Isoprene emission from plants not only confers thermoprotection, but also has profound impacts on atmospheric chemistry and the climate. Leaf isoprene emission is dynamically regulated in response to various environmental cues, but the exact mechanism remains unclear. It has been proposed that chloroplast redox/energy state or cytosolic phosphoenolpyruvate carboxylation regulates isoprene biosynthesis and consequently emission, and the latter has been disproven by recent literature. However, the possible covariation of chloroplast redox/energy state and cytosolic PEP carboxylation in previous experiments impedes the independent examination of the former hypothesis. We developed an index of chloroplast redox state and showed its validity by examining the relationships between the index and the rates of certain processes which have been demonstrated to be affected or unaffected by chloroplast redox/energy state. According to the former hypothesis alone, we modelled how isoprene emission rate (IER) responded to different short-term environmental variations, and compared theoretical predictions with experimental data. We predicted that no matter which environmental factor was varied, IER would respond to the index of chloroplast redox state with similar velocities. We found that IER showed comparable increasing rates in response to the increase in the index of chloroplast redox state caused by different environmental variations (0.0479, 0.0439 or 0.0319 when ambient CO2 concentration, photosynthetic photon flux density or leaf temperature was varied, respectively). These results support that chloroplast redox/energy state regulates isoprene biosynthesis, leading to dynamic isoprene emission in nature.

The boreal forest ecosystems of the northern hemisphere are dominated by conifers, of which Norway spruce (Picea abies (L.) H. Karst.) is one of the most common species. Due to its economic interest to the agroforestry industry, as well as its ecological significance, it is important to understand seasonal growth and biomass production in Norway spruce. Solid evidence that the circadian clock regulates growth in conifers has proved elusive, however, resulting in significant gaps in our knowledge of clock function in these trees. Here, we reassess the impact of the circadian clock on growth in Norway spruce. Using a combination of approaches monitoring the physiology of vegetative growth, transcriptomics and bioinformatics, we determined that the clock could be participating a decisive role in enabling growth, acting in specific developmental processes influenced by season and geographical location to guide bud burst and growth. Thus, evidences indicate that there is time for spruce.

The severity of droughts is expected to increase with climate change, leading to more frequent tree mortality and a decline in forest ecosystem services. Consequently, there is an urgent need for monitoring networks to provide early warnings of drought impacts on forests. Dendrometers capturing stem diameter variations may offer a simple and relatively low-cost opportunity. However, the links between stem shrinkage, a direct expression of tree water deficit (TWD), and hydraulic stress are not well understood thus far. In this study, we exposed two widespread conifers Pinus sylvestris and Larix decidua to lethal dehydration by withholding water and closely monitored TWD, midday water potential ($\psi $), and midday stomatal conductance ($g_{s}$) under controlled greenhouse conditions. We found strong relationships between the three variables throughout the dehydration process, particularly suggesting the potential for continuous $\psi $ predictions and stomatal closure assessments. However, the relationships decoupled during recovery from severe drought. We also identified TWD thresholds that signal the onset of drought stress and tissue damage, providing insights into stress impacts and recovery potential. While these findings are promising, challenges remain in practically transferring them to field set-ups by suitable TWD normalization. Importantly, we observed that midday $g_{s}$ was drastically reduced when TWD persisted overnight, providing a directly applicable drought stress signal that does not require normalization. In conclusion, while challenges remain, our results highlight the potential of dendrometers for monitoring tree water dynamics. Implementing dendrometer networks could support the development of early-warning metrics for drought impacts, enabling large-scale monitoring in diverse settings, such as urban areas and forest ecosystems.

Amazonian species are generally unable to adapt to long drought periods, indicating a low capacity to adjust their hydraulic traits. Secondary forests account for 20% of forest cover in the Amazon, making natural regeneration species crucial under climate change scenarios. In this study, we compared the hydraulic traits of five species, including non-pioneers (Bertholletia excelsa Bonpl., Carapa guianensis Aubl., Hymenaea courbaril L.) and pioneers (Cedrela fissilis Vell., Tabebuia rosea (Bertol.) Bertero ex A.DC.), across light conditions (understory, intermediate, gap) in a 22-year-old secondary forest in Central Amazon, Brazil. Twenty-five saplings were planted and monitored in 3 plots × 5 blocks. Five years after the plantation, we assessed growth, wood density, leaf water potential at predawn and midday, xylem embolism resistance (P50), and hydraulic safety margins (HSM). Leaf water potential ranged from -2.9 to 0 MPa. The non-pioneer species C. guianensis and H. courbaril exhibited the lowest P50 (-4.06 MPa), indicating higher embolism resistance, whereas the pioneer T. rosea had the highest P50 (-1.25 MPa), indicating lower resistance. HSM varied from -1.60 to 3.26 MPa, with lower values in gap conditions during the dry period (-1.60 MPa), especially affecting pioneer species. Wood density was influenced by both light and species type, with non-pioneers showing generally higher density, with H. courbaril reached 0.75 g cm-3 in the understory while the pioneer T. rosea showed the lowest density (0.27 g cm-3). These results highlight that light conditions affect hydraulic traits differently across species strategies, especially during early growth. Non-pioneer, slow-growing native species appear more resilient to light variation, making them suitable for future plantations aimed at climate adaptation in secondary forests.

Urban Heat Islands (UHI) are a common phenomenon in metropolitan areas worldwide where the air temperature is significantly higher in urban areas than in surrounding suburban, rural or natural areas. Mitigation strategies to counteract UHI effects include increasing tree cover and green spaces to reduce heat. The successful application of these approaches necessitates a deep understanding of the thermal tolerances in urban trees and their susceptibility to elevated urban temperatures. We evaluated how the photosynthetic thermal optimum (Topt), photosynthetic heat tolerance (T50), and key leaf thermoregulatory morphological traits (leaf area, specific leaf area, leaf width, thickness and LDMC) differ between conspecific trees growing in 'hot [UHI]' vs. 'cool' parts of Montreal, Canada (with a difference of 3.4 °C in air temperature), to assess the ability of seven common tree species to acclimation to higher temperatures. We hypothesized that individuals with hotter growing temperatures would exhibit higher Topt and T50, as well as leaf thermoregulatory morphological traits aligned with conservative strategies (e.g., reduced leaf area and increased leaf mass) compared to their counterparts in the cooler parts of the city. Contrary to our a priori hypotheses, leaf area increased with growing temperatures and only four of the seven species had higher T50 and only three had higher Topt values in the hotter area. These results suggest that many tree species cannot acclimate to elevated temperatures and that the important services they provide, such as carbon capture, can be negatively affected by high temperatures caused by climate change and/or the UHI effect. The ability vs inability of tree species to acclimate to high temperatures should be considered when implementing long term tree planting programs in urban areas.

C-repeat binding factors (CBFs) play a pivotal role in regulating cold response in higher plants. Camellia sinensis cv. Baiye 1, a representative albino tea cultivar, has been identified as temperature-sensitive based on long-term observations by tea farmers. However, it remains unclear whether CsCBFs are involved in temperature-mediated albinism and seasonal greening in 'Baiye 1', and the mechanisms by which CBFs regulate cold responses in albino leaves are unknown. In this study, we demonstrate that CsCBF2 suppresses the seasonal greening of albino leaves by inhibiting chlorophyll and carotenoid biosynthesis under cold stress. In tea plantations, the accumulation of chlorophylls and carotenoids in the albino shoots of 'Baiye 1' is closely correlated with the effective accumulated temperature during its seasonal greening process. Weighted Gene Co-expression Network Analysis revealed negative associations between CsCBF expression and chlorophylls, carotenoids, as well as their biosynthetic genes REVEILLE 1 (CsRVE1) and Zeaxanthin epoxidase 1 (CsZEP1) under temperature fluctuations during seasonal greening. Cold-induced upregulation of CsCBF2 expression and decreased chlorophylls and carotenoids under controlled climate conditions. Transient suppression of CsCBF2 by antisense oligodeoxynucleotide elevated expressions of target genes, and increased chlorophylls and carotenoids. CBF-binding cis-elements were identified in CsRVE1, Protochlorophyllide oxidoreductase A (CsPORA), and CsZEP1 promoters. Luciferase assays suggested CsCBF2 binding to the CRT/DRE cis-elements and repressing expression of CsRVE1, CsPORA, and CsZEP1. These findings highlight CsCBF2 as a key transcriptional repressor involved in the seasonal greening of albino 'Baiye 1' under cold stress, by modulating cold responses and inhibiting genes associated with chlorophyll and carotenoid biosynthesis.

Cell totipotency and pluripotency are the cellular basis for root regeneration in Platycladus orientalis cuttings, and the regeneration of adventitious roots is a key determinant for improving stem-cutting. However, the cellular basis and physiological regulation of adventitious root formation are still ambiguous. In this research, root primordia initiation and organogenesis were histologically observed, dynamic alterations in soluble proteins were monitored, and Tandem Mass Tag protein profiling during adventitious root development was carried out. It was explicitly shown that the root primordium primarily originated from undifferentiated xylem cells for indirect (callus) rooting and from dividing cells in the cortex for direct (cortex) rooting. During the entire process of adventitious root development, the activities of peroxidase (POD) and polyphenol oxidase (PPO) peaked, and the activity of indole acetic acid oxidase (IAAO) decreased during the prophase of adventitious root formation in both the direct and indirect rooting, suggesting the positive regulation of POD and PPO and the negative regulation of IAAO during adventitious root initiation. Compared with those of indirect rooting, the relatively greater activities of POD and PPO and lower activity of IAAO were related to direct rooting and the number of adventitious roots. A total of 4265 proteins were identified from the base of the cuttings, of which 343, 236 and 37 proteins were highly expressed before treatment, in root primordia induction to adventitious root formation, and adventitious root elongation stages, respectively. Through hierarchical cluster analysis, 23 peroxidase and endogenous hormone regulatory proteins were screened and obtained; these included 10 peroxidases, 1 auxin regulatory protein, 3 ABA regulatory proteins, 2 jasmonic acid regulatory proteins, and 3 gibberellin regulatory proteins, which were highly expressed during the late cutting period. Finally, a hypothetical model of the regulatory network of the differential proteins involved in adventitious root formation in P. orientalis was constructed.

Though the leaves of Cinnamomum tamala is extensively employed in culinary applications due to its rich aroma and therapeutic properties, the produce exhibits variability in composition and contents of leaf essential oil due to fluctuations in climatic conditions and harvesting time. This work evaluated the impact of seasonal and diurnal variations on the composition and contents of aroma volatiles in the mature leaves of C. tamala. In summer, the profile of aroma volatile was dominated by phenylpropanoids (112.96 ± 24.11 μg/g of freeze-dried leaf tissue) while in winter monoterpenes (58.45 ± 8.194 μg/g of freeze-dried leaf tissue) acquired the dominance. The variability in the contents of primary metabolites was shown to be influenced by the harvesting season and time. Organic acids and sugars showed highest accumulation in leaves harvested during summer evening and winter morning, respectively. Histochemical study showed the presence of lipids and terpenes in the secretory cells as revealed through sudan III and NaDi staining. The ontogeny of secretory oil cells that accumulate essential oil were elucidated through ultrastructural study.

Unravelling the complexities of transpiration can be assisted by understanding the oxygen isotope composition of transpired water vapour (δE). It is often assumed that δE is at steady state, thereby mirroring the oxygen isotope composition of source water (δsource), but this assumption has never been tested at the whole-tree scale. This study utilized the unique infrastructure of 12 whole-tree chambers enclosing Eucalyptus parramattensis E.C.Hall trees to measure δE along with concurrent temperature and gas exchange data. Six chambers tracked ambient air temperature and six were exposed to an ambient +3 °C warming treatment. Day time means for δE were within 1.2‰ of δsource (-3.3‰) but varied considerably throughout the day. Our observations show that E. parramattensis trees are seldom transpiring at isotopic steady state over a diel period, but transpiration approaches source water isotopic composition over longer time periods.

Leaves, the primary carbon fixers in autotrophic plants, undergo a complex senescence process, which is critical for the redistribution of nutrients and supports ongoing growth and development. This natural aging phenomenon, often triggered at the end of a plant's life cycle or during the autumn season in perennial species, is finely regulated at multiple levels. Premature senescence can disrupt normal plant development, while the timing and pace of senescence significantly impact crop yield and quality. Notably, accelerated senescence under stress conditions may enhance the survival of future generations, suggesting an evolutionary strategy for plants to cope with harsh environments. Our review focuses on the molecular regulation of leaf senescence in woody plants, emphasizing the intricate determinants and regulatory mechanisms involved, including the role of phytohormones, environmental cues, and genetic factors. We highlight recent advances in understanding the regulation of leaf senescence in woody plants, integrating insights from multidisciplinary approaches and cutting-edge technologies.

Freeze-thaw cycles (FTCs) are the major seasonal environment stress in the temperate and boreal forests, inducing hydraulic dysfunction and limiting tree growth and distribution. There are two types of FTCs in the field: FTCs with increasing temperature from winter to spring (spring FTCs); and FTCs with decreasing temperature from autumn to winter (autumn FTCs). While previous studies have evaluated the hydraulic function during the growing season, its seasonal changes and how it adapts to different types of FTCs remain unverified. To fill this knowledge gap, the eight tree species from three wood types (ring- and diffuse-porous, tracheid) were selected in a temperate forest undergoing seasonal FTCs. We measured the branch hydraulic traits in spring, summer, autumn, and early, middle and late winter. Ring-porous trees always showed low native hydraulic conductance (Kbranch), and high percentage loss of maximum Kbranch (PLCB) and water potential that loss of 50% maximum Kbranch (P50B) in non-growing seasons (except summer). Kbranch decreased, and PLCB and P50B increased in diffuse-porous trees after several spring FTCs. In tracheid trees, Kbranch decreased after spring FTCs while the P50B did not change. All sampled trees gradually recovered their hydraulic functions from spring to summer. Kbranch, PLCB and P50B of diffuse-porous and tracheid trees were relatively constant after autumn FTCs, indicating almost no effect of autumn FTCs on hydraulic functions. These results suggested that hydraulic functions of temperate trees showed significant seasonal changes, and spring FTCs induced more hydraulic damage (except ring-porous trees) than autumn FTCs, which should be determined by the number of FTCs and trees' vitality before FTCs. These findings advance our understanding of seasonal changes in hydraulic functions and how they cope with different types of FTC in temperate forests.

Desert shrubs play a crucial role in controlling desertification and promoting revegetation, but drought often hinders their growth. Investigating the hydraulic strategies of desert shrubs is important in order to understand their drought adaptation and predict future dynamics under climate change. In this study, we measured the hydraulic-related characteristics of roots, stems and leaves in 19 desert shrub species from northern China. We aimed to explore the hydraulic coordination and segmentation between different plant organs. The results were as follows: (i) specific root length was positively correlated with the water potential inducing a 50% loss in stem hydraulic conductivity (P50stem) and negatively correlated with stem hydraulic safety margin. This suggested that water uptake efficiency of the fine roots was traded off with stem embolism resistance and hydraulic safety. (ii) The water potential inducing a 50% loss in leaf hydraulic conductance was significantly less negative than P50stem, and fine root turgor loss point was significantly less negative than P50stem, indicating a hydraulic segmentation between the main stem and terminal organs. (iii) The most negative leaf turgor loss point indicated that leaf wilting occurred after substantial leaf and stem embolism. The high desiccation resistance of the leaves may serve as an important physiological mechanism to increase carbon gain in a relatively brief growth period. In summary, this study elucidated the hydraulic strategies employed by desert shrubs from a whole-plant perspective.

Coating high concentrations of copper (Cu) on the inner wall of containers can efficiently inhibit root entanglement of container-grown seedlings. However, how the protective and defensive responses of roots maintain root structure and function during Cu-root pruning is still unclear. Here, Duranta erecta seedlings were planted in the containers coated with 40 (T1), 80 (T2), 100 (T3), 120 (T4), 140 (T5), and 160 (T6) g L-1 Cu(OH)2 with containers without Cu(OH)2 as the control. Although T5 and T6 produced the best inhibitory effect on root entanglement, root anatomy structure was damaged. T1 and T2 not only failed to completely control root circling, but also led to decreased root activity and stunted growth. Cu(OH)2 treatments significantly increased lignin concentration of roots with the highest values at T3 and T4. Compared with T3, seedlings at T4 had higher height, biomass, and root activity and no significant root entanglement. Excessive Cu accumulation in Cu(OH)2 treatments changed the absorption of other mineral nutrients and their allocation in the roots, stems, and leaves. Overall, Ca was decreased while Mg, Mn, Fe, and K were increased, especially K and Mn at T4 which is related to defense capacity. The results indicate that there is a Cu threshold to balance root entanglement control, defense capacity, and nutrient uptake function under excessive Cu for container-grown D. erecta seedlings.

Centrifuges provide a fast approach to quantify embolism resistance of xylem in vulnerability curves (VCs). Since embolism formation is assumingly driven by pressure only, spin time is not standardised for flow centrifuge experiments. Here, we explore to what extent embolism resistance could be spin-time dependent, and hypothesise that changes in hydraulic conductivity (Kh) would shift VCs towards higher water potential (Ψ) values over time. We quantified time-based shifts in flow-centrifuge VCs and their parameter estimations for six angiosperm species by measuring Kh over 15 minutes of spinning at a particular speed, before a higher speed was applied to the same sample. We compared various VCs per sample based on cumulative spin time, and modelled the relationship between Kh, Ψ, and spin-time. Time-based changes of Kh showed considerable increases and decreases at low and high centrifuge speeds, respectively, which generally shifted VCs towards more positive Ψ values. Values corresponding to 50% loss of hydraulic conductivity (P50) became less negative by up to 0.72 MPa in Acer pseudoplatanus, and on average by 8.5% for all six species compared to VCs that did not consider spin-time. By employing an asymptotic exponential model, we estimated time-stable Kh, which improved the statistical significance of VCs in 5 of the 6 species studied. This model also revealed the instability of VCs at short spin times with embolism formation in flow-centrifuges following a saturating exponential growth curve. Although pressure remains the major determinant of embolism formation, spin-time should be considered in flow-centrifuge VCs because not considering the time-dependent stability of Kh overestimates embolism resistance. This spin-time artefact is species-specific, and likely based on relatively slow gas diffusion that is associated with embolism propagation. The accuracy of VCs is improved by determining time-stable Kh values for each centrifuge speed, without considerably extending the experimental time to construct VCs.

Sugar maples (Acer saccharum Marshall) develop elevated stem pressures in springtime through the compression and expansion of gas bubbles present within xylem fibres. The stability of this gas within the fibres is hypothesised to be due to the elevated sugar concentration of maple sap and the presence of an osmotic barrier between fibres and vessels. Without this osmotic barrier gas bubbles are predicted to dissolve rapidly. In this work we investigated the existence of this osmotic barrier. We quantified the fraction of the xylem occupied by gas-filled fibres using synchrotron based microCT. After imaging fresh stem segments we perfused them with either a 2% sucrose solution or water, imaging again following perfusion. In this way we directly observed how total gas present in the fibres changed when an osmotic pressure difference should be present, with the 2% sucrose solution, and when it is absent, with the water. Following a first round of perfusion we perfused stem segments with the other perfusate, repeating this multiple times to observe how switching perfusates affected gas-filled fibres. We found that perfusing stem segments with water resulted in a significant reduction in the xylem fibre gas, but perfusing stem segments with a sucrose solution did not significantly reduce the gas in the fibres. These results support the hypothesis that an osmotic barrier exists between fibres and vessels.

Understanding how canopy-scale photosynthesis responds to temperature is of paramount importance for realistic prediction of the likely impact of climate change on forest growth. The effects of temperature on leaf-scale photosynthesis have been extensively documented but data demonstrating the temperature response of canopy-scale photosynthesis are relatively rare, and the mechanisms that determine the response are not well quantified. Here, we compared leaf- and canopy-scale photosynthesis responses to temperature measured in a whole-tree chamber experiment and tested mechanisms that could explain the difference between leaf and crown scale temperature optima for photosynthesis. We hypothesised that 1) there is a large contribution of non-light saturated leaves to total crown photosynthesis; 2) photosynthetic component processes vary vertically through the canopy following the gradient in incident light; and 3) seasonal temperature acclimation of photosynthetic biochemistry has a significant role in determining the overall temperature response of canopy photosynthesis. We tested these hypotheses using three models of canopy radiation interception and photosynthesis parameterized with leaf-level physiological data and estimates of canopy leaf area. Our results identified the influence of non-light saturated leaves as a key determinant of the lower temperature optimum of canopy photosynthesis, which reduced the temperature optimum of canopy photosynthesis by 6-8 °C compared to the leaf scale. Further, we demonstrate the importance of accounting for within-canopy variation and seasonal temperature acclimation of photosynthetic biochemistry in determining the magnitude of canopy photosynthesis. Overall, our study identifies key processes that need to be incorporated in terrestrial biosphere models to accurately predict temperature responses of whole-tree photosynthesis.

Intra-annual variations of carbon stable isotope ratios (δ13C) in different tree compartments could represent valuable indicators of plant carbon source-sink dynamics, at weekly time scale. Despite this significance, the absence of a methodological framework for tracking δ13C values in tree rings persists due to the complexity of tree ring development. To fulfill this knowledge gap, we developed a method to monitor weekly variability of δ13C in the cambium-xylem continuum of black spruce species [Picea mariana (Mill.) BSP.] during the growing season. We collected and isolated the weekly incremental growth of the cambial region and the developing tree ring from five mature spruce trees over three consecutive growing seasons (2019-2021) in Simoncouche and two growing seasons (2020-2021) in Bernatchez, both located in the boreal forest of Quebec, Canada. Our method allowed for the creation of intra-annual δ13C series for both the growing cambium (δ13Ccam) and developing xylem cellulose (δ13Cxc) in these two sites. Strong positive correlations were observed between δ13Ccam and δ13Cxc series in almost all study years. These findings suggest that a constant supply of fresh assimilates to the cambium-xylem continuum may be the dominant process feeding secondary growth in the two study sites. On the other hand, rates of carbon isotopic fractionation appeared to be poorly affected by climate variability, at an inter- weekly time scale. Hence, increasing δ13Ccam and δ13Cxc trends highlighted here possibly indicate shifts in carbon allocation strategies, likely fostering frost resistance and reducing water uptake in the late growth season. Additionally, these trends may be related to the black spruce trees' responses to the seasonal decrease in photosynthetically active radiation. Our findings provide new insights into the seasonal carbon dynamics and growth constraints of black spruce in boreal forest ecosystems, offering a novel methodological approach for studying carbon allocation at fine temporal scales.

None declared.Conflict of interestPlantation of Chinese fir, a popular woody tree species, faces sustainable issues such as nutrient deficiency and increasing disease threat. Rhizosphere and endophytic bacteria play important roles in plant' nutrient absorption and stress alleviation. Our understanding on the microbiome structure and functions are proceeding rapidly in model plants and some crop species. Yet, the spatial distribution and functional patterns of the bacteriome for the woody trees remain largely unexplored. In this study, we collected rhizosphere soil, non-rhizosphere soil, fine root, thick root and primary root samples of Chinese fir, and investigated the structure and distribution of bacteriome, as well as the beneficial effects of endophytic bacterial isolates. We discovered that Burkholderia and Paraburkholderia genera were overwhelmingly enriched in rhizosphere soil and the abundance of Pseudomonas genus was significantly enhanced in fine root. By isolating and testing the nutrient absorption and pathogen antagonism functions of representative endophytic bacteria species in Pseudomonas and Burkholderia, we noticed that P-solubilising functional isolates was enriched in fine root, while pathogen antagonism isolates was enriched in thick root. As a conclusion, our study revealed that the endophytic and rhizosphere environments of Chinese fir hold distinct structure and abundance of bacteriome, with potential specific functional enrichment of some bacterial clades. These findings assist us to further study the potential regulation mechanism of endophytic functional bacteria by the host tree, which will contribute to beneficial microbe application in forestry plantation and sustainable development.