Catalpa bungei is a precious timber species endemic to China, and its congeneric species Catalpa lutea possesses higher economic value due to its distinctive golden-yellow heartwood. To elucidate the metabolic and molecular mechanisms underlying the heartwood color difference between C. lutea and C. bungei, as well as the potential associations between heartwood color and wood properties, we conducted metabolomic and transcriptomic analyses on the sapwood, transition zone, and heartwood of 21-year-old C. bungei and C. lutea trees, and systematically evaluated their wood anatomical structure, physical and mechanical properties, and decay resistance. The results showed that compare with C. bungei, 17 chromogenic metabolites (ten quinones, six flavonoids) were significantly accumulated in the heartwood of C. lutea, among which α-lapachone derivatives (especially 9-hydroxy-α-lapachone and 4,9-dihydroxy-α-lapachone) accounted for 69.99% of the total chromogenic substances, representing the major color-contributing compounds in C. lutea heartwood. Through GO enrichment analysis and expression profiling, five CbuCYP450 genes with hydroxylation functions, namely CbuCYP86A1 (evm.TU.group330.7), CbuCYP82A3A (evm.TU.group3.584), CbuCYP82A3B (evm.TU.group3.585), CbuCYPH3 (evm.TU.group11.1088), and CbuCYP71D95 (evm.TU.group11.1150), respectively, were identified as highly expressed in the transition zone of C. lutea, potentially involved in the hydroxylation steps of α-lapachone derivative biosynthesis. Wood property measurements revealed that, compared with C. bungei, C. lutea possessed significantly higher double wall thickness and wall-to-lumen ratio in fiber cells, as well as significantly superior wood density, hardness, compressive and tensile strengths, and natural decay resistance. Collectively, whose biosynthesis may be associated with the high expression of CbuCYP71D95 and other CbuCYP450 genes. Furthermore, the anatomical structure characterized by thick-walled and narrow-lumened cells, together with the abundant secondary metabolites, jointly endow C. lutea with excellent mechanical properties and decay resistance. This study provides a theoretical foundation for the color-targeted breeding of C. bungei and C. lutea and for the high-value genetic improvement of precious timber species.
Rising atmospheric carbon dioxide (CO2) concentration are a primary driver of global warming and are expected to be associated with more frequent droughts, greater temperatures, and increased vapour pressure deficit (VPD). These factors are all key drivers of tree mortality. While elevated CO2 (eCO2) enhances photosynthesis (Anet) and intrinsic water use efficiency (iWUE), its capacity to mitigate heat stress in mature trees under field conditions remains poorly understood. We investigated the effects of eCO2 on the physiological and growth responses of mature Quercus robur (~180 years old) at a forest Free Air Carbon Enrichment (FACE) experiment. We combined measurements of tree growth, canopy conductance and leaf gas exchange, together with leaf morphological traits, collected during a naturally occurring heat events (> 32°C), to assess whether eCO2 buffered the impacts of extreme heat events (>32°C). The leaf-level measurements also enabled us to determine whether the physiological enhancements previously observed during the early years of BIFoR FACE were maintained following prolonged exposure to elevated CO2. After eight years of CO2 enrichment (+ 150 ppm above ambient), eCO2-grown trees showed increased iWUE (+ 33 %), driven by increased Anet (+ 26.1 %) and modest reductions in stomatal conductance (- 11.1 %), with no significant changes in stomatal anatomy. Elevated CO2 increased the sensitivity of canopy-level conductance to VPD during heat events, indicating stronger stomatal regulation under high atmospheric demand in eCO2 compared to aCO2-grown trees. Heat stress reduced tree growth in both conditions, but the reduction was less pronounced under eCO2, suggesting partial mitigation of heat stress effects. These findings indicate that eCO2 can confer partial physiological buffering against heat stress in mature Q. robur, enhancing resilience without compromising structure. Shifts in water use highlight the importance of integrating CO2-climate interactions when predicting forest responses to future climate extremes.
Trichoderma has proved to enhance plant growth under saline stress. However, there is limited research on Trichoderma-induced alterations of rhizosphere microbial communities in woody plants, and the subsequent effect on their yield is poorly understood. This study was to investigate the growth-promoting mechanism of Trichoderma asperellum on wolfberry (Lycium chinense) in coastal saline land from bacterial community and diversity aspects through a field trial with Trichoderma agent application. Trichoderma agent application significantly increased fruit yield, plant dry weight and nitrogen accumulation, demonstrating that Trichoderma enhanced salt tolerance of wolfberry. Despite no obvious influence on the structure of bacterial community, Trichoderma agent application significantly increased rhizosphere soil bacterial diversity, with beneficial bacterial genera including Shinella and Flaviaesturariibacter showing increased relative abundances. In addition, Trichoderma agent application enhanced the stability of soil bacterial co-occurrence network, as evidenced by higher counts of nodes and edges in the network. Furthermore, Trichoderma agent application reduced the abundance of the complete nitrifier Candidatus Nitrospira nitrificans, inhibited soil nitrification and significantly increased soil ammonium nitrogen content, contributing to the improvement of plant nitrogen nutrition. According to random forest analysis, the most significant predictive importance for wolfberry yield was Shannon index, followed by the relative abundances of beneficial bacteria and soil nitrate nitrogen content, highlighting that the growth-promoting role of Trichoderma could be realized by elevating rhizosphere soil bacterial diversity. Moreover, SEM indicates that in contrast to the pathway of nitrogen accumulation, the increased yield was primarily achieved by enhancing rhizosphere soil bacterial diversity with Trichoderma agent application. Therefore, Trichoderma promotes wolfberry growth and yield in saline land mainly by elevating rhizosphere bacterial diversity, with improved nitrogen nutrition providing an additional contribution. This study deepens our understanding of the mechanisms by which Trichoderma promotes plant growth, and provides a promising biostimulant for wolfberry cultivation in saline land.
Plants are often assumed to optimize carbon assimilation against water loss through stomatal regulation, responding instantaneously to varying atmospheric demand and soil water supply. However, a growing body of work highlights the importance of nighttime recovery processes for understanding plant water use. Yet nighttime processes are not considered in existing supply-demand models. Here, we extend an existing supply-demand model by including flux imbalances between atmospheric demand and soil supply buffered by plant water storage. The flux imbalances accumulate during the day and are compensated overnight. Applying the conceptual model to field data from Quercus pubescens, we show that progressive soil drying constrains the rate of nighttime rehydration. Precisely, below a critical soil water potential threshold (ψsoil,crit), nighttime rehydration begins to decline because rehydration rates become too low relative to the duration of the night ("the night is not long enough"). This threshold marks a transition beyond which maintaining high transpiration rates becomes increasingly risky. The observations show that stomatal regulation begins near this threshold, pointing to the concomitance between daytime stomatal regulation and limited nighttime rehydration. These results suggest that progressive soil drying constrains nighttime rehydration and reveal a critical hydraulic threshold that coincides with the onset of stomatal regulation and highlight that plant water use is constrained not only by daytime fluxes, but also by nighttime recovery.
Belowground carbon (C) allocation by trees particularly through root exudation is a key pathway influencing long-term C storage in forest soils. Future climate change scenarios, such as drought and elevated CO2 (eCO2) strongly affect trees' physiology and influence belowground C allocation. However, how the rate and chemical composition of root exudation change especially under the combined effect of drought and eCO2 remains poorly understood. We conducted an experiment to examine the single and combined effects of drought and eCO2 on the belowground C allocation of Pinus brutia saplings. Root exudates were collected, quantified, and metabolically profiled. Our results revealed that under eCO2, C assimilation increased up to 2.2-fold, increasing plant biomass while root exudation rate and composition remained unchanged under eCO2 compared to ambient CO2 (aCO2). Additionally, when trees were exposed to drought stress, root exudation rate increased 4.3-fold under aCO2, and up to 10.4-fold when combined with eCO2; however, overall, eCO2 had no effect on root exudation. Root starch reserves decreased under drought, whereas soluble sugars increased, with the largest increase under combined drought and eCO2. Further, drought altered exudate composition, increasing several metabolites, mainly phenolic acids (e.g., gallic acid and caffeic acid), amino acids and key osmoprotectants such as trehalose, proline and betaine. Overall, these observations show that pines strongly increased their root exudation under drought and that exudate metabolites shifted towards more specialized metabolites linked to stress metabolism.
Heatwaves and droughts are intensifying, increasing atmospheric evaporative demand and threatening forest functioning. Rising temperatures drive strong declines in photosynthesis and stomatal conductance, yet some trees maintain transpiration during extreme heat via a phenomenon termed stomatal decoupling. However, its occurrence and significance under long-term drought remain poorly understood. We investigated leaf physiology and canopy temperature in a Mediterranean Quercus ilex forest exposed to more than 20 years of experimental rain exclusion, including during an intense heatwave (>40°C). Despite similar soil moisture, experimentally droughted trees experienced lower leaf water potential during the summer. Photosynthesis (Anet) and stomatal conductance (gs) were similar across treatments early in the season. During the heatwave, Anet declined to zero while gs stayed positive, demonstrating strong stomatal decoupling in both drought histories. This decoupling only marginally reduced canopy temperature, which exceeded air temperature by up to 10°C. While foliar thermal tolerance thresholds (>53°C) were not surpassed, extensive canopy damage was observed, especially in experimentally droughted trees, and reduced post-heatwave physiological recovery. Overall, Q. ilex exhibited stomatal decoupling under extreme heat, but this mechanism provided limited evaporative cooling and did not prevent canopy scorching. Long-term drought mainly influenced recovery capacity rather than the occurrence of decoupling itself.
Nutrient deposition is reshaping forest productivity, yet the physiological mechanisms linking nitrogen (N) and phosphorus (P) enhancement to tree growth remain incompletely resolved. We propose that internal resource allocation strategies-specifically intra-organ trade-offs between water and carbohydrate resources and inter-organ carbohydrate concentration gradient-mediate nutrient-driven tree growth responses. Using a long-term fertilization experiment in subtropical Cunninghamia lanceolata plantations, we measured relative water content (RWC) and traditional resource concentrations [soluble sugar (SS) concentration; starch (ST) concentration] during drought season. We rank-transformed RWC, SS, and ST within each organ type across all samples. Intra-organ water-carbon trade-offs were quantified as two normalized ratios: ln(RWCrank/SSrank) for RWC:SS and ln(RWCrank/STrank) for RWC:ST, where higher values indicate greater solute dependence for turgor maintenance or greater ST storage volume fraction, respectively. The inter-organ carbon concentration gradient was quantified as differences in SS or ST between leaves and twigs (SSleaf-twig, STleaf-twig) and between absorptive roots and transport roots. We demonstrated three key nutrient-specific responses: (i) N addition promoted transport root ln(RWCrank/SSrank) while enhancing leaf ln(RWCrank/STrank), amplifying STleaf-twig; (ii) P addition reduced leaf and twig ln(RWCrank/SSrank); and (iii) combined N+P addition reduced twig ln(RWCrank/SSrank), while increasing leaf and twig ln(RWCrank/STrank). These reorganization patterns had direct growth consequences: while traditional resource concentrations explained 26.0% of growth variation, incorporating derived attributes increased explanatory power by 43.5% (to 37.3% total variance explained). Notably, the twig ln(RWCrank/STrank) emerged as the single strongest growth predictor, where N+P induced ST dominance correlated with enhanced growth rate. N enrichment enhanced SS dominance in transport roots, a pattern that may occur at the expense of stem growth. Our results establish an internal resource allocation framework that mechanistically links nutrient-mediated carbon management patterns to forest productivity under global change, revealing how N+P co-enrichment synergistically optimizes carbon resource storage and utilization beyond single-nutrient effects.
Phosphorus is a key nutrient limiting terrestrial ecosystem productivity, with low phosphorus availability affecting over 30% of agricultural and forest ecosystems worldwide. Root development plays a central role in enhancing phosphorus uptake efficiency in plants, with root number being a major determinant of adaptation to phosphorus-deficient. Chinese fir (Cunninghamia lanceolata) cuttings originating from the same clone were used in this study. Root phenotyping, exogenous inhibitor treatments, and transcriptome sequencing were conducted to elucidate the mechanisms underlying root responses to phosphorus limitation. Under phosphorus-deficient conditions, seedling root number was 24.8% and 32.7% higher than in the phosphorus-sufficient at a lower level, and phosphorus-sufficient at a higher level, respectively. The calmodulin protein ClCaM2 was also markedly downregulated under phosphorus-deficient conditions. Inhibition of ClCaM2 expression by an exogenous inhibitor increased root number by 26.4% and significantly enhanced root length and surface area by 26.1% and 31.8%, respectively. Treatment with the exogenous inhibitor also led to the upregulation of phosphate transporter genes (1.5-fold) and key auxin signaling genes, suggesting strong growth-promoting effects. In contrast to wild-type seedlings, transgenic white poplar seedlings overexpressing ClCaM2 exhibited reductions in root length, number, surface area, and volume. Thus, ClCaM2 was shown to participate in adaptive Chinese fir root responses to phosphorus deficiency by negatively regulating root development and moderating the expression of phosphate transporter genes. These findings extend our understanding of the molecular regulation of tree root responses to nutrient stress and provide a potential strategy for improving plant tolerance to low-phosphorus stress through the targeted regulation of calcium signaling.
Whole wood can be used as a practical alternative to α-cellulose in tree-ring 13C isotopic (δ13C) analysis. However, the consistency of the relationships between δ13C of whole wood (δ13CW) and α-cellulose (δ13CC) and their climatic sensitivity can vary across contrasting forest stand structures in tree species composition and along an eco-climatic gradient. We assessed whether δ13CW captures inter-annual variation and climatic sensitivity that are comparable to those obtained from δ13CC of Pinus sylvestris L. The study was conducted across three monospecific and two mixed-species forest stands spanning Mediterranean, temperate and continental-temperate climates. Using 145 individual tree rings from 15 trees, we analyzed offset and correlation between δ13CW and δ13CC, centered around two site-specific pointer drought years (1983 and 2014), including the 2 years before and after drought. Bootstrapped correlation and linear mixed-effect models were used to evaluate and compare the climatic signal strength between δ13CW and δ13CC across the study sites and among monospecific and mixed-species forest stands. Across sites and stand species composition types, δ13CW and δ13CC exhibited significantly different δ13C values, with a constant offset of 1.3‰ (±0.13‰ standard deviation). δ13C values were strongly correlated (91-98%) for the two substrates, showing comparable inter-annual variation and similar sensitivity to climatic factors. We conclude that δ13CW appears to be a reliable alternative to δ13CC under our eco-climatic and forest structural conditions. Our results confirm previously reported strong correlations and stable offset between δ13CW and δ13CC in P. sylvestris. By demonstrating this consistency across contrasting stand composition and wide climatic gradients, our study adds empirical support for the use of δ13CW when cellulose extraction is not feasible. δ13CW is a faster, less labor-intensive and more cost-effective alternative method to quantify, based on pointer years, the effects of water stress on tree growth in large-scale spatial dendro-isotopic studies at the level of annual resolution.
Cadmium (Cd) contamination of orchard soils threatens tree growth, fruit quality and food safety, and strategies are needed to limit Cd accumulation in apple. Grafting is widely used in apple production, but how rootstock-scion interactions regulate Cd uptake and detoxification remains unclear. This study aimed to elucidate the physiological and molecular mechanisms by which different apple graft combinations modulate Cd accumulation and tolerance. Four graft combinations comprising 'Hanfu' (HF) or 'Fuji' (FJ) scions grafted onto Malus baccata (L.) Borkh. (Mb) or Malus micromalus Borkh. (Mm) rootstocks, were grown in nutrient solution with or without 50 μM CdCl₂. Plant growth, Cd2+ influx, Cd accumulation and localization, antioxidant capacity, cell wall composition, and root and leaf transcriptomes were analyzed. Cadmium stress reduced biomass, root system development and photosystem II efficiency but generally increased non-enzymatic antioxidant capacity. The Mb rootstocks showed lower root net Cd2+ influx, lower Cd accumulation in roots and leaves, and weaker Cd signals in xylem than Mm, indicating a greater ability to restrict Cd uptake and transport. Across combinations, root cell walls were the major Cd sink, and Cd exposure increased pectin, hemicellulose and lignin contents. Transcriptome analyses revealed rootstock and scion specific Cd responses, with distinct enrichment of genes related to photosynthesis, oxidative stress and cell wall metabolism. These findings provide a physiological and molecular basis for selecting low-Cd apple graft combinations.
Human activities are intensifying heatwaves and droughts, threatening forest ecosystems worldwide. However, understanding intraspecific variation in physiological traits that confer resistance to hotter drought is critical for predicting tree responses to climate change. In Pinus taeda L., long-term geographic isolation across the Mississippi River Valley after the last glacial maximum has resulted in distinct population genetic structures, likely reflecting historical adaptation to contrasting climatic conditions in western and eastern refugia. However, it remains unclear whether contemporary populations retain meaningful variation in traits that confer tolerance to hotter and drier conditions, such as hydraulic vulnerability and water-use regulation, which are critical for predicting responses to future climate extremes. Here, in a common garden of adult P. taeda trees planted in 2010, we characterized intraspecific variability in 22 physiological traits related to resistance to hotter droughts across 10 provenances originating from either west or east of the Mississippi River Valley. Key traits included xylem vulnerability to embolism, leaf and bark residual conductance, and leaf turgor loss point. We used an integrated indicator, Time to Hydraulic Failure (THF), predicted by a mechanistic hydraulic model, SurEau, to assess how trait combinations contribute to tree resistance to hotter droughts. While we hypothesized that western provenances would be more adapted to hotter drought, we found that THF was lower in western than eastern provenances. The THF values were negatively correlated with residual transpiration and leaf mass per area. These patterns suggest physiological differentiation between populations, although not one strictly determined by drought resistance alone. Overall, our findings demonstrate that intraspecific variation in physiological traits can inform forest management and breeding strategies, underscoring the complex interplay of hydraulic and residual transpiration traits in shaping drought resilience and emphasizing the need to integrate multiple physiological processes when predicting forest responses to climate change.
Cadmium (Cd) contamination is a major environmental concern that threatens plant growth and human health. Poplar (Populus spp.) is a promising candidate for phytoremediation due to its high biomass, extensive root system and strong capacity for heavy metal tolerance and accumulation. Here, transcriptomic profiling identified PyMTP10 as a critical metal tolerance protein gene that was activated by PyWRKY48 and that encodes a metal tolerance protein, and was strongly induced in PyWRKY48-OE poplar under Cd stress. RT-qPCR further confirmed that PyWRKY48 positively regulates PyMTP10 expression. Yeast one-hybrid, dual-luciferase reporter and electrophoretic mobility-shift assay experiments demonstrated that PyWRKY48 directly binds to the W-box cis-element in the promoter of PyMTP10 and activates its transcription. To investigate the function of PyMTP10, we generated PyMTP10-overexpressing and RNA interference transgenic poplar lines. Under Cd stress, PyMTP10 overexpression improved Cd tolerance, as evidenced by increased growth, chlorophyll content and antioxidant enzyme activities. PyMTP10 overexpression also increased Cd accumulation throughout plant tissues, concomitant with elevated levels of glutathione and phytochelatins. This study revealed that the PyWRKY48-PyMTP10 module coordinately regulates Cd tolerance and accumulation in poplar through the integration of transcriptional activation with enhanced chelation and sequestration. These findings expanded our understanding of Cd detoxification mechanisms in woody plants and provided molecular targets for improving phytoremediation efficiency in Cd-polluted soils.
Understanding how trees balance carbon storage, hydraulic function and growth under drought is critical for predicting forest resilience to climate change. However, little is known about the interactive roles of non-structural carbohydrates (NSC), particularly starch and soluble sugars (SS), in coordination with wood anatomical traits and stable isotope signatures in mediating tree responses to drought stress. This study investigates the interplay between NSC, wood anatomical traits and intrinsic water-use efficiency (iWUE) in 56 European beech (Fagus sylvatica L.) trees from different crown conditions across drought and wet years in four sites in northeastern France with contrasted soil water deficit. We followed NSC (starch and SS) content in sapwood of trees each year and analyzed retrospectively tree ring width, vessel anatomy and stable isotopes (δ13C, δ18O). Results revealed that drought years significantly reduced starch content but increased SS, reflecting their role in osmotic regulation and metabolic demands. The SS to NSC ratio increased during drought, highlighting a dynamic carbon reallocation. Growth (tree basal area increment) declined in drought years, with starch accumulation in wetter years and SS prioritizing survival under stress. The SS to NSC ratio correlated positively with vessel density and theoretical specific xylem hydraulic conductivity (Kth), suggesting their involvement in hydraulic maintenance, while starch exhibited a negative relationship with Kth, indicating a trade-off between carbon storage and hydraulic efficiency. Elevated δ13C and iWUE during drought confirmed stomatal closure to conserve water, though at the cost of reduced carbon assimilation. δ18O correlated positively with SS, closely coupling carbohydrate dynamics to altered transpiration. These findings underscore how NSC dynamics, anatomical adjustments and isotopic signals collectively mediate drought responses, offering insights into carbon-water trade-offs in temperate forests.
Nutrient and water supply are decisive limiting factors for trees and their productivity. Yet, the consequences of fertilization for drought responses, especially during the sensitive nursery stage, remain poorly understood. In this study, we exposed potted saplings of Pinus sylvestris L., Fagus sylvatica L. and Quercus robur L. to two levels of fertilization and three water regimes. The effects of fertilization, drought and their interaction on gas exchange, hydraulic traits and growth were examined. Fertilization generally promoted gas exchange, hydraulic conductance and biomass accumulation but responses were species-specific and did not always persist under and after drought. While fertilized Q. robur maintained or even increased its biomass and physiological performance under drought, the benefits of fertilization for P. sylvestris and F. sylvatica diminished under increasing drought intensity. No consistent changes in drought resistance traits (e.g., turgor loss point, embolism resistance) were observed across species in response to fertilization, which may indicate limited plasticity or acclimation potential of saplings. Our findings highlight the species-specific fertilization effects on drought responses and post-drought performance of saplings, emphasizing the need to consider both factors in silvicultural practices under future climate scenarios.
The annual transport patterns of mineral nutrients in conifers remain poorly understood. Calcium (Ca) and magnesium (Mg) deficiencies often occur in planted conifer stands and cannot be easily remedied by simply adding these nutrients to soil. This study examined translocation and remobilization of Ca and Mg in young Nordmann fir (Abies nordmanniana) trees. Our data revealed that Ca and Mg absorbed by the roots do not reach the needles during the current growth season, indicating that internal nutrient remobilization is crucial for the growth of new needles, particularly shortly after the budbreak. Monitoring 1-year-old needles over a full annual cycle revealed steep declines in Ca and Mg around budbreak, coinciding with their increase in the emerging needles on the same branch. This strongly suggests that older needles supply Ca and Mg to new needles. Trees with low Mg concentration in 1-year-old needles in the spring developed visual Mg deficiency symptoms during the summer. For Ca, which is immobile in the phloem, we recorded a substantial increase in the apoplast of older needles just before budbreak. Simultaneously, the immunolocalization of cell wall homogalacturonan in these needles declined, suggesting pectin modification that facilitates Ca release from cell walls, enabling its translocation to the neighbouring, current-year needles. Our findings reveal a previously unknown process that advances understanding of mineral nutrient remobilization in conifer trees.
Climate change affects the physiology and growth of trees, as well as the functioning, health and productivity of forest ecosystems. This also concerns forests dominated by Norway spruce (Picea abies (L.) Karst.), one of the most important tree species in Europe, in both economic and ecological aspects. In the southern part of its range, the growth of spruce trees will be primarily constrained by limited soil water and high atmospheric vapor pressure deficit in the future. However, there is little information on how the trees will respond to increasing precipitation and the concomitant rise in environmental humidity, predicted for high latitudes. In this article, we evaluated the effects of increasing environmental humidity (soil vs atmospheric humidity) on needle morphology, water status and gas exchange in trees in a northern climate, aiming to understand the reasons for the growth decline in response to elevated air humidity revealed in our previous studies. A 15% increase in summer precipitation and the associated change in soil moisture do not considerably affect trees' performance in northern mesic conditions. Growing in increased air humidity (relative humidity elevated by ~5%) did not influence photosynthetic capacity, but it increased the light compensation point of photosynthesis (19.7 → 31.4 μmol m-2 s-1) and dark respiration rate (-0.216 → -0.297 μmol m-2 s-1) of the spruce trees. In light of climate change, both responses reduce photosynthetic output, increasing respiratory losses and reducing the growth potential of trees.
Moso bamboo (Phyllostachys edulis) is a high-value renewable resource used for timber, fiber and carbon sequestration, yet the cellular basis of its development remains poorly resolved. Here, we performed a systematic single-cell RNA-sequencing analysis of moso bamboo seedlings, generating 31,658 high-quality single-cell transcriptomes. Initial unsupervised graph-based clustering partitioned the dataset into 23 clusters, which were subsequently assigned to 11 major cell-type categories through marker-guided and biologically informed annotation, including meristemoid, coleoptile L1 epidermis, cortex, epidermis, mesophyll precursor, mestome sheath, pericycle, phloem, endodermis, root cap and xylem. Pseudo-time analysis suggested putative vascular-associated trajectories in which captured xylem and phloem cells were ordered along a bifurcating structure extending from meristem populations. Xylem cells were enriched in cell wall modification genes, while phloem cells preferentially expressed transport- and defense-related genes. Root cell differentiation exhibited polar patterning, progressing through seven stages from meristems to epidermis, endodermis, cortex and root cap lineages. Leaf development followed a unidirectional trajectory from meristems to mestome sheath cells and coleoptile L1 epidermis, and ultimately to mesophyll cells. We further identified key regulatory factors underlying these cellular differentiations, revealing developmental path differences among roots, stems and leaves. This study constructs a high-resolution cellular atlas of moso bamboo seedlings that delineates developmental programs underlying rapid growth and environmental adaptation, and uncovers dynamic trajectories from meristems to specialized cell types. These findings provide candidate regulators for future genetic studies to enhance biomass production and stress tolerance in moso bamboo.
Nutrient limitation and drought stress often co-occur and jointly influence tree phosphorus (P) acquisition and variation in absorptive root traits. However, it remains unclear whether interspecific variation in P acquisition strategies under combined stress reflects a trade-off between P uptake rate (PUR) and P utilization efficiency (PUE), and how this variation is associated with absorptive root morphology and P uptake kinetic characteristics. Seedlings of four broad-leaved deciduous tree species, Quercus variabilis Blume, Prunus davidiana (Carrière) Franch., Acer truncatum Bunge, and Koelreuteria paniculata Laxm., were grown for 8 weeks in a 3 × 3 factorial experiment with three nutrient limitation levels and three drought severity levels. We then measured total biomass, PUR, PUE, P uptake kinetic characteristics (Vmax, Km and α) and absorptive root morphological traits (root order ≤ 3), including specific root length (SRL), specific root surface area (SRA), root diameter (RD) and root tissue density (RTD). Species exhibited distinct P acquisition strategies under nutrient limitation and drought stress. Acer truncatum and K. paniculata showed a more acquisitive strategy, with higher PUR, greater SRL and SRA, and lower RD and RTD. In contrast, Q. variabilis and P. davidiana showed a more conservative strategy, with higher PUE and denser absorptive roots. Among P uptake kinetic characteristics, α showed the clearest association with these interspecific strategies. We identified a trade-off between PUR and PUE under combined nutrient limitation and drought stress, with tree species differing in the extent to which they relied on uptake versus utilization. These contrasting acquisitive and conservative strategies were associated with variation in absorptive root morphology, with α providing the clearest kinetic link, consistent with a root economic framework for P acquisition under stress.
Schisandra chinensis (Turcz.) is a valuable medicinal woody plant, yet its industrial propagation is constrained by the rapid decline in embryogenic competence of callus during in vitro culture. Elucidating the underlying mechanism is essential for establishing a sustainable and efficient micropropagation system. This study aimed to systematically clarify the physiological and molecular mechanisms underlying the decline in embryogenic potential across successive subculture generations in S. chinensis embryogenic callus, thereby providing a theoretical foundation for optimizing the somatic embryogenesis protocol. An integrated multi-omics approach was employed, combining phenotypic, physiological, transcriptomic and metabolomic analyses of callus at key subculture stages (P1, P4 and P7). The results indicate that embryogenic potential is maintained under a state of balanced energy metabolism and redox homeostasis. Highly embryogenic (P4) callus exhibited active energy and amino acid metabolism, supported by up-regulated hub genes (ScACO3, ScENO1, ScHSP70-4). In contrast, prolonged culture induced severe oxidative stress, characterized by the accumulation of H₂O₂ and O₂-. This oxidative burden activated a ribosomal stress response, with significant up-regulation of ribosomal protein genes (ScRPL7B, ScRPS12, ScRPS11B, ScRPL10A, ScRPL10), ultimately leading to proteostatic collapse and loss of embryogenic capacity. We propose that an 'energy-redox-ribosome axis' serves as the core regulatory cascade determining cell fate under culture stress. These findings identify novel targets for delaying embryogenic decline through antioxidant supplementation and culture regimen optimization, offering a sustainable strategy to mitigate in vitro stress in the propagation of woody perennial plants.
