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.

Quantifying ascorbate (ASC) and glutathione (GSH) in woody perennial tissues presents significant methodological challenges due to complex tissue matrices and the lability of these redox-active metabolites. We adapted established enzymatic microplate assays for ASC and GSH quantification to mature dormant grapevine buds, a structure containing protective scales, hairs, and lignified components. Key optimisations included: (1) use of 1 M HClO4 rather than 0.2 M HCl for effective enzyme inactivation and matrix disruption; (2) sample to solvent ratios of 1:10 to 1:15; and (3) extended centrifugation to effectively sediment organic components. Standard addition experiments revealed significant matrix effects, with recovery of approximately 80 % for ASC and 65 % for GSH. The optimised method successfully determined >90 % reduction status for both metabolites in mature buds. Critically, we observed severe ASC instability during frozen storage, with approximately 80 % loss of ASC after four months at -80 °C, while GSH remained stable. These findings underscore the necessity of immediate analysis for ASC quantification in woody tissues and provide a validated protocol for studying redox metabolism in perennial bud tissues.

Mannans are hemicellulosic polysaccharides integral to plant growth and development, yet their functions in trees and the regulation of their synthesis remain poorly understood. Here, we investigated the biosynthesis of GDP-mannose (GDP-Man), the primary sugar donor required for mannan synthesis. Using phylogenetic analyses, protein domain characterization, and RNAseq-based expression profiling, putative GDP-mannose pyrophosphorylase (GMP) candidates were identified in poplar and spruce. Functional validation of candidate genes was performed by complementation of the Arabidopsis vtc1-1 mutant, and by generating CRISPR/Cas9 knockout and ectopic overexpression lines in poplar. Our results showed that poplar PtaGMP1 and spruce PgGMP1, successfully complemented the vtc1-1 mutant, restoring mannan content to wild-type levels. In poplar, CRISPR/Cas9 knockouts of PtaGMP1 reduced mannan by 20% and ascorbic acid by 47%, whereas ectopic overexpression of PgGMP1 increased mannan by 14% without significantly affecting ascorbic acid content. In both cases, these changes did not significantly affect tree growth. Overall, our study provides new insights into the regulation of mannan biosynthesis in trees and the contribution of GMPs to both mannan and ascorbic acid production in poplar.

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. 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 and2014), including the two years before and after drought. Bootstrapped correlation and linear mixed-effects 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 labour-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.

Thigmomorphogenesis, the process by which plants acclimate to mechanical stress through growth modulation, significantly affects biomass allocation but remains underrepresented in integrative tree response models. Specifically, the contribution of chronic, non-injurious wind-induced strains to growth acclimation remains poorly quantified in natural environments. We characterized the secondary growth response to experimental strain stimulus in the stems of Pinus pinaster under forest conditions. Eighteen 12-year-old trees were subjected to transient bending treatments replicating the range of trunk strains generated by local chronic winds, while six trees served as controls. Radial growth was monitored continuously at three trunk positions. The thigmomorphogenetic response was quantified using growth rate amplification and cumulative growth gain, then related to the estimated strain intensity at each position. Mechanical strain induced an immediate, sustained increase in radial growth along trunks. This stimulation persisted over extended periods, pausing only during drought or winter before resuming. Growth modulation scaled proportionally with strain intensity across the full natural range, with no detectable threshold. A consistent strain-response relationship was observed across all trunk positions, indicating spatially homogeneous sensitivity. These results demonstrate that secondary growth in P. pinaster is sensitive to the full spectrum of chronic wind-induced strains. This supports the view that non-injurious winds drive continuous mechanical acclimation contributes to a growth-mediated margin of safety in trees.

Global warming pushes plants close to their leaf thermal limits, altering carbon uptake, growth and survival. Therefore, investigating leaf thermal tolerance adjustment is essential to understand future vegetation dynamics, especially in high-risk Mediterranean shrubs facing hot and dry summers. We measured dark-adapted leaf fluorescence (Fv/Fm), thermal thresholds (Tcrit, T50, Tmax), optimal assimilation temperature (Topt), thermal safety margin (TSM), leaf and air-temperatures (Tair, Tleaf) and gas exchange (A, gs, E) in six shrub species in six sites along a climatic gradient in Catalonia, Spain. Across all species, we found that Topt increased as conditions warmed, while Fv/Fm and Tmax showed quadratic responses decreasing in the warmest sites. Hence, TSM declined and approached 0 at the hottest sites, indicating that shrubs were operating close to their thermal limits. Warmer Tair under high levels of solar radiation raised Tleaf, though some species occasionally maintained Tleaf < Tair during daytime, suggesting a passive or active leaf cooling at high temperatures. Moreover, E and, to a lower extent, gs remained relatively high despite low A at higher Tleaf (at a given VPD), revealing a partial decoupling of gas exchange at high temperatures. Incorporating leaf thermal tolerance adjustments and gas exchange decoupling at extreme temperatures into vegetation models could improve predictions of shrub function and dynamics under warmer climates.

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 (Mb) or M. micromalus (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. Cd stress reduced biomass, root system development, and PSII efficiency but generally increased non-enzymatic antioxidant capacity. 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.

Branch water release and radial exchange influence drought responses. Although mechanistic models describe radial hydraulic and storage dynamics, experimental quantification of hydraulic capacitance (C) and radial resistance (Rr) across broad ranges of xylem water-potential (Ψx), particularly under severe dehydration, remains limited. We quantified how C and Rr vary with Ψx in Populus alba, assessed the value of coupling controlled osmotic dehydration with high-resolution dendrometry, and evaluated cellular damage and bud viability across increasing dehydration levels. Branch segments were subjected to stepwise, experimentally induced dehydration by perfusion with D-sorbitol solutions (-1 to -4 MPa) to impose stable and controlled Ψx. Branch diameter dynamics and equilibration plateaus were used to estimate C and Rr, and diameter-derived pressure-volume curves were fitted using the Sureau model. Electrolyte leakage (EL) and bud development were monitored to assess injury and recovery capacity at the organ level. D-sorbitol equilibrated rapidly along the xylem with limited bark infiltration, and stepwise decreases in Ψx induced characteristic diameter contractions enabling robust extraction of C and Rr. Both traits varied with Ψx: C peaked at intermediate Ψx (-1 to -2 MPa) and declined under severe dehydration, while Rr increased steadily as Ψx decreased. EL increased and buds failed to resume growth below -2 MPa. Controlled osmotic dehydration combined with high-resolution dendrometry enables precise quantification of C(Ψx) and Rr(Ψx) and reveals physiologically meaningful thresholds associated with cellular injury and loss of recovery capacity at the organ level, providing a useful framework for dehydration-tolerance phenotyping.

Drought frequency and intensity increasingly threaten tree survival and growth by altering trees carbon (C), nitrogen (N), and water utilization. Yet, the interplay of aboveground and belowground processes during drought recovery remains unclear. We conducted a microcosm experiment with pine (Pinus massoniana), fir (Cunninghamia lanceolata), and oak (Quercus acutissima) saplings, exposing them to three levels of drought intensity (i.e. well-watered, moderate drought, and severe drought) for three months, followed by 30 days of rewetting. Using 13C and 15N isotopes, we tracked C and N allocation. Our results showed that drought-stressed saplings rapidly increased net photosynthesis and predawn leaf water potential after rewetting, with the exception of severely drought-exposed oak. Root N uptake (represented by 15N recovery) also recovered quickly, even surpassing well-watered levels in moderately drought-exposed pine and fir. However, severe drought-stressed pine and fir exhibited significantly lower coarse root non-structural carbohydrates (NSC), while oak maintained higher root and stem NSC. The two coniferous species, previously severely drought-stressed, prioritized C and N allocation to aboveground and had reduced xylem hydraulic conductance after rewetting. The recovery rate of oak was slower, with limited N translocation to aboveground tissues due to leaf abscission. In conclusion, rapid root recovery coupled with more recently photosynthetic C retained in aboveground organ led to root NSC consumption in drought-stressed pine and fir. Conversely, oak's recovery was slower, largely driven by its phenology. This study underscores that aboveground and belowground C and N allocation patterns are closely linked during drought recovery, determined by species-specific traits and the severity of prior drought stress.

Tree crops are essential agroecosystems that contribute to global food security and economic development by providing a variety of fruits, nuts, and other edible products. However, the sustained production of these crops is increasingly threatened by pest and disease (P&D) pressure. Remote sensing (RS) techniques provide non-invasive, scalable tools for monitoring the physiological responses of crops to biotic stressors and for integrated P&D management frameworks. Despite their increased use in recent decades, there remains limited clarity regarding the frameworks, parameters, and spectral variables used to assess tree crop health. This is because earlier reviews focused primarily on food crops and forest trees, paying little attention to tree crops. To fill this gap, we conducted the first systematic review of the peer-reviewed literature to evaluate the scope, opportunities, and methodological approaches for RS applications across a wide spectrum of tree crops. Our findings show that research using RS techniques in tree crop health monitoring has grown consistently since 1974, with studies focusing on citrus, oil palm, olives, and rubber trees accounting for more than half of the reviewed literature (52.73%). Spectral indices derived from both hyperspectral and multispectral data, analysed using machine learning and statistical models, were the dominant approach for monitoring P&D dynamics in tree crops. Geographically, most studies have been concentrated in North America and Eurasia, with limited application in tropical tree crops. Extending the use of RS techniques to economically important tropical tree crops will not only support adaptive responses to biotic threats but also improve yields and sustainability across tree-crop systems worldwide.

Understanding how traits covary and influence growth is key to understanding adaptation in perennial species. In the Mediterranean olive tree (Olea europaea L.), both genetic background and geographical origin may shape trait variability, covariation patterns, and growth strategies, however these relationships remain largely unexplored. We analysed 100 olive varieties, representing four genetic groups and two geographical origins (North vs. South Mediterranean), by measuring eleven morpho-anatomical and physiological traits, and two growth indicators. We combined multivariate analyses, correlation networks, and regression models to explore trait covariation and its impact on growth. Our findings show that trait variation was primarily structured at the varietal level, while both genetic groups and geographic origin significantly shaped covariation patterns and functional integration, with southern-origin varieties tending to exhibit thicker and denser leaves. Trait networks revealed a robust coordination between leaf and stem structural traits, with modularity and connectivity varying across groups. The South group exhibited a more modular network, suggesting more constrained trait integration under arid conditions. At both stem and whole-plant levels, growth was positively associated with leaf area. In contrast, LDMC showed a positive relationship with stem diameter growth but a negative relationship with whole-plant growth, suggesting that different mechanisms underlie short-term stem expansion and long term cumulative growth. Overall, genetic factors, environmental context, and trait coordination jointly structure olive phenotypic diversity. These findings provide a functional framework for guiding the selection and conservation of olive varieties with growth strategies suited to current and future Mediterranean climates.

While vertical forest structure is known to influence microclimatic conditions and tree growth, detailed knowledge of differences in seasonal growth dynamics between understory and canopy trees, especially at fine temporal scales, is still lacking. In this study, we compared growth dynamics of five temperate tree species (Picea abies, Fagus sylvatica, Carpinus betulus, Acer campestre, Ulmus laevis) based on sub-daily measurements from automatic band and pivotal dendrometers across four old-growth forests. Hourly growth probabilities were modelled using Generalized Linear Mixed-Effects Models (GLMMs) in relation to climatic conditions and day phases. Understory trees exhibited shorter growing seasons, accumulated fewer growing hours, and displayed a less distinct diel growth rhythm than canopy trees. Nonetheless, when growth occurred, their growth rate per growing hour, normalized by stem diameter (DBH), was higher. However, overall growth remained constrained, likely because light availability limited the frequency or duration of such favourable periods, preventing consistent utilization of the buffered microclimatic conditions typical of the forest understory. GLMMs successfully captured growth dynamics in canopy trees but performed poorly for understory trees, indicating lower dependency of their growth patterns on climatic conditions. Overall, our results show that understory tree growth is constrained primarily by limited light availability rather than by atmospheric conditions, leading to fewer growth periods that account for a larger proportion of the annual increment compared to canopy trees.