Populus trees are commonly used in constructing shelter forests in water-limited areas of China; however, different poplar species are facing various levels of dieback risks under the increased drought associated with climate change. The objective of this study was to explore whether crown height affects the xylem hydraulics and to evaluate the suitability of different Populus species for constructing sustainable shelterbelt in water-limited regions. Xylem hydraulics and water relations of branches at upper and lower positions of tree crown, alongside radial growth rate, were compared between two species that are commonly used in shelterbelt construction but have contrasting crown types, i.e., Populus simonii with short oval crowns and Populus pioner with tall columnar crowns. The results showed that as height increases, P. simonii exhibited enhanced hydraulic efficiency and safety, while no significant differences in these hydraulic traits across canopy layers were observed in P. pioner. In addition, the upper branches of P. pioner have lower water potential and longer water flow paths, resulting in lower hydraulic safety margin, which means that the species was more prone to hydraulic limitation and eventually dieback. Adjustments of vessel sizes and leaf mass per area along the crown of P. simonii contributed to the increase in xylem hydraulic capacity in upper branches and the homeostasis of leaf water potential within the crown. Although the adjustment of using water more conservatively potentially compromised the whole-tree carbon assimilation and thus growth rate, P. simonii seemingly showed stronger adaptability to projected drought intensification by shedding part of branches at the crown bottom and might thus be a more suitable species for establishing stable shelterbelt in water-limited areas. This study, from perspectives of tree physiology, provides an important reference for afforestation species optimization and thus the sustainable management of shelterbelts in water-limited areas of northern China.

Plantations are an important component of global forest coverage, but their performance is increasingly affected by water limitation due to climate change. Employing a rainfall exclusion facility, we report on the impacts of reduced rainfall on leaf water relations and organ morphological traits, in six Populus varieties commonly used for afforestation across North China. We exposed trees to 2 years of 50% rainfall exclusion and found that leaf hydraulic traits conferring drought resistance, including water potential thresholds triggering xylem embolism, leaf pressure-volume characteristics and metrics quantifying the risk of hydraulic dysfunction (i.e., hydraulic safety margin), were not improved, despite slightly but significantly decreased predawn leaf water potential and growth rate. Interspecific variation in response to rainfall exclusion was observed for some morphological traits, yet the adjustments were unlikely to benefit drought resistance. Overall, our results demonstrate an overall lack of physiological adaptive adjustments for leaves in response to rainfall reduction at early growth stage for these trees. If this response persists as trees age, the function of these trees will be potentially reduced due to increased risk of hydraulic failure, if the drying trend continues in their planting region.

Although the presence of methanogens in living tree trunks was reported more than 50 years ago, it has recently been suggested that trees in upland forests constitute a net sink for atmospheric CH4, which contradicts other recent or older studies. To clarify the role of tree trunks as net emitters or consumers of CH4, we measured trunk CH4 fluxes of 11 upland species, up to 12 m above ground for some trees, and estimated their ex-situ potential CH4 oxidation capacity. Trees from seven species emitted CH4 from their trunks, some at height well-above 2 m above ground, whereas little CH4 was emitted from the trunks of the other four species. The average rate of CH4 oxidation was an order of magnitude lower than the average trunk CH4 fluxes measured on the same individuals, consistent with the very weak net uptake of CH4 occasionally measured on some trees. CH4 oxidation in the bark could nevertheless mitigate CH4 emissions from tree trunks. Trees in our mountain forest were likely a net source of CH4 to the atmosphere rather than a net sink of atmospheric methane, suggesting that it is premature to conclude that tree surfaces could be a significant sink for atmospheric CH4 globally.

Accelerated drought stress along with global warming has significantly impacted high-elevation ecosystems, causing a massive decline of conifers worldwide, including Korean fir (Abies koreana E.H.Wilson). However, studies on the climate adaptability and underlying physiological mechanisms of coexisting species remain limited, despite their importance for understanding future species composition. To investigate species-specific responses to climate change, a rainfall reduction and heat experiment was implemented by blocking precipitation by 33% and 67% and increasing temperature by 1.5°C for three coexisting high-elevation tree species: Korean fir, Korean pine (Pinus koraiensis Siebold & Zucc.), and Manchurian ash (Fraxinus mandshurica Rupr.). Korean fir exhibited the most sensitive stomatal control to conserve its hydraulic status, which significantly suppressed photosynthesis, depleted root starch reserves, and ultimately reduced growth. In contrast, Manchurian ash showed the highest resistance, with stable stomatal response through active leaf osmoregulation and increased chlorophyll content, which supported the maintenance of photosynthesis and root nonstructural carbohydrate (NSC) reserves. Korean pine exhibited intermediate responses, with the second-most sensitive stomatal and photosynthetic regulation, along with temporarily tolerant traits such as increased leaf sugar and chlorophyll content, while allocating relatively more carbon to growth than to storage. This resulted in the highest mortality in Korean fir, followed by Korean pine and Manchurian ash. This study enhances our understanding of the early stress responses of high-elevation species and provides insights into predicting future forest dynamics.

Woody plants have garnered significant attention in recent years for their essential ecological and economic contributions. Protoplasts, isolated from plant cells, exhibited remarkable totipotency and offered immense potential in a broad array of biological and biotechnological fields. These included, but were not limited to, protein gene expression regulation, functional gene analysis, subcellular localization, interaction studies, gene editing, and single-cell sequencing. This review offered a comprehensive overview of protoplast isolation methods, key influencing factors, purification techniques, and viability assessment. It further explored the use of protoplast transient expression systems for gene function characterization, while highlighting the diverse applications of protoplast-based technologies, such as fusion, regeneration, genome editing, and single-cell sequencing. With technological advancements, future breakthroughs in these areas will be poised to create new avenues for research, genetic improvement, and biotechnological innovations in woody plants.

Fine root carbon (C), nitrogen (N), and phosphorus (P) stoichiometric characteristics are key indicators of plant nutrient acquisition strategies and environmental adaptation. Yet, their responses to long-term N deposition, especially the hierarchical variations across root orders, remain unclear, hindering a mechanistic understanding of root system plasticity. To assess root-order-specific responses of fine root C, N, and P concentrations and stoichiometric ratios to long-term N fertilization, a field experiment was initiated in 2014 in coastal Metasequoia glyptostroboides plantations in Jiangsu Province, eastern China, involving five N fertilization levels (0, 56, 168, 280, and 336 kg ha-1 yr-1). The results showed that N fertilization generally increased fine root N concentration, C/P and N/P ratios, and decreased P concentration and C/N ratio across root orders. Except for fine root C concentration, the absolute response ratios of fine root stoichiometric traits to N fertilization exhibited an increasing trend across root orders. The direct effects of N fertilization on the fine root stoichiometric characteristics were obviously higher than the indirect effects whether at the scale of entire root system, functional module or individual root order. Significant associations between fine root functional traits and stoichiometric characteristics were observed at the scale of entire root system, whereas such relationships were not evident at the scale of individual root order or functional module. Overall, the fine root stoichiometric characteristics responded more strongly with increasing root order under N fertilization, and interpretations of the drivers of these characteristics should be scale-explicit.

Tree species differ in their ability to use light efficiently, affecting carbon gain, establishment and survival in highly heterogeneous environments. This efficiency relies on the maintenance of the photosynthetic induction state, regulated by structural, biochemical, photochemical and stomatal processes that vary along the leaf economics spectrum (LES). Slow return species, such as shade-tolerant species (often late successional), are thought to sustain higher photosynthetic induction state, while quick return species, like light-demanding species (often early successionals) would have lower shade acclimation and shade-tolerant species lower acclimation to high light. Yet, results often deviate from these predictions. Moreover, most LES traits reflect steady state performance, not dynamic responses. Here, we investigated photosynthetic induction responses in four widely distributed Brazilian tree species representing contrasting successional groups and LES positions, grown under 10% light, 50% light and Full sun. We quantified induction dynamics in terms of CO2 assimilation, stomatal conductance, electron transport rate, as well as chlorophyll content, and leaf mass per area (LMA). Acclimation to distinct light environments was assessed using a shade adjustment coefficient and a novel metric based on Principal Component Analysis (PCA), Relative Plasticity (RP). RP suggests an asymmetrical bell-shaped relationship with LES position: the slow return Hymenaea courbaril showed low plasticity and little change in resource allocation (LMA), photosynthetic rates or induction times; the fast-return Schinus terebinthifolia, displayed moderate plasticity but unexpectedly high shade acclimation showing high induction state and CO2 assimilation rates; and the intermediate strategists Cecropia pachystachya and Handroanthus impetiginosus exhibited the highest plasticity, with coordinated increases in LMA, CO2 assimilation, conductance and photosynthetic induction under increasing light conditions. These findings highlight the importance of integrating photosynthetic dynamics into ecophysiological frameworks for species selection in reforestation, particularly in heterogeneous light environments, where adaptive flexibility can play a critical role on the resilience of an ecosystem.

Seasonal climate warming affects temperate plant phenology differently. Early winter warming can delay dormancy release and budburst due to insufficient chilling, while late winter or spring warming advances budburst. Additionally, the influence of pre-spring non-structural carbohydrate (NSC) availability on leaf phenology remains poorly understood. We explored the effects of previous late-summer defoliation and winter-spring warming on NSC dynamics and spring leaf phenology in two species: deciduous sessile oak with low chilling sensitivity and evergreen Scots pine with intermediate chilling sensitivity. We observed species-specific responses of leaf phenology to warming and defoliation. Winter warming delayed leaf unfolding in pine but not in oak, likely reflecting the greater chilling requirement of the pine. Defoliation significantly reduced pre-spring NSC levels in twigs and roots of both species, and led to earlier needle emergence in pine, with no impact on oak's leaf out date. Our findings indicate a dual dependency of pine leaf unfolding on temperature and internal carbon reserves, suggesting that defoliation, e.g., through herbivory or diseases, affects the following year's spring phenology and leaf growth in evergreen species but not in deciduous trees. These findings are important for understanding the adaptive strategies of different plant functional types under uneven warming conditions.

Tree species mixing has been widely recognized as an effective silvicultural strategy for enhancing both stand productivity and biodiversity. Nevertheless, its effects on branch radial growth and the underlying physiological mechanisms remain inadequately understood. In this study, we measured branch ring widths and 22 functional traits of pure and mixed plantations of Pinus massoniana and Castanopsis hystrix to investigate the effects of species mixing on branch radial growth, to assess potential variations between even- and uneven-aged forest mixtures, and to elucidate the underlying physiological mechanisms. Our results demonstrated that tree species mixing generally promoted branch radial growth, as indicated by the basal area increment for both studied species. The effect of species mixing on branch radial growth was not significantly different between even- and uneven-aged mixtures for C. hystrix; however, it diminished with increasing age of P. massoniana. Our findings indicated that the radial branch growth of P. massoniana was related to larger tracheid radial diameter and higher hydraulic conductance. In contrast, increased branch radial growth of C. hystrix was more related to higher specific leaf area and thinner leaves in mixed plantations, which potentially improved the light capture efficiency and leaf carbon turnover rate. Our results also indicated that tree species mixture is an effective strategy for enhancing branch growth. The positive mixing effect could diminish as P. massoniana reaches an over-mature age in the mixed-species stand, implying that species mixing practices during the early stages of stand development provide more benefit. The findings provide valuable insights for formulating reasonable forest management strategies and improving the understanding of the eco-physiology of species mixing effects on tree growth.

Drought stress severely impacts the growth, yield, and quality of apple (Malus domestica). Abscisic acid (ABA) and basic helix-loop-helix (bHLH) transcription factors play crucial roles in regulating the drought response in many plants, but the potential interactions between bHLH and ABA in response to drought in apple still need to be discovered. Herein, we identified a bHLH transcription factor, ORG2 (OBP3-responsive gene 2), from M. hupehensis, and the expression of which is induced by drought and ABA. Apple plants that overexpressed MhORG2 were more sensitive to drought stress, while silencing MhORG2 caused the opposite phenotype. Specifically, we found that MhORG2 could directly bind to the DRE element in the MhAAO3 promoter and repress its expression, thereby ultimately reducing drought tolerance. Furthermore, MhORG2 represses the expression of antioxidant enzyme genes (MhSOD, MhAPX1, and MhCAT), leading to the accumulation of reactive oxygen species (ROS) and consequently reducing the drought tolerance of apple plants. Our findings uncover a novel mechanism by which MhORG2 negatively regulates drought tolerance in apple plants, offering a potential target for the development of drought-tolerant crops via biotechnological approaches.

Mangroves are vital components of coastal blue carbon ecosystems due to their high carbon sequestration capacity, offering a nature-based strategy for climate change mitigation and adaptation. However, their photosynthetic carbon assimilation is highly susceptible to increased salinity. Previous studies have shown that the net photosynthesis rate (Anet) in mangrove plants under salt stress was limited by stomatal conductance (gs) and biochemical factors, but the role of mesophyll conductance to CO2 (gm), -a diffusion component increasingly highlighted as a significant constrain on photosynthesis in various plant species-has not been explicitly considered. In this study, we revisit the physiological mechanisms underlying photosynthetic response of mangrove plants to salt stress. We experimentally examined variations in a comprehensive set of photosynthetic parameters (i.e., with gm included) and leaf structural components in two common coastal woody species of southern China, Kandelia obovata and Aegiceras corniculatum, across different salinity gradients. Our results demonstrate that both species exhibited optimal photosynthetic performance at 10‰ salinity; however, A, gₛ, gₘ, and significantly declined with increasing salinity level. However, maximum carboxylation rate (Vcₘₐₓ) did not decrease significantly in K. obovata, while it showed a significant decline in A. corniculatum. Photosynthetic limitation analysis showed that gₘ was the dominant limiting factor across salinity treatments, except in Kandelia obovata at 20‰ salinity. In K. obovata, the decline in gₘ correlated with reductions in chloroplast surface area exposed to intercellular airspace per unit leaf area (Sc/S), whereas no such structural relationship was observed in A. corniculatum. Overall, our results demonstrate that increased mesophyll resistance to CO2 diffusion was a primary cause of photosynthetic decline under salt stress, with species-specific structural regulation of gₘ. These findings enhance our understanding of mangrove responses to salinity and providing guidance for species selection and management strategies to maintain productivity and carbon sequestration in coastal blue carbon ecosystems under future climate change.

Drought-induced tree mortality and dieback is expected to become an increasingly significant issue as climate change increases the frequency, severity and duration of droughts. The primary proposed mechanism of drought-induced decline is hydraulic failure, which is mechanistically linked to xylem architecture. However, annual variation of xylem anatomical traits has largely been overlooked as a possible driver of tree decline, with a focus instead on traditional ring-width based dendrochronological methods. Here, we employ a quantitative wood anatomy approach to examine whether differences in xylem vessel lumen area were related to decline risk during a recent drought-induced decline of chestnut oak from Southern Indiana, USA. Our results show that over at least the past 60 years, healthy trees built consistently wider vessels than those which succumbed. This phenomenon has now been observed across three continents, and in both tracheid and vessel bearing species, indicating that conduit size may be related to drought survival, likely as an indicator of long-term stress. Moreover, an analysis of the sensitivity of vessel lumen area to climate variables suggests that early winter warming may promote the production of wider vessels in the following year. In contrast, a negative correlation between prior year growing season length and vessel lumen area suggests that extended growing seasons may lead to narrower, potentially more vulnerable xylem vessels. These effects were less pronounced in the declining trees, hinting that already-stressed trees were less sensitive or physiologically unable to respond to climatic variability. Designing studies aimed at understanding the drivers of intra-specific variation in xylem conduit architecture could improve our ability to predict tree dieback and mortality under future climate scenarios.

Trichoderma is reported to enhance plant salt adaptability, but the mechanisms still need in-depth investigation. This study was to dissect how Trichoderma asperellum manipulated root ions exchange in salt-stressed wolfberry to satisfy nitrogen acquisition and preserve K+/Na+ homeostasis. Trichoderma agent (TA) was supplemented around the roots of potted plants, and salt stress was conducted by watering with NaCl solution. Salt adaptability of wolfberry was enhanced by T. asperellum, as TA supplement protected photosynthesis, alleviated biomass reduction and increased tissue N accumulation and K+/Na+ under salt stress. Consistently, T. asperellum enhanced root Na+ extrusion and K+ retention in salt-stressed wolfberry, which was related to Na+/H+ antiporter and K+ outward-rectifying channels, as pretreatments with their inhibitors depressed root Na+ efflux but caused K+ efflux. Considering inhibited plasma membrane (PM) H+-ATPase synchronously dampened root Na+ extrusion and K+ retention under salt stress, T. asperellum was inferred to enhance root Na+ extrusion and K+ retention in salt-stressed wolfberry by inducing PM H+-ATPase. Elevated root plasma membrane H+-ATPase activity by T. asperellum was actually observed in salt-stressed wolfberry and had nothing with constitutive transcript expression. The activated H+-ATPase by T. asperellum also provided more driving force for H+/NO3- symporter and increased root NO3- absorption. T. asperellum prevented salt-induced great root NH4+ efflux and retained mild NH4+ influx likely because NH4+ efflux was not required for restricting Na+ entry. Overall, T. asperellum activated root plasma membrane H+-ATPase to optimizing root ions exchange and then improved nitrogen acquisition and K+/Na+ homeostasis in wolfberry under salt stress. According to the structural equation model analysis, PM H+-ATPase had positive effect on photosynthesis, root sugar content, root respiration and itself sequentially, highlighting that the activated root PM H+-ATPase by TA supplement enhanced wolfberry salt adaptability by droving a favorable cooperation between roots and aerial part.

Indian sandalwood (Santalum album) is an economically important facultative parasite that develops a specialized multicellular organ, the haustorium, to absorb water and nutrients from its hosts. To elucidate the molecular mechanisms underlying haustorium development, we conducted a transcriptome analysis across six S. album tissues. We found that SaRac1, encoding a functional small GTPase, is specifically expressed in the haustorium. We employed host-induced gene silencing (HIGS) by generating transgenic poplar (Populus alba × P. glandulosa) hosts that express hairpin RNAs to target and downregulate SaRac1 in the parasite. S. album grown with SaRac1 RNAi transgenic host plants exhibited significantly suppressed haustorium development compared to those grown with wild-type or empty-vector controls. Mechanistically, SaRac1 interacts with SaRbohA, and this interaction synergistically enhances ROS production. Exogenous H₂O₂ application significantly upregulated key haustorium formation-related genes. In contrast, the Rboh inhibitor diphenyliodonium chloride (DPI) suppressed the expression of SaYUCCA and SaSBT in S. album grown with wild-type and empty-vector control hosts, thereby reducing haustorium formation. In S. album plants grown with RNAi hosts, SaSBT and SaEXPA were also downregulated by DPI application. Our findings identify a crucial mechanism whereby SaRac1 promotes haustorium formation by modulating ROS signaling and provide novel insights into the molecular physiology of plant parasitism.

Leaf nutrient resorption represents a vital nutrient conservation strategy for plants. While trace element resorption patterns have been extensively studied in upland terrestrial plants, they remain poorly characterized in mangrove ecosystems. This study investigated the nutrient resorption efficiency (NuRE) of seven trace elements-iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), boron (B), sodium (Na) and aluminum (Al)-in mangroves, comparing them with upland terrestrial plants and evaluating their ecological implications under seasonally dry and wet conditions. Field sampling was conducted in Dongzhaigang National Nature Reserve, China, across dry and wet seasons, and green and senesced leaves from 10 mangrove species were analyzed. Our findings revealed distinct resorption strategies between mangroves and upland terrestrial plants. Compared with upland terrestrial species, mangroves presented net accumulation (negative NuRE) of Na (-29.06 ± 6.87%), Mn (-72.71 ± 11.79%), B (-77.36 ± 14.49%), Fe (-123.63 ± 17.98%) and Al (-164.91 ± 33.21%), demonstrating significantly lower NuRE values for these elements. In contrast, mangroves presented a greater NuRE for Cu (57.80 ± 3.50%) than their upland terrestrial counterparts did, whereas Zn resorption (17.39 ± 4.00%) did not differ significantly between the two systems. Our analysis revealed that Na resorption patterns exhibited strong seasonal variations across ecological gradients. During dry seasons, Na accumulation (more negative NaRE) was significantly greater in low intertidal zones, tree species and isobilateral leaves (characterized by symmetrical mesophyll organization). In contrast, wet seasons completely reversed these patterns, favoring accumulation in high intertidal zones, shrubs and bifacial leaves (with dorsiventral mesophyll organization). Green-leaf nutrient concentrations emerged as the primary driver of NuRE, outweighing soil nutrient availability across dry and wet seasons. These findings highlight mangroves' unique nutrient conservation strategies and underscore the importance of foliar nutrient status in predicting ecosystem resilience under seasonal hydroclimatic variations.

Climate change-induced shifts in plant phenology have substantially impacted terrestrial ecosystem structure and function. While the effects of drought and heatwaves on leaf senescence have been studied, the response of leaf senescence to compound drought and heatwave events remains poorly understood, especially due to a lack of experimental evidence. In this study, we investigated the responses of leaf senescence to varying durations (13, 28, and 43 days) of compound drought and heatwave stress in saplings of three temperate deciduous tree species. We found that prolonged drought and heatwave conditions delayed leaf senescence by 20.2 in Koelreuteria paniculata and 22.4 days Hibiscus syriacus, respectively, potentially as a compensation for stress-induced reductions in growth. However, leaf senescence in the lowly tolerant Acer palmatum shifted from delayed to advanced, indicating a nonlinear response. Total photosynthesis, relative height increment, and basal diameter growth decreased in all three species, with the strongest reductions in Acer palmatum, followed by Hibiscus syriacus and Koelreuteria paniculata. Our findings demonstrate delayed effects of environmental stress on leaf senescence and highlight species-specific variation in response to compound drought-heatwave events, providing insights into how plants respond to climate change.

Tea plant is an important thermophilic crop in China. Understanding the cold response mechanisms will be helpful to improve the yield and tea quality against cold stress. Orphan genes, which lack homologs in other lineages, play critical contributions in plant environmental adaptability, yet the characteristics and roles of orphan genes in tea plants, particularly regarding cold tolerance, remain largely unexplored. In the current study, we systematically identified 2,793 orphan genes of tea plant using both genomic and transcriptomic datasets. These orphan genes exhibited simpler gene structures, shorter lengths, fewer introns, higher isoelectric points and lower expression abundance compared to the evolutionary conserved genes. We further characterized an orphan gene named CsOG3 that may play roles in tea plant cold resistance. Silencing of CsOG3 reduced the cold tolerance level of tea plant seedlings, while overexpression of CsOG3 significantly enhanced the cold resistance of tobacco and tea plants. By regulatory elements and expression correlation analysis, we identified a cold induced MYB transcription factor-CsMYB44, which is involved in regulating CsOG3. Functional validation using dual-luciferase reporter and Yeast one-hybrid assays reveal that CsMYB44 could bind to the promoter and directly activate the expression of CsOG3. In vivo repression of CsMYB44 also significantly reduced the cold tolerance of tea plants. This report comprehensively presented the architecture of tea plant orphan genes and highlighted the contribution of CsOG3 modulated by CsMYB44 against the cold stress in tea plants, broadening our understanding of plant orphan genes and the contribution in environmental adaptation.

Sexual dimorphism in dioecious species can shape divergent hydraulic strategies in response to environmental stress, yet integrative studies linking anatomical and physiological traits across different plant organs remain scarce. We investigated sex-specific water-use strategies in two Mediterranean shrubs, Pistacia lentiscus L. and Rhamnus alaternus L., by analyzing leaf and wood anatomy, leaf functional traits, gas exchange, and chlorophyll fluorescence. Male plants of both species exhibited conservative morpho-anatomical traits, including smaller, thicker leaves, lower specific leaf area (SLA), higher dry matter content, and reduced intercellular spaces, traits typically associated with drought resistance strategies. In P. lentiscus, these traits correlated with higher photosynthetic rates and Fv/Fm values, alongside greater stomatal density and vessel frequency, suggesting coordinated investment in carbon gain and hydraulic efficiency/safety. Conversely, females displayed acquisitive traits (higher SLA, wider intercellular spaces, lower vessel frequency), potentially enhancing photosynthesis under mesic conditions but increasing vulnerability to drought-induced embolism. In R. alaternus, female individuals maintained higher net photosynthesis and iWUE, while males exhibited greater Fv/Fm and a decoupled leaf-wood coordination. These findings suggest that males may adopt safer hydraulic architectures, while females, potentially constrained by reproductive demands, pursue efficiency-driven strategies, still maintaining vessel redundancy in wood. As aridity intensifies in Mediterranean regions, such dimorphism may influence population dynamics, sex ratios, and species resilience. Our results underscore the ecological significance of species-specific sex-based hydraulic variation and the necessity of incorporating sex into trait-based models of plant responses to climate change.

Ectomycorrhizal (ECM) fungi, as major carbon (C) sinks, are critical to plant-soil C cycling. Although C allocation between plants and ECM fungi has been studied extensively, C transport time, the key component of C cycling, remains limited understanding. To address this, we collected new needles (weekly), roots (monthly) and ECM fungi (sporocarps and hyphae) of three genera (Cortinarius, Lactarius, and Russula) in a boreal Scots pines (Pinus sylvestris L.) forest in Finland. We analyzed the natural abundance C isotope composition (δ13C) of sugars or organic matter and observed a strong vapor pressure deficit (VPD) signal in needle sucrose δ13C. We coupled VPD with the δ13C of water-soluble carbohydrates (WSC, δ13CWSC) in sporocarps to determine C transport times. We found Lactarius and Russula, with short hydrophilic mycelia that enable efficient solutes uptake, had transport times of 6-13 days, peaking at 8 days. In contrast, Cortinarius, with extensive hydrophobic mycelia that limit water and solute movement, showed slower transport times of around 18 days. The different transport time is likely attributable to a more extensive mycelial network and potentially higher C demand in Cortinarius compared to Lactarius and Russula. The three genera also showed a marginally significant effect on δ13CWSC in sporocarps (P = 0.06, ANCOVA). This study highlights that natural abundance δ13C analysis offers a practical alternative to pulse-labeling for estimating C transport time in complex plant-fungal interactions where the latter is difficult to implement. The longer transport time of Cortinarius compared to Lactarius and Russula is critical during periods of reduced photosynthesis, when limited C supply makes fast allocation essential for sustaining belowground metabolism. Slower transport may weaken its role and reduce forest productivity in boreal forests with short growing seasons. As global warming favors Cortinarius, its longer C transport time may impede soil C cycling and nutrient turnover.

Understanding the factors and processes of tree water use at night is critical for sustainable fruit production and ecological protection within the context of increasing global climate extremes. A long-term experiment was set up in China's Loess Plateau region on rainfed fruit trees - jujube (grown under arid, semi-arid conditions) and apple (grown under semi-humid, drought-prone conditions). Data were collected under both wet and dry conditions and then analyzed for total sap flow (Q), daytime sap flow (Qd), nighttime sap flow (Qn), and the related components of nighttime canopy transpiration (QTn) and nighttime water recharge (QRn). The results showed that the percentage fraction of Qn to Q was 27.6% for jujube and 20.9% for apple. For jujube, QTn/Qn was 67.5%, which was higher than that of apple (56.9%), a species that was relatively under humid conditions. At annual scale, higher annual precipitation (P) resulted in higher Qd but lower Qn. At the daily scale, the components of Qn were positively correlated with leaf area index (LAI) but negatively correlated with solar radiation (Rs) and vapor pressure deficit (VPDn) for jujube at Mizhi Station. Under low LAI/Rs conditions, Qn components of jujube trees had negative correlation with soil water content (SWC). The components of Qn are positively correlated with SWC for apple at Luochuan Station. Under adequate SWC, QRn increased with increasing Qd for apples. Structural Equation Modeling (SEM) suggested that the main drivers of nighttime water use were similar for the two fruit trees, but with stronger direct effect of LAI on Qn for jujube. Moreover, Rs mainly affected Qn/Q and QTn/Q through an indirect pathway in jujube, while both its direct and indirect effects were strong and almost equivalent in apple. The findings are critical for the management of fruit trees in ecological environments under worsening environmental conditions.

Soil fungi establish symbiotic associations with plant roots, which provide nutrients in exchange for photosynthate from the host. Despite the recognized importance of fungal symbiosis, how root-associated fungal communities respond to light qualities remains unclear. In this study, we conducted on a novel spectral attenuation experiment involving seedlings of two temperate tree species, Quercus mongolica (ectomycorrhizal, ECM) and Acer mono (arbuscular mycorrhizal, AM). The experimental design incorporated five spectral treatments, including ambient full-spectrum as control and various attenuations of ultraviolet (UV) and visible light. We quantified tree growth and root traits, and profiled root-associated fungal communities through high-throughput sequencing. Results showed that tree growth and root traits varied depending on tree species and spectral treatments. Blue light significantly promoted total biomass of Q. mongolica, but reduced root exudative carbon, sugar and phenolics. In contrast, A. mono showed no spectral changes in biomass and had the lowest root exudative sugar and phenolics in control. Higher root exudative carbon and phenolics were observed in A. mono than in Q. mongolica. Root-associated fungal communities also showed distinct responses to spectral treatments and tree species. Sob's and Chao1 indices of Q. mongolica fungal communities were significantly lower than those of A. mono under UV attenuation, and alterations in community structure were more pronounced in A. mono. These changes were strongly associated with root traits, particularly exudative carbon, sugar, and total phenolics. Within fungal communities, Q. mongolica was dominated by ECM and saprotrophic fungi, and A. mono by AM and saprotrophic fungi. The relative abundance of ECM fungi in Q. mongolica and that of AM fungi in A. mono was lowest when UV-B radiation was attenuated. In total, these findings highlight the crucial role of root traits and their interaction with fungi when exploring plant adaptation to varying light environments.