Minimum Conductivity Research Articles

Temperature governs the relative contributions of cuticle and stomata to leaf minimum conductance.

During periods of stomatal closure, such as drought, plant leaves continue to lose water at a rate determined by the minimum leaf conductance, gmin. Although gmin varies with temperature, less is known about what drives this variation, including how the pathways of water loss (cuticle or stomata) vary with temperature. We used gas exchange and bench drying methods to measure gmin and cuticular conductance, gcw, across a wide temperature range (20-50°C) in 11 broadleaf species. Vapour pressure deficit (VPD) covaried with temperature from 0.83 to 10.7 kPa. The dominant pathway of water loss for gmin shifted from stomatal transpiration towards cuticular transpiration as temperature increased. Leaf traits had variable, temperature-dependent relationships with gmin and gcw, with trait-conductance relationships being generally stronger at higher temperatures. Cuticular thickness varied inversely with high-temperature gcw. Simulation results showed that gcw may impact photosynthetic capacity estimates, particularly in species with low stomatal conductance. The pathways of water loss in leaves during times of stomatal closure depend strongly on temperature. This effect may have large implications for landscape-scale water balance modelling and improving gas exchange measurements. We propose variation in VPD as a potential contributing factor in gmin and gcw variation among studies.

Contrasting strategies in morphological and physiological response to drought stress among temperate forest understory forbs and graminoids.

Drought stress can profoundly affect plant growth and physiological vitality, yet there is a notable scarcity of controlled drought experiments focused on herbaceous species of the forest understorey. In this study, we collected seeds from five forb and four graminoid species common in European temperate forests. Seeds were germinated under controlled glasshouse conditions and subjected to moderate drought stress for 5 weeks. We assessed biomass partitioning, stomatal and leaf morphology, leaf gas exchange, minimum leaf conductance (gmin), and chlorophyll fluorescence parameters. Comparison of the two ecological guilds revealed that graminoids had a higher R/S, improved WUE, greater carboxylation efficiency, and enhanced non-photochemical quenching under drought conditions compared to forbs. In contrast, forbs had significantly lower gmin, with higher total biomass and total leaf area. Despite these differences in morpho-physiological functional traits, both groups experienced a similar relative reduction in biomass after drought stress. Key predictors of biomass accumulation under drought included photochemical quenching, stomatal traits, total leaf area and gmin. A negative correlation between biomass and gmin suggests that plants with lower residual water loss after stomatal closure can accumulate more biomass under drought stress. Additionally, gmin was positively correlated with guard cell length, suggesting that larger stomata contribute to higher residual water loss. Contrasting strategies in morpho-physiological responses to drought define the differences between the two groups. In graminoids, drought resistance suggests greater emphasis on stress tolerance as a survival strategy. In contrast, forbs were able to maintain higher biomass and total leaf area, indicating a competitive strategy for maximizing resource acquisition.

Sensitive Hydraulic and Stomatal Decline in Extreme Drought Tolerant Species of California Ceanothus.

Identifying the physiological mechanisms by which plants are adapted to drought is critical to predict species responses to climate change. We measured the responses of leaf hydraulic and stomatal conductances (Kleaf and gs, respectively) to dehydration, and their association with anatomy, in seven species of California Ceanothus grown in a common garden, including some of the most drought-tolerant species in the semi-arid flora. We tested for matching of maximum hydraulic supply and demand and quantified the role of decline of Kleaf in driving stomatal closure. Across Ceanothus species, maximum Kleaf and gs were negatively correlated, and both Kleaf and gs showed steep declines with decreasing leaf water potential (i.e., a high sensitivity to dehydration). The leaf water potential at 50% decline in gs was linked with a low ratio of maximum hydraulic supply to demand (i.e., maximum Kleaf:gs). This sensitivity of gs, combined with low minimum epidermal conductance and water storage, could contribute to prolonged leaf survival under drought. The specialized anatomy of subg. Cerastes includes trichomous stomatal crypts and pronounced hypodermis, and was associated with higher water use efficiency and water storage. Combining our data with comparative literature of other California species, species of subg. Cerastes show traits associated with greater drought tolerance and reliance on leaf water storage relative to other California species. In addition to drought resistance mechanisms such as mechanical protection and resistance to embolism, drought avoidance mechanisms such as sensitive stomatal closure could contribute importantly to drought tolerance in dry-climate adapted species.

Green synthesis of boehmite-reinforced cashew gum/polypyrrole biopolymer blend for advanced biomaterials

Electrically conducting biopolymer blend nanocomposites based on different contents of boehmite (BHM) reinforced cashew gum (CG) /polypyrrole (PPy) blend is synthesized by an in situ polymerization technique using water as a green solvent. The resulting bio-blend nanocomposites underwent comprehensive analysis concerning their structural, morphology, thermal, and electrical properties, such as dielectric constant, dielectric loss, electric modulus, and AC conductivity. The Fourier transform infrared spectroscopy (FTIR) spectra revealed the presence of metal oxide stretching in the blended nanocomposite at 512 cm−1. Field emission scanning electron microscopy (FE-SEM) confirmed the attachment and uniform dispersion of BHM within the CG/PPy blend at 7 wt% loading, and beyond this loading, the nanoparticles get agglomerated in the biopolymer blend. The glass transition temperature and thermal stability of all the blended nanocomposites are higher than that of the pure CG/PPy blend and these thermal properties increase with the loading of nanoparticles. Conductivity experiments demonstrated that as the nanofiller content increases up to 7 wt%, there is a concurrent rise observed in AC conductivity, dielectric loss, and dielectric constant. There is a substantial difference of 1.21 Scm−1 between the maximum and minimum AC electrical conductivity, at 102 Hz. However, a decrease in electrical properties is observed at the highest loadings of BHM due to the agglomeration of nanoparticles in the polymer blend matrix. The lowest activation energy value (0.049 × 10−4 eV) is also exhibited by 7 wt% BHM nanocomposites. Furthermore, the electrical properties of both CG/PPy and CG/PPy/BHM nanocomposites exhibited a temperature-dependent behavior, progressively increasing until reaching maximum values. This study suggests that such bio-based polymer dielectrics could be promising materials for various applications, offering enhanced thermal and electrical properties through careful control of nanofiller content and dispersion.

Influence of different wire materials on the machining of Albromet W130 by WEDM

Wire Electrical Discharge Machining (WEDM) is an unconventional machining technology, widely spread in different sectors of many industries. The machining uses periodically repeating electrical impulses, which allows all materials with at least a minimum electrical conductivity to be machined. The machining tool is a thin wire that can be made of many different materials. Wire electrode material requirements vary from industry to industry. This study aimed to increase the efficiency of WEDM through an analysis of the influence of the type of wire material on the machining of Albromet W130 copper alloy. The analysis comprised a molybdenum, brass and a copper wire of a 0.25 mm diameter and a Box-Behnken design of experiment totalling 42 rounds. The design of experiment results analysis covered cutting speed, machined surfaces’ topography and morphology, and the subsurface layer condition. Furthermore, an analysis of the wire electrodes used in the experiment was carried out. The highest cutting speed was achieved using a copper wire and the lowest R a values were achieved in samples machined with a molybdenum wire.

Stomatal closure as a driver of minimum leaf conductance declines at high temperature and vapor pressure deficit in Quercus.

Rising global temperatures and vapor pressure deficits (VPDs) are increasing plant water demand and becoming major drivers of large-scale plant mortality. Controlling transient leaf water loss after stomatal closure (minimum stomatal conductance [gmin]) is recognized as a key trait determining how long plants survive during soil drought. Yet, substantial uncertainty remains regarding how gmin responds to elevated temperatures and VPD and the underlying mechanisms. We measured gmin in 24 Quercus species from temperate and Mediterranean climates to determine whether gmin was sensitive to a coupled temperature and VPD increase. We also explored mechanistic links to phenology, climate, evolutionary history, and leaf anatomy. We found that gmin in all species exhibited a nonlinear negative temperature and VPD dependence. At 25 °C (VPD = 2.2 kPa), gmin varied from 1.19 to 8.09 mmol m-2 s-1 across species but converged to 0.57 ± 0.06 mmol m-2 s-1 at 45 °C (VPD = 6.6 kPa). In a subset of species, the effect of temperature and VPD on gmin was reversible and linked to the degree of stomatal closure, which was greater at 45 °C than at 25 °C. Our results show that gmin is dependent on temperature and VPD, is highly conserved in Quercus species, and is linked to leaf anatomy and stomatal behavior.

Titanium ion effects on the spectroscopic and electrical characteristics of germano silicate lead alumino tellurite glass ceramics for dielectric applications

The Glass-ceramics 10GeO2-(55-x) SiO2–29PbO–5Al2O3–1TeO2 doped with varying amounts of TiO2 (0 < x < 5 mol %) were prepared through the process of melt quenching followed by heat treatment. X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Differential Thermal Analysis (DTA) were used to analyze these glass ceramics besides the usual spectral studies like optical absorption, Electron Paramagnetic Resonance (EPR), Fourier Transform Infrared Spectroscopy (FTIR) and Raman. These investigations demonstrated the existence of crystalline phases that comprise complexes of Ti4+ as well as Ti3+ ions that were dispersed randomly. Additionally, it is seen that Ti3+ ions, which are more prevalent as TiO2 concentration rises, take up the tetragonally deformed octahedral positions inside the network of glass ceramics. FTIR spectra of the synthesized samples provided information regarding the existence of different structural units in the glass ceramic matrix, which included SiO4, GeO4, GeO6, PbO4, PbO6, AlO6, TeO4, TeO3, TiO4, and TiO6. At 30 °C, the 3 mol % Ti-doped sample has a minimum conductivity of 1.623 × 10−9 S cm−1. Therefore, the dielectric and spectroscopic investigations suggest that glass ceramics containing 3 mol% of TiO2 are rigid and appropriate for dielectric applications.

Effect of Integrated Nutrient Management on Soil Nutrient Status in Garlic (Allium sativum L.)

An experiment was conducted during rabi season, 2021 to investigate the effect of integrated nutrient management on soil nutrient status in garlic. The study was structured around eighteen treatments with combinations of inorganic fertilizers, biofertilizers and organic manures like Jeevamrit and Beejamrit. The treatment T12 [(75 % RDF + 40 kg Sulphur/ha + Azotobacter + Phosphate Solubilizing Bacteria + FYM (25t/ha)] resulted in minimum soil pH (6.82) and electrical conductivity (0.181 dSm-1) as well as highest organic carbon (0.86 %), available Nitrogen (258.84 kg ha-1), Phosphorus (26.72 kg ha-1) contents. Further, the treatment T17 [(100 % RDF + FYM (25t/ha)] recorded maximum available Potassium (180.35 kg ha-1) and treatment T16 [(100 % RDF + 40 kg S/ha + FYM) recorded highest S (44.98 kg ha-1) contents. Thus, it can be concluded that integration of inorganic fertilizers with biofertilizers and organic manures helps in improving the soil nutrient status.

Thermal Transport and Thermal Polarization of Water in the Supercooled Regime.

The behavior of water in the deep supercooled regime has attracted significant interest, motivated by the hypothesis of the second critical point of water. Previous studies indicated the existence of a water anomaly, characterized by a minimum in the thermal conductivity of water. Here, we employ nonequilibrium molecular dynamics computer simulation and the TIP4P/2005 water force field to investigate the thermal conductivity of supercooled water targeting four different isobars, 1, 200, 700, and 1200 bar. We demonstrate using NEMD simulations the existence of minima in thermal conductivity associated with the maximum isothermal compressibility and the minimum speed of sound in water, hence establishing a firm connection with the second critical point of liquid water. Moreover, we demonstrate that thermal gradients polarize supercooled water with a thermal polarization coefficient of several mV/K. We explain the thermal polarization effect using a theoretical formulation introduced recently that connects the thermal polarization effect to the isobaric thermal expansion coefficient.

Study of the band alignment at the CZTS/ZrS2 interface based on first-principles calculation

Abstract To explore whether ZrS2 monolayer has the potential to become a buffer layer material for Cu2ZnSnS4 (CZTS) solar cells, the band arrangement of CZTS/ZrS2 heterojunction was predicted using density functional theory(DFT) first principles. In this paper, the hybrid functional HSE06 is used in all processes. The calculated results reveal a Type III band alignment at the CZTS/ZrS2 heterojunction interface, with the maximum valence band (VBM) of CZTS positioned 1.67 eV higher than the minimum conduction value (CBM) of ZrS2. The results indicate that the CZTS/ZrS2 interface may not be well-suited for utilization in solar cells, pointing towards potential areas for further investigation.

Optimizing the terrestrial ecosystem gross primary productivity using carbonyl sulfide (COS) within a two-leaf modeling framework

Abstract. Accurately modeling gross primary productivity (GPP) is of great importance for diagnosing terrestrial carbon–climate feedbacks. Process-based terrestrial ecosystem models are often subject to substantial uncertainties, primarily attributed to inadequately calibrated parameters. Recent research has identified carbonyl sulfide (COS) as a promising proxy of GPP due to the close linkage between leaf exchange of COS and carbon dioxide (CO2) through their shared pathway of stomatal diffusion. However, most of the current modeling approaches for COS and CO2 do not explicitly consider the vegetation structural impacts, i.e., the differences between the sunlit and shaded leaves in COS uptake. This study used ecosystem COS fluxes from seven sites to optimize GPP estimation across various ecosystems with the Biosphere-atmosphere Exchange Process Simulator (BEPS), which was further developed to simulate the canopy COS uptake under its state-of-the-art two-leaf framework. Our results demonstrated substantial improvement in GPP simulation across various ecosystems through the data assimilation of COS flux into the two-leaf model, with the ensemble mean of the root mean square error (RMSE) for simulated GPP reduced by 20.16 % to 64.12 %. Notably, we also shed light on the remarkable identifiability of key parameters within the BEPS model, including the maximum carboxylation rate of RuBisCO at 25 °C (Vcmax25), minimum stomatal conductance (bH2O), and leaf nitrogen content (Nleaf), despite intricate interactions among COS-related parameters. Furthermore, our global sensitivity analysis delineated both shared and disparate sensitivities of COS and GPP to model parameters and suggested the unique treatment of parameters for each site in COS and GPP modeling. In summary, our study deepened insights into the sensitivity, identifiability, and interactions of parameters related to COS and showcased the efficacy of COS in reducing uncertainty in GPP simulations.

Ideal two-dimensional electronic structure in bulk lead titanate for superior thermoelectrics

An ideal two-dimensional (2D) electronic structure is revealed in n-type tetragonal perovskite PbTiO3 through first-principle calculations. This opens exciting prospects for its applications in thermal-to-electrical energy conversion. The electronic structure is regarded as ideally 2D when it is highly dispersive only along two axes, while along the remaining axis, it is nearly non-dispersive with a bandwidth smaller than 1 meV – insignificant when compared to thermal energy above room temperature (i.e., kBT ≥ 25.9 meV). As a basis for comparison, the electronic structure of the cubic perovskite SrTiO3 is calculated. It is nonideal 2D with the bandwidth along the less dispersive axis larger than the thermal energy. The ideal 2D electronic structure in PbTiO3 leads to a 2D-like density of states, resembling a step function around the conduction minimum while for SrTiO3, the density of states remains 3D-like with a square-root energy dependence. Consequently, n-type PbTiO3 exhibits superior effective band degeneracy within the Fermi window compared to SrTiO3, even though PbTiO3 is nondegenerate at the conduction band minimum, while cubic SrTiO3 is three-fold degenerate. This demonstrates the important role of the ideality in the 2D electronic structure. The ab-initio results demonstrate the potential of PbTiO3 as a promising thermoelectric material.

Revitalising high voltage cable: Exploring effective repair methods and influential factors for buffer layer defects using conductive silicone rubber

AbstractIn recent years, the ablative discharge of the buffer layer in high‐voltage (HV) cross‐linked polyethylene (XLPE) cables has become a significant challenge for the operation and maintenance of power lines. However, there is a lack of effective methods to address buffer layer discharge defects. A practical approach is proposed to repair buffer layer defects and mitigate the associated discharge issues. To achieve this goal, the principles of repairing buffer layer defects are analysed by establishing an electrical network model that considers different contact states between the buffer layer and aluminium sheath. Based on this analysis, a method involving the injection of solidifiable rejuvenation fluid between the buffer layer and aluminium sheath is proposed to effectively suppress buffer layer discharge defects. Through simulation calculations, the minimum electrical conductivity and injection volume required to establish a reliable electrical connection between the buffer layer and aluminium sheath is determined. Additionally, a curable rejuvenation fluid containing conductive carbon black silicone rubber is prepared and analysed for its conductivity and flow properties at both the mesoscopic and macroscopic levels. Finally, a real cable office discharge test is conducted to compare the discharge behaviour of defective cables before and after repair. The results demonstrate that when the conductivity of the rejuvenation fluid exceeds 10−6 S/m, it effectively establishes a conductive channel between the insulation shield and aluminium sheath, thereby reducing the risk of discharge ablation. Furthermore, after injecting the rejuvenation fluid and completely covering the white mark defect, the discharge phenomenon in the buffer layer is significantly suppressed, leading to the restoration of its electrical performance.

CHARACTERISTICS OF MUTUAL ACTIVATION OF AN INTERGEL SYSTEM BASED ON HYDROGEL POLYMETHACRYL ACID AND POLY-4-VINYL PYRIDINE

The electrochemical properties of mutual activation of polymer networks as a result of remote interaction in an intergel system have been studied. An intergel system consisting of hydrogels of rare crosslinked polymethacrylic acid (hPMAA) and poly-4-vinylpyridine (hP4VP) was chosen as the object of study [1,2]. The purpose of the work is to study the mutual activation features of the intergel system of rare crosslinked hPMAA: hP4VP. The obtained results as the contact time of hydrogels with water increased, zones of maximum and minimum conductivity were observed at the highest points of initial conductivity for different ratios of hPMAA:hP4VP hydrogel systems. In the 6:0 ratio of hPMAA hydrogel, the specific conductivity of the aqueous medium reached its maximum value after one day, and the pH value of the medium decreased relatively to about 4.95. The swelling degree of hPMAA hydrogel was constant at 6:0 different time intervals. In this system, only one polymer, namely hPMAA showed that the hydrogel's water absorption capacity was limited. In the 5:1 ratio of the intergel system, the specific conductivity of the medium reached a high value, and the pH value decreased in the 5:1 ratio. After 2.5 hours of study, a decrease in the conductivity of the aqueous medium was observed at 4:2 hydrogel ratio. After 6 hours, the highest degree of swelling was maintained at 1:5 ratio. In the presence of hP4VP hydrogel at a ratio of 0:6, the pH of the medium increased from 5 to a maximum value of 6.6 within 24 hours. Conclusion. The electrochemical properties of hPMAA:hP4VP hydrogel system were studied by remote interaction. Based on the systematic work, we synthesized the required acidic hydrogel hPMAA:hP4VP and carried out various studies on their properties. To create an intergel system, the obtained hydrogels in seven different proportions were made into an intergel system and their interactions were studied using various physicochemical methods. As a result of the study, the remote interaction of hydrogels in the intergel system leads to conformational changes in their intercellular bonds which undergo additional swelling. As a result of mutual activation, the hydrogels move to a highly ionized state.

Thermal effect of the stack in a bipolar membrane electrodialysis: Mechanism, risk, size effect and salt effect

Thermal effect inevitably occurred in a bipolar membrane electrodialysis (BMED) stack impacts its energy efficiency and potentially damages non-metallic components. Up to now, thermal mechanism and impacts within a BMED stack remain incompletely understood. Thus, thermal mechanism and impacts within the stack were investigated using the validated equivalent circuit model of a BMED system. Its results revealed that currents/Joule effect in the main circuit were dominant compared to those in the external circuit. The proportion of Joule heat in the main circuit exceeds 99.00 %, while that in the external circuit was less than 1.00 %. Joule heat generated in the outermost slot of the maximum conductivity compartment was obvious, while that in any position of the main circuit within the minimum conductivity compartment was also significant. Thermal impacts of non-metallic components were affected by the heat transfer of solution thermal effect. Besides, these effects which included current distribution, Joule effect, and thermal risk, were mainly affected by the size of the element at spacer, and the conductance provided by the salt and its products. Larger size of slots/ducts at spacer reduced the heat transfer efficiency at their location, while that of main channel enhanced the heat transfer efficiency between membranes and solution. Low conductivity salts and corresponding products pose a greater thermal risk for BMED stack. Meanwhile, these effects would be aggravated from the lab- to large-scale BMED stack. These findings can enhance the comprehension of the involved processes for optimizing BMED technique, thereby accelerating its development.

Pinpointing the causal influences of stomatal anatomy and behavior on minimum, operational, and maximum leaf surface conductance.

Leaf surface conductance to water vapor and CO2 across the epidermis (gleaf) strongly determines the rates of gas exchange. Thus, clarifying the drivers of gleaf has important implications for resolving the mechanisms of photosynthetic productivity and leaf and plant responses and tolerance to drought. It is well recognized that gleaf is a function of the conductances of the stomata (gs) and of the epidermis + cuticle (gec). Yet, controversies have arisen around the relative roles of stomatal density (d) and size (s), fractional stomatal opening (α; aperture relative to maximum), and gec in determining gleaf. Resolving the importance of these drivers is critical across the range of leaf surface conductances, from strong stomatal closure under drought (gleaf,min), to typical opening for photosynthesis (gleaf,op), to maximum achievable opening (gleaf,max). We derived equations and analyzed a compiled database of published and measured data for approximately 200 species and genotypes. On average, within and across species, higher gleaf,min was determined 10 times more strongly by α and gec than by d and negligibly by s; higher gleaf,op was determined approximately equally by α (47%) and by stomatal anatomy (45% by d and 8% by s), and negligibly by gec; and higher gleaf,max was determined entirely by d. These findings clarify how diversity in stomatal functioning arises from multiple structural and physiological causes with importance shifting with context. The rising importance of d relative to α, from gleaf,min to gleaf,op, enables even species with low gleaf,min, which can retain leaves through drought, to possess high d and thereby achieve rapid gas exchange in periods of high water availability.

Transport properties of the resonant tunneling structures based on the pseudospin-1 Dirac–Weyl fermions

Transmission, conductivity, and shot noise are investigated in multi-barrier resonant tunneling structures based on the pseudospin-1 Dirac–Weyl model. Super Klein tunneling, perfect transmission plateau, and resonant tunneling collectively contribute to the transport properties. While resonant tunneling occurs when the energy of the passing quasiparticle coincides with the discrete quasibound energy level of the multi-barrier structure and is widely observed in parabolic and Dirac-cone-shape dispersive materials, super Klein tunneling and perfect transmission plateau are unique in pseudospin-1 systems and barrier-structure independent. As a result, the conductivity and shot noise in pseudospin-1 resonant-tunneling multi-barrier structures demonstrate remarkably different properties from their counterparts of both parabolic-dispersion semiconductors and pseudospin-1/2 Dirac–Weyl materials, typically graphene. It is found that the zero conductivity minimum remains for multi-barrier structures and the relative shot noise indicated by the Fano factor in the three-barrier system is larger than that in the double-barrier system when the Klein tunneling effect weakens.

Effect of polymer concentration and cross-linking density on the microstructure and properties of polyimide aerogels

Polyimide aerogels display excellent mechanical strength, high thermal stability, low thermal conductivity, and outstanding dielectric properties. Typically, the synthesis of polyimide aerogels involves the polycondensation of dianhydride and diamine into poly(amic acid) (PAA) oligomers, which are then cross-linked and chemically imidized into polyimide. The stoichiometry of dianhydride and diamine determines the number of repeat units and length of the PAA oligomers, which in turn determines the cross-linking density. Despite the critical role of polymer concentration and number of repeating units in determining the microstructure and properties of polyimide aerogels, few detailed studies exist on these two parameters. Here, we synthesized and characterized 16 polyimide aerogel formulations from the common monomers biphenyl-3,3′,4,4′-tetracarboxylic dianhydride (BPDA) and 4,4′-oxydianiline (ODA), with different repeat units (n = 5, 15, 30, 45) and total polymer concentrations (4, 7, 10, 13 wt%). An increased polymer concentration accelerated gelation and enhanced the mechanical performance of aerogels, but surprisingly, it also led to higher volumetric shrinkage during aging, solvent exchange, and supercritical drying (SCD). Specific surface areas (SSAs) reached a maximum at intermediate polymer concentrations. A shorter oligomer chain length, i.e., a higher cross-linking density, led to moderately higher SSAs (between 320 and 400 m2/g) and reduced shrinkage, resulting in lower densities for a given polymer concentration. The density dependence of the thermal conductivity exhibits a pronounced U-shaped curve with a minimum in thermal conductivity of 21–23 mW/(m·K) between 0.080 and 0.120 g/cm3, with somewhat lower values for more highly cross-linked aerogels. This systematic study of polyimide aerogels forms the basis for designing polyimide aerogels with tailored properties for targeted applications.Graphical

The combined effect of diffuse radiation and leaf wetness on functional traits and transpiration efficiency on a cloud forest species.

Cloud forests are unique biomes that thrive in foggy environments for a substantial part of the season. Fog in cloud forests plays two critical roles: it reduces incoming radiation and creates a humid environment, leading to the wetting of the canopy. This paper aims to investigate the combined effect of both radiation and wetness on Myrica faya Wilbur-a cloud forest species present in subtropical regions-both directly in plants and through simulations. Experiments consisted of a controlled environment with two levels of radiation and leaf wetness: low radiation/wet conditions, and high radiation/no-wetness; and three treatments: continuous low radiation and wetness, continuous high radiation and no wetness and alternate high low radiation and alternate wetness. The results revealed that a combination of low radiation and leaf wetness significantly improves leaf stomata conductance and increases the specific leaf area (SLA). Changes in SLA were driven by leaf size changes. However, the minimum leaf conductance (gmin) did not respond to any of the treatments. The simulations focused on exploring the impact of radiation and canopy wetness on transpiration efficiency (TE), i.e. the ratio between photosynthesis (An) and transpiration (Tc). The simulations demonstrated that TE increased exponentially as the canopy was gradually wetted, regardless of the radiation environment. This increase in TE results from Tc approaching zero while An maintains positive values. Overall, this study provides an integrated understanding of how fog alters M. faya functioning and, potentially, other cloud forest tree species.

Plasticity and implications of water-use traits in contrasting tropical tree species under climate change.

Plants face a trade-off between hydraulic safety and growth, leading to a range of water-use strategies in different species. However, little is known about such strategies in tropical trees and whether different water-use traits can acclimate to warming. We studied five water-use traits in 20 tropical tree species grown at three different altitudes in Rwanda (RwandaTREE): stomatal conductance (gs), leaf minimum conductance (gmin), plant hydraulic conductance (Kplant), leaf osmotic potential (ψo) and net defoliation during drought. We also explored the links between these traits and growth and mortality data. Late successional (LS) species had low Kplant, gs and gmin and, thus, low water loss, while low ψo helped improve leaf water status during drought. Early successional (ES) species, on the contrary, used more water during both moist and dry conditions and exhibited pronounced drought defoliation. The ES strategy was associated with lower mortality and more pronounced growth enhancement at the warmer sites compared to LS species. While Kplant and gmin showed downward acclimation in warmer climates, ψo did not acclimate and gs measured at prevailing temperature did not change. Due to distinctly different water use strategies between successional groups, ES species may be better equipped for a warmer climate as long as defoliation can bridge drought periods.