Search Results (31)

Grazing is a pervasive disturbance in arid ecosystems, but its effects on community-level coordination of plant hydraulic and economic traits remain poorly understood. Here, we investigated how long-term grazing alters community-weighted mean hydraulic and leaf economic traits in a desert steppe of Inner Mongolia, and how these shifts affect aboveground biomass (AGB) and water-use efficiency (WUE). Grazing drove a coordinated conservative shift in community hydraulic traits, including more negative osmotic potential at turgor loss point (ψ_tlp), increased cell wall rigidity (ε), and reduced leaf hydraulic conductance (K_leaf). Grazing also restructured trait–function relationships: under grazing, AGB was positively correlated with dehydration tolerance rather than transport efficiency, and WUE was tightly coupled with osmotic adjustment. Variance partitioning showed that hydraulic traits explained 57.4% of AGB variation under grazing, whereas economic traits dominated in the control site (74.5%). Our findings demonstrate that long-term grazing imposes a fundamental reorganization of community-level trait coordination, driving a transition from an efficiency-oriented to a safety-oriented strategy, and highlight the central role of hydraulic traits in mediating ecosystem function under combined stress. Full article

Frequent co-occurrences of high temperature and drought in tropical regions make heat and drought tolerance of landscape plants core physiological traits that determine their landscape adaptability and community stability. However, systematic elucidation of the differentiation patterns of stress resistance between specialist and generalist tropical landscape plant species, the intrinsic correlations between heat and drought tolerance traits, and the regulatory mechanisms of leaf functional traits remains lacking. In this study, eight typical tropical landscape plant species in Xishuangbanna Tropical Botanical Garden were selected as research objects. By determining leaf chlorophyll fluorescence parameters, water relation parameters and leaf functional traits, we systematically analyzed the differences in heat and drought tolerance and interspecific differentiation characteristics between specialist and generalist species, and simultaneously elucidated the correlation patterns of drought-heat tolerance traits as well as the regulatory effects of leaf functional traits on these traits. The results showed that the turgor loss point water potential (Ψ_TLP) of generalist tropical landscape plant species was significantly higher than that of specialist species, with superior drought tolerance; in contrast, the half-lethal temperature of photosystem II (T50) of specialist species was significantly higher than that of generalist species, with stronger heat tolerance. Among the eight tested species, Bombax ceiba exhibited the strongest drought tolerance, while Baccaurea ramiflora had the optimal heat tolerance. The study also found that the drought and heat tolerance traits of tropical landscape plants exhibited stress-specific trade-offs; leaf functional traits had limited overall explanatory power for the stress resistance of tropical landscape plants and only exerted a certain regulatory effect on drought tolerance. This study clearly reveals the differences in heat and drought tolerance between specialist and generalist species. This finding not only enhances our mechanistic understanding of stress resistance in tropical plants but also provides data support for ecological restoration and conservation practices in tropical gardens. Full article

Barley lodging—specifically stem lodging—occurs when the bending moments from wind and ear weight exceed the culm’s load-bearing capacity. Lodging risk decreases as plant height decreases and culm strength increases. Geometry (stem diameter, culm wall thickness) and material strength determine culm bending strength. By studying changes in stem mechanical properties (at three positions along the culm) in two genotypes (grown in a greenhouse), we found that culm strength (assessed with a three-point bending test) slightly diminished through ripening owing to a decline in both area moment of inertia (i.e., strength due to geometry alone) and apparent material strength, presumably due to turgor loss. When the stem segments collected from fully ripe plants were dried to a moisture content typical of harvest maturity, however, strength rose to a maximum. Thus, minimum stem bending resistance occurs during a window in which plants are fully ripe but have not yet reached harvest-dry moisture content. Hence, in the absence of rain—which would severely reduce the mechanical strength of dry, ripe plants—the physiological risk of stem lodging is highest when the crop is fully ripe but not yet harvest-dry. However, the actual lodging risk increases as harvest approaches, because summer storms are frequent at this time of year and dry straw loses rigidity when wetted. Full article

Liquidambar formosana Hance, a tree species in subtropical broad-leaved forests, exhibits a striking autumn leaf coloration. However, how drought stress during this period influences leaf color change remains poorly understood. In this study, two-year-old seedlings were subjected to four drought gradients. Leaf color parameters, pigment contents, cellular structure, photosynthetic physiology, and hydraulic properties were systematically measured throughout the leaf color transition period. The results show that, with increasing drought severity, leaf red-green coordinate a* increased significantly during early-to-middle stress (S1–S3), while lightness L* and yellow-blue coordinate b* increased at late stress (S4). Chlorophyll (Chl) content continuously decreased, anthocyanins (Ant) peaked at mid-stress, and carotenoids (Car) became enriched at late stress. Leaf cellular structure and hydraulic parameters declined, photosynthetic function was inhibited, and antioxidant enzyme activities showed an initial increase followed by a decrease. Correlation analysis and Random Forest models revealed that L* was strongly associated with superoxide dismutase (SOD) activity, carotenoid-to-chlorophyll (Car/Chl) ratio, and net photosynthetic rate (P_n); a* was closely linked to osmotic potential at full saturation (Ψ_sat), relative water content at the turgor loss point (RWCtlp), SOD activity, Car/Chl ratio, anthocyanin-to-chlorophyll (Ant/Chl) ratio, Ant content, transpiration rate (T_r), P_n, and main vein thickness (Mvt), while b* was primarily correlated with Ψ_sat, Car/Chl ratio, SOD activity, Ant/Chl ratio, and P_n. These statistical associations suggest multiple physiological processes are involved in leaf color change. Based on these findings, we propose a hypothetical sequence: drought initially disrupts leaf water status, leading to structural atrophy and hydraulic decline, followed by photosynthetic inhibition, activated antioxidant defense, and altered pigment accumulation, which are correlated with the sequential leaf color transition from green to red to yellow-orange in this species. Full article

Intergeneric hybridization of Vanda and Papilionanthe holds promise for pyramiding superior ornamental and stress-tolerant traits, though systematic studies on their hybrids remain scarce. Using Vanda lamellata var. Boxallii (♀), Papilionanda ‘Hetty Henderson’ (♂), and 72 progenies, we investigated parent–progeny relationships via iPBS markers, spectral phenomics, and morphology, alongside floral water balance and thermotolerance. Six iPBS primers amplified 90 bands (92.98% polymorphism), confirming high genetic diversity. Spectral reflectance (400–1000 nm) revealed organ-specific genetic differentiation. Clustering analyses consistently indicated that progenies were genetically and phenotypically closer to the female parent, with spectral/morphological patterns matching genetic groupings. Resistance evaluations showed progenies had significantly stronger floral water storage capacity than both parents, while the female parent excelled in water transport traits. Progenies developed thicker petal/sepal cuticles, though the male parent exhibited superior thermotolerance indices. This study clarifies the genetic regulation of stress resistance in these hybrids, providing critical support for precise early screening in orchid breeding. Full article

Plant leaf drought tolerance is regulated by the coordinated effects of water transport efficiency, transpirational water loss, and hydraulic safety. Although cotton is considered drought-tolerant, the mechanisms that coordinate water transport and gas exchange to confer drought tolerance remain incompletely understood. In this study, four soil moisture gradients were established under field conditions and maintained consistently throughout the growing season. The relationships among leaf turgor loss point (Ψ_tlp), gas exchange, and hydraulic traits were examined in two cotton cultivars at the peak flowering stage. With increasing drought treatments, Ψ_tlp, stomatal aperture ratio (g_ratio), leaf hydraulic conductance (K_leaf), leaf hydraulic conductance inside the xylem (K_x) and leaf hydraulic conductance outside the xylem (K_ox) declined significantly, with K_x showing the greatest reduction. Both K_x and g_ratio were strongly positively correlated with Ψ_tlp. Anatomically, vein density (D_v) and vessel number (Np) increased, whereas xylem vessel area (Ap) decreased. The reduction in Ap was the primary structural factor driving the decline in K_x and contributing to lower Ψ_tlp. We conclude that cotton enhances drought tolerance through a coordinated hydraulic and osmotic strategy, by modifying xylem anatomy (reducing Ap) to downregulate K_x and by adjusting osmotically to depress Ψ_tlp. The synergistic reduction in K_x and g_ratio slows the decline in leaf water potential, thereby delaying Ψ_tlp and enhancing leaf hydraulic safety during drought. This integration optimizes stomatal regulation and water transport while ensuring hydraulic safety. The findings provide a key theoretical basis and potential breeding targets for the targeted improvement of drought tolerance and water use efficiency in cotton. Full article

Despite the progress to understand drought tolerance worldwide, the response of urban trees to the increased frequency and severity of droughts, particularly in tropical regions, remains unclear. Such an evaluation is essential for predicting future urban forest dynamics. The leaf turgor loss point (π_TLP), leaf safety margins (SMs) and their relationship with functional traits were measured in ten native tree species during wet and dry seasons in a tropical urban environment. We detected interspecific variation in tree responses related to desiccation tolerance and desiccation avoidance as strategies to resist drought. Desiccation avoidance was linked to lower adjustment of midday water potentials and water-conservative traits such as high wood density, low specific leaf area (SLA), and high leaf dry matter content, while species with more negative π_TLP maintained stomatal conductance and growth despite decreasing leaf water potentials. Although the differences between predawn and midday potentials during the dry season suggest that severe drought does not occur, some species showed negative safety margins. This indicates that while some urban trees can tolerate or avoid current dry periods, continued climate change may push certain species beyond their safe operating range, making species selection for urban planning increasingly critical. Full article

Estimating leaf water potential (Ψ_leaf) is essential for understanding plant physiological processes’ response to drought. The estimation of Ψ_leaf based on different regression analysis methods with hyperspectral vegetation indices (VIs) has been proven to be a simple and efficient technique. However, models constructed by existing methods and VIs still face challenges regarding the generalizability and limited ranges of field experiment datasets. In this study, leaf dehydration experiments of three maize cultivars were applied to provide a dataset covering a wide range of Ψ_leaf variations, which is often challenging to obtain in field trials. The analysis screened published VIs highly correlated with Ψ_leaf and constructed a model for Ψ_leaf estimation based on three algorithms—partial least squares regression (PLSR), random forest (RF), and multiple linear stepwise regression (MLR)—for each cultivar and all three cultivars. Models were constructed using PLSR and MLR for each cultivar and PLSR, MLR, and RF for the samples from all three cultivars. The performance of the models developed for each cultivar was compared with the performance of the cross-cultivar model. Simultaneously, the normalized ratio (ND) and double-difference (DDn) were applied to determine the VIs and models. Finally, the relationship between the optimal VIs and Ψ_leaf was analyzed using discontinuous linear segmental fitting. The results showed that leaf spectral reflectance variations in the 350~700 nm bands and 1450~2500 nm bands were significantly sensitive to Ψ_leaf. The RF method achieved the highest prediction accuracy when all three cultivars’ data were used, with a normalized root mean square error (NRMSE) of 9.02%. In contrast, there was little difference in the predictive effectiveness of the models constructed for each cultivar and all three cultivars. Moreover, the simple linear regression model built based on the DDn(2030,45) outperformed the RF method regarding prediction accuracy, with an NRMSE of 7.94%. Ψ_leaf at the breakpoint obtained by discontinuous linear segment fitting was about −1.20 MPa, consistent with the published range of the turgor loss point (Ψ_TLP). This study provides an effective methodology for Ψ_leaf monitoring with significant practical value, particularly in irrigation decision-making and drought prediction. Full article

Poplars and aspens (Populus L. spp.) are undervalued options for use in managed landscapes. The genus comprises a multitude of taxa often negatively associated with disease susceptibility and short lifespans; however, it also hosts a diverse range of abiotic stress tolerances. The objective of this study was to generate a relative scale of the predicted drought tolerance of Populus spp. to inform site and taxon selection in managed settings. Utilizing vapor pressure osmometry, this study examined seasonal osmotic adjustment and predicted leaf water potential at the turgor loss point (Ψ_po) among several Populus taxa. All evaluated taxa demonstrated the ability to osmotically adjust (ΔΨ_π100) throughout the growing season. Bigtooth aspen (P. grandidentata Michx.) exhibited the most osmotic adjustment (−1.1 MPa), whereas black cottonwood (P. trichocarpa Torr. & A. Gray ex Hook.) exhibited the least (−0.44 MPa). Across the taxa, the estimated mean Ψ_po values in spring and summer were −1.8 MPa and −2.8 MPa, respectively. Chinese aspen (P. cathayana Rehder) exhibited the lowest Ψ_po (−3.32 MPa), whereas black cottonwood exhibited the highest (−2.47 MPa). The results indicate that drought tolerance varies widely among these ten Populus species and hybrids; bigtooth aspen and Chinese aspen are the best suited to tolerating drought in managed landscapes. Full article

Arid and semiarid ecosystems face significant water scarcity due to high evaporation rates exceeding precipitation. This study examines temporal variations in water relations of two woody species, Vachellia schaffneri (S. Watson) Seigler & Ebinger, and Prosopis laevigata (Humb. & Bonpl. ex Willd.) M.C. Johnst, and one epiphyte, Tillandsia recurvata (L.) L. (Bromeliaceae), to assess their drought tolerance and water storage capacity. We hypothesized that species with greater water storage capacity would exhibit lower drought tolerance due to reduced osmotic adjustments, whereas species with lower storage capacity would maintain turgor through osmotic regulation and cell wall rigidity. Predawn and midday water potentials (Ψ_pd, Ψ_md) were measured, and pressure–volume (P–V) curves were used to derive parameters such as saturated water content (SWC), osmotic potential (π_o), turgor loss point (Ψ_TLP), relative water content at Ψ_TLP (RWC_TLP), bulk modulus of elasticity (ε), and full turgor capacitance (C_FT). Significant correlations were found between C_FT and Ψ_TLP (positive), π_o (positive), and ε (negative). P. laevigata and T. recurvata exhibited higher water storage capacities (41.46 and 26.45 MPa⁻¹, respectively) but had a lower ability to maintain cell turgor under drought conditions. In contrast, V. schaffneri exhibited the lowest water storage capacity (11.88 MPa⁻¹) but demonstrated the highest ability to maintain cell turgor (Ψ_TLP = −1.31 MPa) and superior osmotic adjustments (π_o = −0.59 MPa). Both V. schaffneri and P. laevigata exhibited rigid cell walls, whereas T. recurvata displayed greater elasticity in its cell structures. The lowest moisture content in V. schaffneri suggests increased flammability and fire spread potential. Future studies should focus on live fuel moisture content across more species, explore seasonal variations in hydraulic traits, and integrate these physiological parameters into fire risk models to enhance wildfire prediction and management. Full article

Coffea canephora genotypes adopt distinct strategies to cope with drought and rehydration. We hypothesized that the greater drought tolerance of genotype ‘3V’ compared to ‘A1’, previously reflected in physiological and anatomical leaf traits after two water-stress (WS) cycles, could also be observed in P–V curve responses, root and branch anatomy, leaf midrib elongation (CVL), and root distribution. The ‘3V’ and ‘A1’ plants were grown under well-watered (WW) conditions and two cycles of water stress (WS). The ‘3V’ was more sensitive to WS, with reduced branch xylem vessel density (BXVD), while ‘A1’ demonstrated increased BXVD. Root xylem vessel area (RXVA) decreased to a greater extent in ‘3V’ than in ‘A1’, and both genotypes showed increased bulk elastic modulus. Regardless of water conditions, ‘A1’ maintained a higher relative leaf water content at the turgor loss point (RWC_TLP). Morphological acclimation did not occur in the second WS cycle. The ‘3V’ plants developed greater root mass in deeper soil layers than ‘A1’ under the WS condition. These findings suggest that ‘A1’ follows a conservative drought-avoidance strategy with lower physio-morphological plasticity, while ‘3V’ exhibits greater drought tolerance. Such responses highlighted coordinated physiological, morphological, and anatomical adaptations of the above- and below-ground organs for resource acquisition and conservation under WS. Full article

Pteroceltis tatarinowii Maxim is a famous paper-making tree endemic to China with a wide distribution. Leaves of this tree growing in different habitats show a certain plasticity, which is important for their ecological adaption. Here, the photosynthesis ability, hydraulic properties, and anatomy of P. tatarinowii leaves from a limestone forest (Langya Mountain) and a cultivated forest (Xiaoling Village) in Anhui province were compared. The results showed that leaves from Xiaoling Village had higher net photosynthesis rate and hydraulic conductivity, which were closely related to their higher vein density, stomatal density and palisade tissue thickness than leaves from Langya Mountain. However, lower leaf water potentials at turgor loss point and at 50% loss of conductivity, as well as a higher leaf hardness, for Langya Mountain leaves indicated their higher hydraulic safety and drought resistance than those of leaves from Xiaoling Village. This study reveals a hydraulic trade-off between efficiency and safety for P. tatarinowii leaves growing in distinct habitats. Further studies should include more habitats and different vegetation communities to clarify the ecological adaption so as to provide a scientific basis for the protection of this species. Full article

Poplar plantations can acclimate to drought stress in semi-arid areas, where the variation of stand age may result in varied water adaptation strategies presented as hydrodynamic performance. In this study, nine mature Populus simonii Carr. individuals were targeted as sampling objects in plantations characterized to three stand ages: young (9 yr), middle-aged (17 yr), and near-mature (29 yr) stages in a semi-arid area of western Liaoning, Northeast China. Hydraulic traits were investigated as parameters of leaf pressure-volume curves, xylem embolism vulnerability curves, hydraulic structure, and wood density (WD). Results showed that osmotic potential (Ψ_tlp) and relative water content at the turgor loss point and cell-wall bulk elastic modulus were lowest in middle-aged stands (−2.19 MPa; 86.71%; 13.75 MPa). Stem and leaf-specific hydraulic conductivity (K_s and LSC) were all the highest in middle-aged stands. Xylem embolism vulnerability (P₅₀) and lethal water potential of trees (P₈₈) increased with the growth of stand age. Young stands faced minimal risk of hydraulic failure according to the stomatal safety margin (SSM_tlp, Ψ_tlp minus P₅₀), which was consistent with the comprehensive evaluation results of the principal component analysis. WD was related to P₈₈ (R²= 0.51; p < 0.05). P₅₀ was related to drought avoidance traits Ψ_tlp (r = 0.76; p < 0.05) but not to xylem efficiency (K_s). Overall, WD can be an excellent proxy for hydraulic safety monitoring. Young and middle-aged Populus simonii populations are more adaptable to drought conditions than near-mature populations, and near-mature stands should receive intermediate cuttings to avoid exposure to drought stress. Full article

Little is known about how differences in water availability within the “super humid” tropics can influence the physiology of understory plant species and the composition of understory plant communities. We investigated the variation in the physiological drought tolerances of hundreds of understory plants in dozens of plant communities across an extreme elevation and precipitation gradient. Specifically, we established 58 understory plots along a gradient of 400–3600 m asl elevation and 1000–6000 mm yr⁻¹ rainfall in and around Manu National Park in southeastern Peru. Within the plots, we sampled all understory woody plants and measured three metrics of physiological leaf drought tolerance—turgor loss point (TLP), cuticular conductance (G_min), and solute leakage (SL)—and assessed how the community-level means of these three traits related to the mean annual precipitation (MAP) and elevation (along the study gradient, the temperature decreases linearly, and the vapor pressure deficit increases monotonically with elevation). We did not find any correlations between the three metrics of leaf drought tolerance, suggesting that they represent independent strategies for coping with a low water availability. Despite being widely used metrics of leaf drought tolerance, neither the TLP nor G_min showed any significant relationships with elevation or the MAP. In contrast, SL, which has only recently been developed for use in ecological field studies, increased significantly at higher precipitations and at lower elevations (i.e., plants in colder and drier habitats have a lower average SL, indicating greater drought tolerances). Our results illustrate that differences in water availability may affect the physiology of tropical montane plants and thus play a strong role in structuring plant communities even in the super humid tropics. Our results also highlight the potential for SL assays to be efficient and effective tools for measuring drought tolerances in the field. Full article

Earth’s forests are increasingly exposed to climate risks through climate change-related drought and heat waves. Here, we review the climate vulnerability of European beech (Fagus sylvatica), the most abundant tree species of Central Europe’s temperate forests, and its adaptation potential to a hotter and drier climate in northern Germany, close to the center of the species’ distribution range. About two-thirds of the studied beech forests show persistent negative growth trends of their dominant trees since the onset of rapid warming in the early 1980s, driven primarily by long-term deterioration of the climatic water balance (CWB) in summer and, locally, long-term decrease in June precipitation. Lower water storage capacity of the soil increases the climate sensitivity of growth. Even though beech populations of drier sub-regions reveal some acclimation to drought (reduced stomatal conductance, turgor loss point reduction, higher C allocation to roots), they are more climate-vulnerable than populations at moister sites, visible in larger growth decreases and greater CWB sensitivity of growth. Even though beech mortality is still lower in the study region than in other parts of Central Europe, our results identify beech forest regions with <350 mm growing-season precipitation as vulnerable to recent climate conditions, which refers to half of the study region. With further climate warming and aridification, most of northern Germany likely will become unfavorable for beech growth within the next tree generation, which suggests choosing in many production forests alternative, more drought- and heat-resistant timber species. Full article