experimental hot-drought and irrigation treatments. In contrast to the earlier study, offspring from irrigated mothers did not show higher growth performance under irrigated conditions, indicating that irrigation-related memory weakened during the intervening non-treated phase. Conversely, seedlings originating from drought-exposed mothers consistently exhibited higher carbon assimilation and stem growth than those from irrigated mothers, irrespective of experimental treatment. Gene expression analyses showed differences in the number and identity of differentially expressed genes between offspring of drought- and irrigation-exposed mothers, although we lack data on DNA methylation, histone modifications, or small RNAs. Patterns in primary metabolites broadly mirrored the results of gene expression, with modest differences in osmoprotectants and stress-related compounds. Overall, our results indicate that transgenerational environmental memory effects in P. sylvestris can diminish over time and, depending on the parental and offspring environments, may even result in mismatch and maladjustments.

Bamboo has emerged as a globally significant sustainable resource, playing an increasingly vital role in 'bamboo-for-plastic' initiatives and other green industries. Internode length represents a key agronomic trait that determines fiber yield and processing efficiency in bamboo. To elucidate the mechanisms governing internode elongation, this study investigated Bambusa distegia (Keng & Keng f.) L.C.Chia & H.L.Fung, a species characterized by exceptionally long internodes (over 100 cm). Comparative analysis of growth dynamics with Phyllostachys edulis (Carrière) J.Houz. and Dendrocalamus farinosus (Keng & Keng f.) L.C.Chia & H.L.Fung, and cytological comparison between B. distegia and P. edulis, revealed that B. distegia exhibited a growth duration of ~60 days for its longest internode, compared with ~20 days for P. edulis and ~40 days for D. farinosus, indicating that the extended internodes in B. distegia originate from prolonged growth duration and increased cell number, rather than accelerated elongation rate or enhanced cell length. Integrated histological, transcriptomic and metabolomic analyses demonstrated that sustained cytokinin signaling serves as the key mechanism maintaining prolonged cell division activity. Through weighted gene co-expression network analysis and co-expression network construction, core regulatory factors were identified, including cytokinin biosynthetic enzymes (CYP735A), modifying enzymes (UGT85A), cell cycle regulators (CYCD3/CYCA3) and key transcription factors (ERF, TCP14). This study systematically clarifies the molecular basis of long internode formation in bamboo and provides valuable genetic targets and theoretical support for breeding industrial bamboo varieties with optimized internode structure and enhanced utilization efficiency, thereby promoting sustainable utilization and value-added development of bamboo resources.