Tree physiology最新文献

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 that have been demonstrated to be affected or unaffected by chloroplast redox/energy state. According to the former hypothesis alone, we modeled 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.

Considerable attention has been paid to addressing methodological concerns related to measurements of embolism in conduits of angiosperm xylem. A fast, easy and cheap method is based on gas extraction measurements from dehydrating samples to obtain pneumatic vulnerability curves (VCs). Here, we tested the assumption that cutting open conduits leads to gas-filled lumina when these are cut in air at fairly high water potentials, which is required to detect embolism in intact conduits. We performed VCs with the Pneumatron for 12 angiosperm species and extracted sap from cut-open vessels in branches of nine species under early stages of branch dehydration. The optical method was applied to Citrus plants as an alternative reference method to estimate embolism resistance. We found an increase in gas discharge during early stages of dehydration, which affected the pneumatic VCs for most of the species studied. Xylem sap residue was not absorbed immediately by surrounding tissue in cut-open conduits in six of the nine species but gradually disappeared over time during progressive dehydration. The amount of gas discharged increased until all residual sap was absorbed, and was not related to embolism. We conclude that residual xylem sap in cut-open conduits affects early stages of pneumatic VCs and represents a novel artifact that can easily be corrected for. Yet, it remains unclear why exactly the air-water meniscus in cut-open conduits did not fully withdraw to the conduit end wall in most species. By analyzing the slope of VCs over time, we could improve estimations of embolism resistance, as evidenced by a strong agreement between the pneumatic and the optical methods. Since residual sap in cut-open conduits of some species could slightly underestimate embolism resistance, we propose to apply a correction for this artifact based on the high time-resolution measurements taken with a Pneumatron.

Plants have developed intricate mechanisms to adapt to fluctuating nitrogen availability in the soil, including modulation of anthocyanin biosynthesis. However, the regulation mechanism of lateral organ boundary domain (LBD) transcription factors on anthocyanin biosynthesis under low nitrogen conditions remains poorly understood. Here, we functionally characterized PsLBD42 from Populus simonii, a class II LBD transcription factor, which was upregulated under low nitrogen conditions. PsLBD42-overexpression transgenic poplar exhibited enhanced resistance to the low nitrogen stress with increased photosynthetic rates and decreased photooxidation, but unchanged nitrogen content and uptake capability. Meanwhile, the accumulation of anthocyanin related with photooxidation was significantly increased in the leaves of PsLBD42-overexpression transgenic poplar. The contrary results were showed in the lines of PsLBD42-suppression transgenic poplar. It was confirmed that PsLBD42 could directly binds to the promoters of PsUGT78D2 and PsUGT79B3 in the genes of anthocyanin pathway by yeast one-hybrid, dual luciferase, and ChIP-qPCR assays. Under low nitrogen conditions, the overexpressing PsUGT78D2 and PsUGT79B3 in the poplar leaves accumulated more anthocyanins while the suppression of PsUGT78D2 and PsUGT79B3 reduced anthocyanins content. Furthermore, overexpression of PsUGT78D2 and PsUGT79B3 restored anthocyanin levels in PsLBD42-RNAi lines under low nitrogen conditions. Collectively, our results indicate that the PsLBD42-PsUGT78D2/PsUGT79B3 module regulates anthocyanin accumulation in poplar leaves as a novel mechanism to enhance poplar tolerance to low nitrogen stress.

Drought and herbivory are prevalent stressors that often interact to constrain forest regeneration. Drought-induced depletion of nonstructural carbohydrates (NSC) may impair seedling chemical defenses, increasing vulnerability to pests and pathogens. To investigate NSC thresholds influencing defense capacity, we quantified the effects of drought and simulated insect herbivory on NSC (starch, sucrose, glucose, and fructose) and mono- and sesquiterpene (MST) defenses in five-year-old piñon pine (Pinus edulis) seedlings. Seedlings were either well-watered or subjected to drought until stomatal closure before treatment with methyl jasmonate (MeJA) to simulate herbivory. Both drought and MeJA treatments individually reduced NSC content in needles and stems by 50%, with no further decrease observed under combined stressors. Regardless of stressor(s), NSC was depleted to ~0.5% and ~0.7% dry weight in needles and stems, respectively. While drought alone more than doubled MST concentrations in both tissues, total MST concentrations remained unchanged in response to MeJA, suggesting NSC was instead mobilized to support other unidentified metabolic processes. By demonstrating that NSC were depleted to similar lower limits across all stressors and combinations, this study suggests the existence of reserve thresholds below which seedling capacity to respond to subsequent stress may become constrained.

Water and nutrient limitation typically co-occur in terrestrial ecosystems, exerting complex interactions on plants. However, the nature of these interactions on fine roots remains poorly understood. Here, we conducted a full-factorial experiment manipulating water and nutrient stress using seedlings of four tree species, focusing on the individual and interactive effects of drought (D) and nutrient stress (N) on fine roots. We found that both drought and nutrient stress induced a shift toward resource-acquisitive strategies in root traits, yet the magnitude of root responses differed between the two stressors. Specifically, nutrient stress exerted the strongest effects on root morphological traits, whereas the two stressors had relatively comparable impacts on root nutrient content. Under combined stress, this acquisitive shift was modulated, exhibiting a trend toward resource conservation. The interactive effects of D×N were highly trait-specific: additive effects dominated the responses of root morphological traits, whereas antagonistic effects were more prevalent in root nutrient content traits. Moreover, these interactions varied with treatment intensity and root order rather than with interspecific variation. Specifically, the antagonistic effect of D×N became stronger with increasing drought and nutrient stress intensity, as well as with ascending root order. Overall, this study provides critical insights into root adaptation strategies under complex environmental change, offering an empirical basis for refining predictive models and guiding the design of more ecologically relevant multi-factor experiments.

Quercus glauca (Q. glauca) is an ecologically and economically important evergreen broadleaf species in subtropical Asia, yet its productivity is increasingly threatened by drought stress. Brassinosteroids (BRs), a class of plant steroidal hormones, play crucial roles in stress adaptation. In this study, we used an integrated multi-omics approach to investigate how exogenous BR application enhances drought resistance in Q. glauca. Physiological analyses showed that BR reduced oxidative damage by lowering ROS and MDA levels, while increasing antioxidant enzyme activities (SOD, POD, CAT) and osmoprotectants (proline, soluble sugars). Anatomical observations indicated BR preserved mesophyll structure and stomatal aperture. Transcriptomic analysis revealed that BR not only restored gene expression to the pre-stress state but also induced a new transcriptional program distinct from both CK and drought that was enriched in MAPK signaling, hormone crosstalk, and carbohydrate metabolism. Metabolomics confirmed the accumulation of protective metabolites (flavonoids, sterols, osmolytes) and strategic reallocation away from energy-costly secondary metabolism. Weighted Gene Co-expression Network Analysis identified hub genes (AKR2, ERF020-like, At4g00960-like) linking BR-responsive expression patterns to drought-mitigating traits. Collectively, these results support a multi-phase model in which BR orchestrates detoxification, metabolic rewiring, structural repair, and sustained signal perception. This study provides novel insights into BR-mediated drought resilience in Q. glauca and identifies molecular targets for silvicultural stress management.

Traditional cultivation of medicinal Cyclocarya paliurus has consistently failed to resolve the growth-secondary metabolism trade-off, affecting yield and quality. Utilizing dark septate endophyte, which induces host plant endogenous hormone synthesis and enhances stress resistance, offers a feasible and effective method to balance this trade-off relationship. In this study, sterile C. paliurus seedlings were subjected to dark septate endophyte inoculation, jasmonic acid (JA) spraying and JA inhibitor treatments. We demonstrated that dark septate endophyte inoculation increased seedling height by 59.46% and biomass by 15.94%. This treatment established an antioxidant barrier in plants, maintained reactive oxygen species homeostasis and alleviated membrane lipid peroxidation, thereby boosting plant stress resistance. ITS gene sequencing confirmed that dark septate endophyte enhanced root fungal diversity. Integrated multi-omics analysis revealed that dark septate endophyte promoted flavonoid biosynthesis (total flavonoids increased by 15.30%) through triggering the JA signaling pathway to activate MYC2-mediator complex subunit 25, significantly increasing vitexin content. Our results identify dark septate endophyte as a pivotal metabolic checkpoint for synergistically enhancing medicinal plant yield and quality. This study provides novel insights into eco-efficient cultivation strategies and lays the foundation for the broader application of beneficial dark septate endophyte in agroforestry practices.

Rainfall pulses create brief but critical opportunities for carbon uptake in seasonally dry forests; however, how tree seedlings recover photosynthetic function during the establishment phase following these short-lived rewetting events under field conditions remains poorly understood. In particular, the coordination and timing of hydraulic, stomatal and biochemical recovery processes during natural rainfall pulse-dry-down cycles are not well quantified, despite their importance for carbon-water coupling and drought resilience. Here, we investigated short-term physiological responses of establishing Eucalyptus seedlings during naturally occurring rainfall pulse-dry-down cycles. We measured leaf water potential (Ψleaf), gas exchange and photosynthetic capacity (Vcmax, Jmax) before and after rainfall to assess recovery dynamics of diffusional and biochemical processes under contrasting atmospheric demand. Across species, Ψleaf and stomatal conductance improved rapidly following rainfall, reflecting transient hydraulic relief, while net photosynthesis increased by 40-60% within 1-3 days. In contrast, biochemical capacity responded more gradually: Vcmax declined by up to ~ 15% and Jmax by 20-40% during dry-down and showed limited or partial recovery after rewetting. Limitation partitioning revealed asynchronous recovery, with stomatal limitation relaxing rapidly after rainfall under low vapour pressure deficit (VPD), whereas under high VPD, biochemical recovery preceded full stomatal reopening. The xeric-origin Eucalyptus cladocalyx sustained assimilation at more negative Ψleaf and exhibited greater biochemical stability, whereas intermediate and mesic species (E. grandis, E. urophylla, E. cloeziana) showed rapid but short-lived post-rain responses. Together, these results demonstrate that photosynthetic recovery during the seedling phase is asynchronous and strongly modulated by atmospheric demand, shaping short-term carbon-water coupling under increasingly pulsed hydroclimates.

Casuarina equisetifolia L., a key pioneer species in tropical and subtropical coastal shelterbelts, suffers from ecological decline owing to recurrent infestations by Lymantria xylina Swinhoe. To address this, we deciphered the molecular defence mechanisms and identified reliable biomarker metabolites for resistance breeding. Phenotypic analyses suggesting that the resistance to L. xylina was jointly mediated by antixenosis and antibiosis, and three resistant half-sib families (e.g., 3-52, 5-80 and 5-218) were preliminarily identified. Integrated transcriptomic and metabolomic profiling of L. xylina herbivory demonstrated significant enrichment of differentially expressed genes in the circadian rhythm-plant, jasmonic acid signaling and phenylpropanoid biosynthesis pathways-which may mediate the optimization of defence responses. In parallel, differential accumulation metabolites were predominantly enriched in α-linolenic acid metabolism. In particular, the content of α-linolenic acid strongly correlated with resistance, while flavonoids and tannins also exhibited significant positive correlations, confirming their roles in the defence response. These results suggest that the α-linolenic acid to phenylpropanoid cascade may function as a core defence axis in C. equisetifolia against L. xylina. Collectively, α-linolenic acid, flavonoids and tannins serve as candidate biomarkers for breeding insect-resistant C. equisetifolia genotypes.