Tree physiology最新文献

Constrained carbon allocation toward secondary metabolites involved in chemical defense is a common explanation for widespread drought-related beetle-kill in conifers-we challenge the generality of this explanation. While monitoring drought stress (ψpd), we tracked both carbon reserves (non-structural carbohydrates) and chemical defenses (terpenes, phenolics, resin flow) in mature Pinus edulis Englem. trees experiencing either short-term (3-year) or a 'legacy' long-term (13-year) throughfall exclusion treatments, plus a control. We also quantified the Δ14C-age of resin to measure past allocation to current defense. While 72% of trees in short-term throughfall exclusion plots died (attacked by bark beetles, Ips confusus LeConte), mortality patterns were unrelated to throughfall exclusion intensity and all 'legacy' trees survived. We thus assessed trees in four survivorship categories: control, 'legacy', surviving, and dying trees. We found concentrations of certain defense compounds (leaf phenolics, twig monoterpenes) increased with drought stress, particularly in dying trees. In the main stem, dying trees exhibited similar terpene concentrations (94%) and phenolic concentrations (139%) relative to control trees. Compared with control trees, only 'legacy' trees had reduced stem terpenes (-49%, P < 0.05) after a decade of drought. Δ14C-age of resin could be up to 10.2 ± 0.5 years old, where the oldest resin was exuded from trees with low sugar concentrations and more negative Ψpd. Our results suggest that drought imposes a weak constraint on carbon allocation to resin-based defense. Instead, we primarily found evidence of increased concentrations of terpene and phenolic compounds under drought, even in dying trees, and only observed reductions in resin-based defenses after 10+ years of drought. Δ14C-ages demonstrate limited resin turnover and/or synthesis of resin from old reserves, suggesting that long-term drought is required to reduce resin-based defenses. Persistent allocation coupled with past investments appears to preserve or enhance concentrations of resin-based defenses even under lethal drought stress in P. edulis.

Priestia sp. B6 (strain B6) enhances lead (Pb) translocation from the roots to the aerial parts in Salix integra, nearly doubling its Pb translocation capacity. This study aims to elucidate the mechanism by which strain B6 facilitates Pb entry into the root xylem via the apoplastic pathway. Priestia sp. Strain B6 was capable of colonizing the roots, branches and leaves of S. integra. It migrated from the roots to the branches via the xylem, and subsequently moved to the epidermis of the branches and leaves through intercellular spaces. The deposition sites of strain B6 and Pb were primarily located in the cell walls and intercellular spaces. Inoculation with strain B6 resulted in a maximum 70.22% increase in Pb concentrations in the root cell walls, and this was associated with reduced pectin methylesterase activity and enhanced the number and migration activity of functional groups. Additionally, Pb desorption capacity was increased, allowing Pb to re-enter the intercellular spaces. In addition, abscisic acid and gibberellin A3 concentrations, and phenylalanine ammonia-lyase activity were reduced by 40.48%, 52.78% and 62.23%, respectively. Consequently, the Casparian strip formed further from the root tip, and both the Casparian strip and suberin lamellae developed incompletely, which facilitated Pb entry into the root xylem via the apoplastic pathway. Simultaneously, the Pb detoxification capacity of S. integra was enhanced by reducing the H2O2, OH- and increasing the concentrations of chelating agents glutathione and metallothionein, as well as the activities of superoxide dismutase and peroxidase. These findings indicate that strain B6 enhances Pb translocation through the apoplastic pathway while promoting Pb detoxification in the roots of S. integra.

Iron plaque, a phenomenon widely found in wetland plants, is an accumulation of metal (hydr)oxides precipitated on root surfaces primarily driven by rhizosphere oxidation. However, the potential function of iron plaque on plant hypoxia tolerance is largely ignored. Thus, the effects of iron plaque on root O2 dynamics and respiratory metabolism were investigated using the seedlings of Aegiceras corniculatum. O2 microelectrodes were applied to determine partial pressure of oxygen (pO2) within roots, while respiratory metabolism was analyzed using enzyme activity assay kits, transcriptomics and real-time quantitative PCR (qRT-PCR). Visible reddish plaques were observed on the roots of field-collected A. corniculatum seedlings, forming a coating that appeared to penetrate the intercellular spaces of the outer one to two cell layers. The data further revealed a significant role of iron plaque in elevating pO2 within roots, which can mitigate hypoxic inhibition and benefit plant performance under hypoxic stresses. Compared with non-plaque roots, roots with iron plaque exhibited significantly higher adenosine triphosphate (ATP), elevated tricarboxylic acid (TCA) respiration rates, and upregulated TCA cycle-associated enzymes and genes. Besides, suppressed anaerobic fermentation-associated byproducts (e.g., ethanol) and enzymes/genes (e.g., alcohol dehydrogenase and its encoding gene AcADH1) were simultaneously observed in the roots with iron plaque due to enhanced root internal pO2. Suppressed glycolysis pathway was also observed in the roots with iron plaque, indicating less consumption of carbon resources under hypoxic stresses. In conclusion, this study provided evidence for an interesting link between iron plaque and increased O2 retention within roots, which improved the efficiency of ATP yield through respiratory metabolism.

Plants deploy complex transcriptional responses to herbivores yet differences in the responses to generalist versus specialist insects, especially in long-lived tree species, are still poorly understood. Here, we analysed the transcriptional responses in Quercus robur L. leaves to infestation by two chewing insect species: the specialist moth Tortrix viridana L. and the generalist moth Lymantria dispar L. Regardless of insect species, we observed extensive gene induction. Key regulators such as the transcription factors MYC2, JAZ and ERF1, primarily activate defence gene expression via jasmonate and ethylene pathways after feeding by the generalist or the specialist. A total of 1591 genes were differentially expressed between the two herbivore treatments. Feeding by L. dispar triggered a broader transcriptional response, stronger activating pathways related to jasmonate, abscisic acid, auxin and ethylene signalling, as well as genes involved in terpene synthesis, monooxygenase activity and phloem development. In contrast, T. viridana induced a more specialized profile, including genes associated with serine-type endopeptidase activity, cell wall and cell wall organization, such as those encoding hydroxyproline-rich glycoproteins or pectin esterase inhibitors. This suggests a role of cell wall-related defences in response to specialist herbivores. Network analysis of Arabidopsis thaliana (L.) Heynh. homologues highlighted MYC2 as a central regulatory hub in both responses. Activation of MYC2 triggers downstream responses, including the induction of secondary metabolism genes, e.g., QrTPS1 encoding a functional sesquiterpene synthase, with germacrene D as its primary product. Transcriptional differences between resistant and susceptible oak genotypes were more pronounced following specialist than generalist herbivore feeding. These results provide insights into genome-scale herbivore-specific and genotype-mediated defence programmes at the transcriptome level and highlight promising gene targets for future functional genomics and natural variation studies in a keystone forest tree.

Convergence in strategies and traits that minimise drought damage and promote recovery have been shown to explain favourable drought responses in trees (Choat et al. 2012). Conversely, diversity and variation, in many ways, underpin biological resilience. Biodiversity can be a marker of ecosystem resilience, particularly in the face of climate extremes (Isbell et al. 2015) and diversity in hydraulic traits has been shown to increase forest resilience to drought (Anderegg et al. 2018). Additionally, high variation in traits, even within individual trees, has been linked to species' drought survival and recovery (Rodriguez-Dominguez et al. 2018, Cardoso et al. 2020, Johnson et al. 2022). Skelton et al. (2025) use six tree species from a South-African plant community to assess the power of commonly measured traits and metrics to predict drought responses. They also assess whether there is evidence for species convergence around strategies that promote drought survival and recovery. A natural drought during the experiment provided the ideal opportunity to test whether measured and calculated markers for drought resistance can accurately predict the extent of damage and recovery in the trees residing in this unique drought-prone biome.

The effect of ectomycorrhizal (ECM) fungi on the absorption and transport of heavy metals by host plants remains elusive. We experimentally assessed rapid cadmium (Cd) diffusion by two species of Suillus mycelium. Furthermore, we evaluated Cd absorption by ECM Pinus thunbergii Parl. and used transcriptomics to study the gene expression of P. thunbergii under Cd stress. In vitro experiments revealed that Cd2+ was transported through the apoplastic space more rapidly than through the mycelial symplast. The net Cd2+ influx rates in epitaxial hyphae were the highest, followed by those in the mantle of P. thunbergii inoculated with Suillus, whereas the lowest influx rate was found in the ECM-free fine root portions. Under Cd stress, the expression levels of PtZnTs, PtZIPs and PtHMA2 in ECM P. thunbergii roots were significantly higher than those in non-mycorrhized P. thunbergii. The assessment of Cd distribution in P. thunbergii revealed that Cd was transported to the needles of ECM P. thunbergii after 48 h; however, it was not detected in non-mycorrhized P. thunbergii. The essential element Cu exhibited similar results as the non-essential element Cd. Furthermore, two species ECM fungi Suillus accelerates the uptake and transport of Cd in the host plant P. thunbergii.

The xylem and phloem anatomy of co-existing tree species provides valuable information on how different tree species face climate change and adjust their vascular structure to local weather conditions. We examined and compared annual ring widths and conduit size in earlywood and early phloem in Fraxinus ornus, Quercus pubescens and Ostrya carpinifolia in a sub-Mediterranean site during the period 2019-2021. The selected xylem and phloem traits were correlated with monthly weather conditions (precipitation and temperature). We found that phloem increment widths and conduits in earlywood and early phloem in the studied tree species showed different trends in terms of interannual variability and in relation to local weather conditions. In F. ornus, May conditions affected xylem traits, while June conditions phloem traits. In Q. pubescens, winter and March precipitation was related to phloem development. In O. carpinifolia, xylem ring width was positively correlated with June precipitation, while early phloem conduits were negatively affected by April temperature. Only two consistent patterns were detected across the species and years studied: wider xylem increments compared with phloem increments, and wider earlywood vessels compared with early phloem sieve tubes. Statistically significant differences were observed among species across all years for the size of xylem and phloem conduits and the hydraulic conductivity of earlywood vessels, which indicates great differences in the calculated hydraulic conductivity among the tree species. To summarize, hydraulic conductivity of earlywood vessels in Q. pubescens was on average for all 3 years 10.4-times and 114-times larger than in F. ornus and O. carpinifolia, respectively. High interannual variability and species-specific sensitivity of xylem and phloem traits to precipitation and temperature confirm high plasticity and different radial growth strategies of the studied tree species to ensure optimal functioning under local weather conditions.

Stable isotopes of carbon, oxygen and hydrogen in tree rings provide a record of plant physiological processes and environmental variability. Although an increasing number of studies now apply triple-isotope approaches, no investigation has yet tested their temporal stability over millennial timescales or assessed the relative impacts of physiology versus climate on long-term isotopic signals. Here, we used 9000 years of multi-isotope records from co-occurring deciduous larch (Larix decidua) and evergreen cembra pine (Pinus cembra) at the Alpine treeline. We found a high interspecies coherence for δ18O throughout the Holocene with a robust summer hydroclimate sensitivity, confirming its dominance by environmental drivers. In contrast, δ13C and δ2H show weaker and less stable coherence, reflecting species-specific physiology. Larch exhibits tight δ2H-δ18O and δ2H-δ13C correlations and stronger climate sensitivity, consistent with its reliance on freshly assimilated carbon. Pine, by contrast, shows weaker δ2H-climate relationships and frequent decoupling from δ13C and δ18O, reflecting potential storage use and metabolic fractionations. Thus, inter-isotope relationships reveal that δ18O is a robust long-term climate proxy, while δ13C and δ2H encode contrasting carbon-use strategies and metabolic processes across species that may vary over time. Together, these findings demonstrate that multi-isotope, multi-species approaches not only strengthen climate reconstructions but also provide a physiological dimension to long-term isotope records.

Manganese (Mn), a critical component of the photosystem II oxygen-evolving complex, chlorophyll biosynthesis pathway and antioxidant systems, manifests functional mechanisms that remain inadequately elucidated in the context of arbuscular mycorrhizal fungi (AMF)-mediated plant tolerance to water deficit (WD). This study examined how Funneliformis mosseae (T.H. Nicolson & Gerd.) C. Walker & A. Schüßler inoculation enhances WD (55% maximum of the maximum field water capacity for 10 weeks) tolerance in trifoliate orange (Poncirus trifoliata) by modulating Mn chemical forms and key physiological processes. AMF inoculation significantly improved various growth parameters irrespective of soil moisture. AMF inoculation significantly enhanced photosynthetic efficiency, various chlorophyll levels and photosystem stability under WD. In leaves, AMF inoculation significantly increased levels of inorganic, bound and residual Mn fractions under varying moisture conditions, while concurrently reducing oxalate-bound Mn, in addition to an increase in phosphate Mn under WD. AMF colonization upregulated the expression of PtHEMG1 and PtMnSOD under WD, and also modulated the expression of P. trifoliata metal tolerance proteins (PtMTPs), as evidenced by the enhancement of specific PtMTP members (PtMTP4/5/7/9) under normal watered and the suppression of PtMTP3/9 under WD. Correlation analysis demonstrated coordinated regulation among photosynthetic efficiency, Mn levels, PtMTPs and PtHEMG1. In conclusion, the AMF-induced shift in Mn chemical forms (e.g. pectate-/protein-bound Mn) coordinated with enhanced chlorophyll biosynthesis and photosynthetic performance in trifoliate orange plants under WD.