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.

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.

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.

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.

Leaf gas exchange is the key driver of forest carbon uptake and directly determines forest carbon sink activity. Additionally, plants release a variety of biogenic volatile organic compounds (VOCs) acting as stress signals of trees. However, continuous hourly resolved measurements of leaf gas exchange and VOC emissions in tall tree canopies are challenging and remain scarce. To this end, we developed a complex in-situ leaf gas exchange measurement system with 24 cuvettes deployed on mature Fagus sylvatica (n=3) and Pseudotsuga menziesii (n=3) individuals in a mixed temperate forest. We additionally measured sap flux density (Js), radial growth and tree water deficit (TWD) to gain a holistic picture of seasonal leaf and stem water and carbon flux dynamics during the summer of 2024. During midsummer, we found a gradual reduction of stomatal conductance (gs) and VOC emissions of sun, but not shade branchlets of P. menziesii in response to moderate atmospheric and edaphic drying. Decreased gs led to a downregulation of transpiration, Js, and carbon isotope discrimination accompanied by an increase in TWD and intrinsic water use efficiency. Leaf gas exchange of shade branchlets remained unaffected due to microclimatic buffering effects. Contrarily, sun leaves of F. sylvatica profited from sunny midsummer conditions and increased leaf gas exchange, whereas shade leaves benefitted from more diffuse light during early summer exhibiting similar carbon assimilation, transpiration and VOC emissions as sun leaves. For both species we found a clear time lag of four to five hours between maximum leaf and stem water fluxes and a delay of up to 20 hours for the recovery of TWD, highlighting the role of stem water reserves. Pronounced seasonal and diurnal differences of leaf gas exchange, stem water fluxes and VOC emissions showed, that continuous data are essential to better understand the variability of ecosystem flux dynamics.

Green leaf volatiles (GLVs), oxygenated compounds released by plants under biotic and abiotic stresses, play essential roles as signaling molecules in plant immune responses. However, the defense mechanisms mediated by these volatiles remain poorly characterized in conifers, particularly regarding Pinus massoniana against the invasive pine wood nematode (PWN, Bursaphelenchus xylophilus). Here, we systematically integrated transcriptomic and metabolic profiles to compare the defense responses of resistant and susceptible P. massoniana following PWN inoculation. Our results revealed the alpha-linolenic acid metabolism showed positively response to PWN infection in resistant P. massoniana. Notably, (Z)-3-hexenol and its ester derivatives, along with the key ADH genes in the linolenic acid pathway, were significantly activated in resistant P. massoniana at 7 days post-inoculation. Tissue-specific expression profiling of PmADH12 and PmADH13 demonstrated that they were crucial positive regulators in response to PWN challenge in resistant P. massoniana. Functional characterization confirmed that overexpression of PmADHs efficiently increases the production of (Z)-3-hexenol and its ester derivative in P. massoniana. And these PmADHs encode enzymes capable of catalyzing (Z)-3-hexenal to produce (Z)-3-hexenol. Furthermore, in vitro bioassays revealed that (Z)-3-hexenol, the primary enzymatic product of PmADHs, effectively inhibited the PWN survival. Our findings provide mechanistic evidence that ADHs-mediated (Z)-3-hexenol biosynthesis constitutes a chemical defense strategy against PWN infestation in resistant P. massoniana.

Pod shattering, in which mature pods split along their dorsal and ventral sutures, has been widely reported in legume crops due to yield losses. However, the pod-shattering behavior of native legumes that have adapted to decreasing precipitation remains poorly understood. In this study, pod-shattering rates, histology, pod wall components, hydrolase activity and transcriptome of the pod ventral sutures were measured in 6 Caragana species adapted to a wide range of mean annual precipitation (MAP) conditions and growing in a common garden. Species from low-MAP environments presented higher pod-shattering rates, which were associated with a more pronounced abscission zone (AZ), more pod wall torsion laps, lower contents of cellulose and pectin, and increased activities and gene expression levels of polygalacturonase (PG) and cellulase (CE). In contrast, species from high-MAP environments presented lower pod-shattering rates, which were associated with the absence of an AZ, lower pod wall torsion laps, higher cellulose and pectin contents, and reduced activities and gene expression levels of PG and CE. This study hypothesizes that pod-shattering synchronizes seed release to match rainfall patterns, offering a new perspective for understanding the natural distribution of legumes adapted to arid environments.

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.

Gibberellic acid (GA) plays a central role in regulating growth, development, and stress responses. Poplars exhibit woody-specific GA regulatory mechanisms due to their long-life cycle, continuous vascular cambium activity, and seasonal dormancy. While the GA biosynthetic pathway is highly conserved between herbaceous and woody plants, key poplar synthesis genes such as KS1 and KS2 show vascular tissue-specific expression. Centered on the GID1-DELLA signaling pathway, GA modulates downstream genes via ubiquitination and interacts synergistically or antagonistically with hormones like IAA, ABA, and JA to regulate poplar growth and stress responses. Under abiotic stress, poplars downregulate GA levels and accumulate DELLA proteins to enhance resistance. During biotic stress, GA integrates with miRNAs and transcription factors, maintaining growth-defense balance through the DELLA-MYC2 module. Addressing current gaps in holistic GA regulatory network studies and weak understanding of biotic stress mechanisms, this review summarizes poplar GA synthesis, metabolism, and signaling pathways, elucidating their roles in woody-specific traits and stress responses. We aim to provide a theoretical support for GA molecular mechanism research in woody plants and forest tree breeding.

Understanding the intra-annual timing of carbon allocation into wood is critical for linking environmental variability to forest carbon sequestration. We quantified the seasonal dynamics of xylem width increase and xylem biomass production in European beech (Fagus sylvatica) in Belgium during two contrasting growing seasons, a year characterized by a severe spring drought and peak summer hot drought (2020) and a mesic year (2021), using high-resolution X-ray micro-computed tomography (XμCT). Point dendrometer and microtomy measurements were used for validation and comparison. Both xylem width increase and cumulated xylem biomass production followed a sigmoidal seasonal trajectory in both years. Contrary to patterns commonly reported for conifers with a clear early- to latewood transition, the temporal lag between xylem width increase and xylem biomass production was minimal (< 3 days) and statistically insignificant, indicating near-synchronous development. XμCT-derived measurements of ring width, wood density, and biomass production broadly matched dendrometer data, as well as independent regional biomass estimates from the literature. Seasonal onset and cessation of xylogenesis shifted between years, with earlier onset and cessation in the dry year, which was aligned to microtomy data. Our results demonstrate that, in semi diffuse- to ring-porous angiosperms like beech, xylem expansion and secondary wall formation are tightly coupled, even under contrasting water availability, and suggest that dendrometer data can serve as a proxy for intra-seasonal wood biomass production at the stand level. XμCT provides a reliable tool for quantifying xylogenesis and carbon allocation, offering new insights into wood formation dynamics under variable environmental conditions.

Biochar addition promoted cadmium (Cd) phytoremediation of woody plants, especially phosphors (P)-modified biochar. However, the underlying mechanism on the uptake and transport of Cd mediated by biochar remains unclear. Here, we integrated the physiological, metagenomics, transcriptomics, and in situ laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) imaging analysis to investigate how bamboo biochar (BBC) and phytic acid modified biochar (PABC) impact Cd accumulation and transport in Salix J1010 through root-soil interface. Our results showed that PABC significantly increased Cd translocation from roots to aboveground by 77.9% and total Cd accumulation in plan by 203%, respectively. Iron plaque emerged as a key factor, with PABC-mediated inhibition of iron plaque (-44.6%) accelerating Cd uptake. This iron plaque decrease is closely accompanied by the decreased soil redox potential (Eh), enriched resin-P and inorganic P fractions, and potential coupling of P mineralization and Fe(III)-reducing processes in the rhizosphere soil. Transcriptomics analysis further revealed that PABC influenced root metal transporter expression, downregulating vacuolar sequestration-related ABC, CAX, MTP gene families, while upregulating most ZIP, HMA, and YSL genes families involved in xylem loading. LA-ICP-MS imaging corroborated the enhanced Cd transport in xylem tissue. PABC enhanced leaf cell-wall Cd binding and antioxidant defenses, thereby promoting Cd detoxification and accumulation. Collectively, the enhanced phytoremediation capacity of willow was driven by coordinating trade-offs across multiple levels, including the rhizosphere, subcellular scales, and whole-plant. The results provide a mechanistic basis for biochar-assisted phytoremediation strategies in Cd-contaminated soils.