Experimental Study on Heat Conduction and Water Migration of Composite Bentonite Samples.

The joints of buffer material composite blocks as potential weak parts in the engineering barrier system of a high-level radioactive waste (HLW) repository must be studied in depth. Therefore, a laboratory experiment device suitable for unsaturated composite bentonite samples was developed. The evolution of temperature and volumetric water content at different locations of Gaomiaozi (GMZ) composite bentonite samples with time before and after simulated water inflow was measured by the experiment device. According to the experimental results, the thermal conductivity and hydraulic conductivity of the joint location after healing of the composite bentonite samples were obtained. The experimental results show that the change in the internal temperature of the composite bentonite samples is mainly affected by the temperature boundary and that the change in the internal water has little effect on it. In a short period of time, the loading of hydraulic boundary conditions only makes the volumetric water content of the soil near the hydraulic boundary increase significantly but has little effect on other locations. And, affected by the temperature boundary, the volumetric water content of the soil near the temperature boundary gradually decreases with time. The process of hydration swelling of the composite bentonite sample is accompanied by the adjustment of stress. The composite bentonite samples are continuously squeezed to the joint area after hydration swelling, the whole composite samples are generally homogenized, and the joints between the composite bentonite samples tend to heal. The thermal conductivity and permeability of the joint location after healing can meet the requirements of the engineering barrier of the HLW repository.

Examining the crucial role of polysaccharide polymers in influencing soil hydraulic conductivity: A comprehensive review.

This paper examines the impact of biopolymers on hydraulic conductivity of soils, representing a key parameter for many environmental and geotechnical applications. The complexity of this relationship is compounded by researchers employing diverse approaches and presentation formats, resulting in apparent inconsistencies. However, this review intends to address these challenges by identifying various categories of biopolymers that influence the hydraulic conductivity and discuss the recent research findings. By elucidating the diverse impacts of these biopolymers on hydraulic conductivity, this review offers valuable insights into the historical development and origins of soils treated with hydraulic conductivity modifying biopolymers. It not only traces the evolution and background of these treatments but also identifies areas of conflicting evidence and ongoing debate in the field. In the overall, this review is an essential resource for engineers and researchers working in the geotechnical field, by providing a nuanced understanding of the intricate dynamics between biopolymers and soil hydraulic conductivity. The newly developed multi-variable functions can be systematically utilized to predict the hydraulic conductivity of soils treated with biopolymers, commonly encountered in various geotechnical and environmental engineering applications.

Mechanical properties of aeolian sand cemented via microbially induced calcite precipitation (MICP).

The cementation of desert aeolian sand is a key method to control land desertification and dust storms, so an economical, green and durable process to reach the binding between sand grains needs to be searched. The method based on the microbially induced calcite precipitation (MICP) appeared in recent years as a promising process that proved its efficiency. The feasibility of the MICP technique to treat aeolian sand composed by low clay content, fine particles, low water content and characterized by weak permeability was demonstrated in the present paper. The effects of initial dry density, cementation number and curing time on the permeability and strength of MICP-treated aeolian sand were investigated using permeability tests and unconfined compressive strength (UCS) tests. The microstructure of aeolian sand was observed by scanning electron microscopy (SEM) tests and X-ray diffraction (XRD), aiming to reveal the solidification principle of MICP. The tests result indicated that when the initial dry density and the cementation number rose, the hydraulic conductivity of aeolian sand decreased while the mechanical strength given by UCS values improved. When the initial dry density was 1.65 g/cm3, the curing time was 3 h and the cementation number reached 20, the hydraulic conductivity and UCS reached 0.00151 cm/s and 1050.30 kPa, respectively. With increasing curing time, the hydraulic conductivity first decreased, followed by an increase, while the UCS exhibited an up and then a downtrend. Furthermore, the correlation between UCS values and the CaCO3 content reached a high R2 value equal to 0.912, which confirmed that the cementation occurred in sandy material and governed the soil strengthening. Indeed, the calcium carbonate crystals observed by SEM and XRD enhanced the friction between particles when they wrapped around the sand grains surface, while carbonates reduced the soil permeability when filling the pores and sticking the sand particles together. Finally, the theoretical and scientific knowledge brought by the present study should help in managing sand in desert areas.

Interception behaviors of mixed chlorinated hydrocarbons in groundwater by DDAC-amended LPBs: Control mechanism and CFD simulation.

Low permeability barrier has emerged as a promising, cost-effective technology for anti-seepage and pollution mitigation in geotechnical engineering. However, its efficacy in organic pollution sites, particularly those contaminated with chlorinated hydrocarbons (CHCs) pales in comparison to its performance in areas contaminated by heavy metals. In order to rectify this deficiency, a novel bentonite backfill, modified with dihexadecyl dimethyl ammonium chloride (DDAC) and designated as DDAC-LPB, is proposed for use in low permeability barriers to contain CHCs in groundwater at contaminated sites. A series of rigid-wall permeability tests, mechanical properties tests, and diffusion tests were conducted to investigate the impact of CHCs solution on hydraulic conductivity, unconfined compression strength and adsorption properties of the LPB, respectively. The results reveal that LPB containing 10 % DDAC modified bentonite exhibits excellent impermeability and mechanical workability, with a 2-5 fold increase in adsorption capacity, primarily driven by the hydrophobic interaction between CHCs and DDAC. Moreover, this study has innovatively applied computational fluid dynamics simulation to the field of solute transport modeling to evaluate the performance of DDAC-LPB in containing CHCs within lateral flowing groundwater. This novel approach was benchmarked against the widely embraced convection-diffusion equation modeling method, demonstrating a significant improvement in predictive accuracy. In a typical field scenario, the breakthrough time for CHCs using the DDAC-LPB technique ranged from 25.3 to 25.5 years, with a barrier thickness of 1 m. This duration satisfactorily aligns with the expected service life of real-world projects. Overall, the DDAC-LPB has demonstrated superior performance and practical applicability in enhancing the containment of CHCs in contaminated groundwater.

Mixing oak and pine trees in Mediterranean forests increases aboveground hydraulic dysfunctions.

Increasing tree species diversity in Mediterranean forests could reduce drought-induced hydraulic impairments through improved microclimate and reduced competition for water. However, it remains unclear if and how species diversity modulates tree hydraulic functions and how impacts may shift during the growing season. Using unmanaged Mediterranean forest stands composed of one (i.e., monospecific) or four (i.e., multispecific) tree species, we examined the seasonal dynamics of in-situ hydraulic traits (predawn and midday leaf water potential - Ψpd and Ψmd, xylem- and leaf-specific hydraulic conductivity - KS and KL, percentage loss of conductivity - PLC, specific leaf area - SLA, and Huber value - HV) in four co-existing Pinus and Quercus species over two years. We mainly observed adverse impacts of species diversity with lower Ψpd, Ψmd, KS, KL, and higher PLC in multispecific compared to monospecific stands, especially for the two pines. These impacts were observed all along the growing season but were stronger during the driest periods of the summer. Beneficial impacts of diversity were rare and only occured for oaks (Q. faginea) after prolonged and intense water stress. Our findings reveal that mixing oaks and pines could mainly enhance hydraulic impairments for all species during the dry season, suggesting a potential decline in mixed Mediterranean forests under future climate.

Growing-Season Precipitation Is a Key Driver of Plant Leaf Area to Sapwood Area Ratio at the Global Scale.

Leaf area to sapwood area ratio (AL/AS) influences carbon sequestration, community composition, and ecosystem functioning in terrestrial vegetation and is closely related to leaf economics and hydraulics. However, critical predictors of AL/AS are not well understood. We compiled an AL/AS data set with 1612 species-site combinations (1137 species from 285 sites worldwide) from our field experiments and published literature. We found the global mean AL/AS to be 0.63 m2 cm-2, with its variation largely driven by growing-season precipitation (Pgs), which accounted for 18% of the variation in AL/AS. Species in tropical rainforests exhibited the highest AL/AS (0.82 m2 cm-2), whereas desert species showed the lowest AL/AS (0.16 m2 cm-2). Soil factors such as soil nitrogen and soil organic carbon exhibited positive effects on AL/AS, whereas soil pH was negatively correlated with AL/AS. Tree density accounted for 7% of the variation in AL/AS. All biotic and abiotic predictors collectively explained up to 45% of the variation in AL/AS. Additionally, AL/AS was positively correlated to the net primary productivity (NPP) of the ecosystem. Our study provides insights into the driving factors of AL/AS at the global scale and highlights the importance of AL/AS in ecosystem productivity. Given that Pgs is the most critical driver of AL/AS, alterations in global precipitation belts, particularly seasonal precipitation, may induce changes in plant leaf area on the branches.

Transport and retention mechanisms of highly suspended biochar in aquifer media.

Biochar-based in-situ reaction zones are promising methods for groundwater remediation. However, the transport and retention of biochar in aquifer media remain unclear. Herein, biochar with high suspensibility was developed through nitrogen doping. A linear regression was used to analyze the relationship between particle size, concentration, time, and suspension rate. Seepage column experiments were conducted to investigate the transport and retention mechanisms of biochar in the aquifer medium. The ratio of biochar particle size (dp) to medium particle size (Dp) affected the permeability coefficient. At a 3.0 g/L injected concentration, hydraulic conductivity decreased within 3.3 × 10-3 ≤ dp/Dp ≤ 8.4 × 10-3. Within 9.7 × 10-3 ≤ dp/Dp ≤ 1.9 × 10-2, hydraulic conductivity first increased and then decreased. Within 2.5 × 10-2 ≤ dp/Dp ≤ 5.7 × 10-2, hydraulic conductivity slightly increased and then stabilized. This study confirms that nitrogen-doped biochar is an excellent remediation material for in-situ reaction zone.

Contaminant mass discharge estimation of a sulfonamide plume by use of hydraulic profiling tool (HPT) and fluorescence techniques.

The contaminant mass discharge is a relevant metric to evaluate the risk that a groundwater plume poses to water resources. However, this assessment is often vitiated by a high uncertainty inherent to the assessment method and often limited number of measurement points to carry out the assessment. Direct-Push techniques in combination with profiling tools and dedicated sampling can be an interesting alternative to increase the measurement point density and hence reduce the mass discharge uncertainty. The main objective of our study was to assess if DP logging and sampling could be employed to get a reasonable estimate of contaminant mass discharge in a large sulfonamide contaminant plume (> 1500 m wide), compared to a more traditional approach based on monitoring wells. To do so, an Hydraulic Profiling Tool (HPT) logging with a dedicated site calibration was used to estimate the hydraulic conductivity field. The sulfonamide concentrations were inferred from the compound fluorescence properties measured by laboratory spectrofluorometry (λEx / λEm = 255/340 nm) and a dedicated log-log linear regression model. Our results show that HPT-derived hydraulic conductivity values are in good agreement with the monitoring well results, and within the order of magnitude reported in similar studies or indirect geophysical techniques. Fluorescence appears as a powerful proxy for the sulfonamide concentration levels. Ultimately, the contaminant mass discharge estimate from HPT and fluorescence techniques lies within a factor 2 from the estimate by monitoring wells, with 549 [274-668] and 776 [695-879] kg/yr respectively. Overall, this study highlights that DP logging tools combined with indirect methods (correlation with fluorescence) could provide a relevant contaminant mass discharge estimate for some optically active substances, given that a proper calibration phase is carried out.

Hydraulic mechanism of limiting growth and maintaining survival of desert shrubs in arid habitats.

The growth and survival of woody plant species is mainly driven by evolutionary and environmental factors. However, little is known about the hydraulic mechanisms that respond to growth limitation and enable desert shrub survival in arid habitats. To shed light on these hydraulic mechanisms, 9-, 31-, and 56-year-old Caragana korshinskii plants that had been grown under different soil water conditions at the southeast edge of the Tengger Desert, Ningxia, China were used in this study. The growth of C. korshinskii was mainly limited by soil water rather than shrub age in non-watered habitats, which indicated the importance of maintaining shrub survival prior to growth under drought. Meanwhile, higher vessel density, narrower vessels and lower xylem hydraulic conductivity indicated that shrubs enhanced hydraulic safety and reduced their hydraulic efficiency in arid conditions. Importantly, xylem hydraulic conductivity mediated by variation in xylem hydraulic architecture regulated photosynthetic carbon assimilation and growth of C. korshinskii. Our study highlights that the synergistic variation in xylem hydraulic safety and hydraulic efficiency is the hydraulic mechanism limiting growth and maintaining survival of C. korshinskii under drought, providing insights into the strategies for growth and survival of desert shrubs in arid habitats.

A simple model for predicting the hydraulic conductivity of MICP-treated sand.

In this research paper, we introduce a novel and sustainable approach for forecasting the hydraulic conductivity of sand layers subjected to microbial-induced carbonate precipitation (MICP) to mitigate the diffusion of toxic pollutants. The proposed model uniquely integrates the impact of varying CaCO3 contents on the void ratio and estimates the average particle size of CaCO3 crystals through scanning electron microscopy (SEM) analysis. By incorporating these parameters into the K-C equation, a simplified predictive model is formulated for assessing the hydraulic conductivity of MICP-treated sand layers. The model's effectiveness is validated through comparison with experimental data and alternative models. The outcomes demonstrate a substantial reduction in hydraulic conductivity, with a decrease ranging between 93 and 97% in the initial assessment and a decrease between 67 and 92% in the follow-up assessment, both at 10% CaCO3 content. Notably, the hydraulic conductivity shows an initial sharp decrease followed by stabilization. These findings provide valuable insights into improving the prediction of hydraulic conductivity in MICP-treated sand layers, promoting a sustainable method for preventing pollution dispersion.

Long-term observations on the hydraulic performance of a combined capillary barrier-methane oxidation landfill cover system.

This study quantifies the field hydraulic performance of a dual-functionality landfill cover, combining microbial methane oxidation with water diversion using a capillary barrier. The investigated 500 m2 test field, constructed on a landfill in the Netherlands, consisted of a cover soil optimised for methane oxidation, underlain by a sandy capillary layer and a gravelly capillary block. Outflows from these layers were measured between 2009 and 2023. Average precipitation was 848 mm/a, evapotranspiration, diverted infiltration and breakthrough amounted to 504 (59.4 %), 282 (33.3 %) and 62 (7.3 %) mm/a, respectively. On average, the capillary barrier diverted 82 % of the inflow into the capillary layer. Breakthrough occurred mainly from October to March when evapotranspiration was low and the maximum water storage capacity of the cover soil was reached. During this period, inflow into the capillary barrier exceeded its diversion capacity, caused by the relatively high hydraulic conductivity of the cover soil due to its optimisation for gas transport. The diversion capacity declined drastically in the year after construction and increased again afterwards. This was attributed to suffusion of sand from the capillary layer into the capillary block and subsequent washout to greater depths or the influence of iron precipitates at the bottom of the capillary layer. The effect of a more finely grained methane oxidation layer on the hydraulic and methane oxidation performance should be investigated further. These measures could further improve the combined performance of the dual functionality landfill cover system under the given conditions of a temperate climate.

Hydrological response and crack resistance of polypropylene-fiber reinforced compacted steel slag-bentonite mixtures under wetting-drying cycles.

Desiccation-induced cracks in a compacted clay liner significantly deteriorate the hydraulic barrier performance of landfill covers. The present study explores the effects of polypropylene (PP) fiber reinforcement on the hydrological response and crack resistance of compacted steel slag (SS; 90 wt%) - bentonite (10 wt%) mixtures under drying and wetting cycles. Comprehensive tests were conducted to explore the impact of different fiber lengths (6-12 mm) and contents (0-0.4 % wt.%), including hydraulic conductivity tests for measuring the saturated hydraulic conductivity (ks), unconfined-penetration tests for measuring the tensile strength, small-sized plate tests for quantifying crack development, and large-sized bucket tests for studying the hydrological response and crack characteristics. Higher fiber contents and longer fiber lengths increased the ks-value of the specimens. For a 0.3 % fiber content, the tensile strength peaked for the 9-mm fiber. Consistently, the specimen reinforced with the 9-mm fibers exhibited significantly fewer cracks than those reinforced with the 6-mm and 12-mm fibers. It was because the 6-mm fibers had a shorter anchorage length, while the 12-mm fibers tended to agglomerate. The large-sized bucket tests showed that fiber reinforcement limited crack development significantly under wetting and drying cycles, reducing the rainfall infiltration by 40 % and enhancing the soil water retention capacity. Finally, a 0.3 wt% of 9-mm PP was recommended to reinforce the compacted SS-bentonite mixtures.

Root Influences Rhizosphere Hydraulic Properties through Soil Organic Carbon and Microbial Activity.

Processes of water retention and movement and the hydraulic conductivity are altered in the rhizosphere. The aim of this study was to investigate the physical-hydric properties of soil aggregates in the rhizosphere of annual ryegrass (Lolium multiflorum) cropped in a Kandiudalfic Eutrudox, taking into account aspects related to soil aggregate stability. Soil aggregates from rhizosphere soil (RZS) and soil between plant rows (SBP) were used to determine soil water retention curves (SWRCs) and saturated hydraulic conductivity (Ksat). In addition, properties related to soil aggregate stability, such as water-dispersible clay, soil organic carbon (SOC), and microbial activity, were also assessed. The higher microbial activity observed in the RZS was facilitated by increased SOC and microbial activity, resulting in improved soil aggregation (less water-dispersible clay). For nearly all measured matric potentials, RZS had a higher water content than SBP. This was attributed to the stability of aggregates, increase in SOC content, and the root exudates, which improved soil water retention. The increase in total porosity in RZS was associated with improved soil aggregation, which prevents deterioration of the soil pore space and results in higher Ksat and hydraulic conductivity as a function of the effective relative saturation in RZS compared to SBP.

Influence of vegetation pattern and aridity on soil properties related soil available water in the Mediterranean regions.

Grassland ecology is deteriorating along with a fall in biodiversity and ecosystem services as a result of climate change in the Mediterranean regions. Understanding the mechanism of feedback between soil properties related to available water and increasing aridity is a key component of preserving grassland ecosystems. Structural equation modelling was used to explore a deep understanding of the underlying mechanisms of the feedback between soil properties related to available water and increasing aridity. In most cases, vegetation patches had significantly higher soil properties related to available water than inter-patches. Compared to inter-patches, the fine fractions of silt and clay content, soil organic carbon, saturated hydraulic conductivity, and available water under vegetation patches increased by 3.79%-7.64%, 31.08%-37.64%, 96.65%-141.14%, and 2.63%-9.21%, respectively, under limestone and mica schist lithologies. The fine fractions of silt and clay content, soil organic carbon, and available water were more responsive to the aridity index than the vegetation patch, while saturated hydraulic conductivity was more responsive to the vegetation patch than the aridity index. These complex relationships demonstrated that the available water was significantly positively affected by the vegetation pattern (0.09) and the aridity index (0.21-0.38). Soil texture had a significantly direct effect (0.43-0.53) on available water. Increasing aridity would strengthen the contrast in soil water availability while weakening the contrast in saturated hydraulic conductivity between vegetation patches and inter-patches. Available water was controlled by many aspects except vegetation pattern and aridity index. Understanding these relationships helped in predicting and mitigating the impacts of climate change on soil properties related to available water. The study offered fresh perspectives on the mechanism of vegetation pattern and aridity index on the various soil properties related to available water in arid and semiarid grasslands ecosystems under climate change.

Polystyrene nanoplastics induce cell type-dependent secondary wall reinforcement in rice (Oryza sativa) roots and reduce root hydraulic conductivity.

Nanoplastics (NPs) have been demonstrated the ability to penetrate plant roots and cause stress. However, the extent of NPs penetration into various root tissues and the corresponding plant defense mechanisms remain unclear. This study examined the penetration and accumulation patterns of polystyrene nanoplastics (PS-NPs) in different cell types within rice roots, and explored how the roots quickly modify their cell wall structure in response. The findings showed that fully developed sclerenchyma cells in rice roots effectively prevented the invasion of PS-NPs. Meanwhile, PS-NPs triggered the accumulation of lignin and suberin in specific cells such as the exodermis, sclerenchyma, and xylem vessels. PS-NPs at a concentration of 50 mg L-1 increased cell wall thickness by 18.6 %, 21.1 %, and 22.4 % in epidermis, exodermis, and sclerenchyma cells, respectively, and decreased root hydraulic conductivity by 14.8 %. qPCR analysis revealed that PS-NPs influenced the cell wall synthesis pathway, promoting the deposition of lignin and suberin monomers on the secondary wall through the up-regulation of genes such as OsLAC and OsABCG. These results demonstrate that PS-NPs can induce cell type-specific strengthening of secondary walls and barrier formation in rice roots, suggesting the potential role of plant secondary wall development in mitigating NPs contamination risks in crops.

Linkages between stem vulnerability curves and tree demography and their implications for plant physiological modeling.

Vulnerability curves (VCs) have been measured extensively to describe the differences in plant vulnerability to cavitation. Although the roles of hydraulic conductivity (Ks,max) and hydraulic safety (P50, embolism resistance), both of which are parameters of VCs ('sigmoidal' type), in tree demography have been evaluated across different forests, the direct linkages between VCs and tree demography are rarely explored. In this study, we combined measured VCs and plot data of 16 tree species in Panamanian seasonal tropical forests to investigate the connections between VCs and tree mortality, recruitment and growth. We found that the mortality and recruitment rates of evergreen species were most significantly positively correlated with P50. However, the mortality and recruitment rates of deciduous species only exhibited significant positive correlations with parameter a, which describes the steepness of VCs and indicates the sensitivity of conductivity loss with water potential decline, but is often neglected. These differences among evergreen and deciduous species may contribute to the poor performance of existing quantitative relationships (such as the fitting relationships for all 16 species) in capturing tree mortality and recruitment dynamics. Additionally, evergreen species presented a significant positive relationship between relative growth rate (RGR) and Ks,max, while deciduous species did not display such relationship. The RGR of both evergreen and deciduous species also displayed no significant correlations with P50 and a. Further analysis demonstrated that species with steeper VCs tended to have high mortality and recruitment rates, while species with flatter VCs were usually those with low mortality and recruitment rates. Our results highlight the important role of parameter a in tree demography, especially for deciduous species. Given that VC is a key component of plant hydraulic models, integrating measured VC rather than optimizing its parameters will help improve the ability to simulate and predict forest response to water availability.

The weighted multi-scale connections networks for macrodispersivity estimation.

Macrodispersivity is critical for predicting solute behaviors with dispersive transport models. Conventional methods of estimating macrodispersivity usually need to solve flow equations and are time-consuming. Convolutional neural networks (CNN) have recently been proven capable of efficiently mapping the hydraulic conductivity field and macrodispersivity. However, the mapping accuracy still needs further improvement. In this paper, we present a new network shortcut connection style called weighted multi-scale connections (WMC) for convolutional neural networks to improve mapping accuracy. We provide empirical evidence showing that the WMC can improve the performance of CNN in macrodispersivity estimation by implementing the WMC in CNNs (CNN without short-cut connections, ResNet, and DenseNet), and evaluating them on datasets of macrodispersivity estimation. For the CNN without short-cut connections, the WMC can improve the estimating R2 by at least 3% on three datasets of conductivity fields. For ResNet18, the WMC improved the estimated R2 by an average of 2.5% on all three datasets. For ResNet34, the WMC improved the estimated R2 by an average of 5.6%. For ResNet50, the WMC improved the estimated R2 by an average of 16%. For ResNet101, the WMC improved the estimating R2 by an average of 30%. For DenseNets, the improved estimated R2 ranges from 0.5% to 5%. The WMC can strengthen feature propagation of different sizes and alleviate the vanishing-gradient issue. Moreover, it can be implemented to any CNN with down-sampling layers or blocks.

Geotechnical performance of black cotton clay in the presence of lead and cadmium solutions for geoenvironmental application.

The usage of bentonites and sand-bentonite mixtures as liners has become prevalent due to their low permeability. However, these materials are scarce and prohibitively expensive in India. Black cotton clay (BCC) was chosen as an alternative clay liner for this research due to its abundance in India and its mineralogical composition. Since heavy metals accumulation in municipal landfills is a rising issue with devastating effects on the ecosystem and human health, in this investigation, two heavy metals (lead and cadmium) were intended as permeants at three different concentrations (100, 500, and 1000 ppm) to imitate the impact of heavy metal leachate on BCC. The essential index and engineering properties of BCC were evaluated and compared under these two permeants from the liner perspective. Experimental results revealed that the free swell index, Atterberg limits, swelling and swelling pressures were reduced for a rise in concentration irrespective of metal type. However, this reduction was more with cadmium permeants compared to lead. The measured swelling data was compared with predicted swelling data using a rectangular hyperbola model, and a good correlation was achieved. The hydraulic conductivity (k) and unconfined compressive strength (UCS) values were increased for a rise in concentration with both metal permeants. At 1000 ppm concentration, the k values were raised to 3.5 and 6.7 times, and UCS values were enhanced by 8.3 and 5.5% for lead and cadmium permeants, respectively. At high concentrations, field emission scanning electron microscopy (FESEM) results showed the formation of huge voids and aggregation.

Canopy Architecture and Sun Exposure Influence Berry Cluster-Water Relations in the Grapevine Variety Muscat of Alexandria.

Climate-change-related increases in the frequency and intensity of heatwaves affect viticulture, leading to losses in yield and grape quality. We assessed whether canopy-architecture manipulation mitigates the effects of summer stress in a Mediterranean vineyard. The Vitis vinifera L variety Muscat of Alexandria plants were monitored during 2019-2020. Two canopy shoot-positioning treatments were applied: vertical shoot positioning (VSP) and modulated shoot positioning (MSP). In MSP, the west-side upper foliage was released to promote partial shoot leaning, shading the clusters. Clusters were sampled at pea size (PS), veraison (VER), and full maturation (FM). Measurements included rachis anatomy and hydraulic conductance (Kh) and aquaporins (AQP) and stress-related genes expression in cluster tissues. The results show significant seasonal and interannual differences in Kh and vascular anatomy. At VER, the Kh of the rachis and rachis+pedicel and the xylem diameter decreased but were unaffected by treatments. The phloem-xylem ratio was either increased (2019) or reduced (2020) in MSP compared to VSP. Most AQPs were down-regulated at FM in pedicels and up-regulated at VER in pulp. A potential maturation shift in MSP was observed and confirmed by the up-regulation of several stress-related genes in all tissues. The study pinpoints the role of canopy architecture in berry-water relations and stress response during ripening.

Coordination between degree of isohydricity and depth of root water uptake in temperate tree species.

In an increasingly dry environment, it is crucial to understand how tree species use soil water and cope with drought. However, there is still a knowledge gap regarding the relationships between species-specific stomatal behaviour, spatial root distribution, and root water uptake (RWU) dynamics. Our study aimed to investigate above- and below-ground aspects of water use during soil drying periods in four temperate tree species that differ in stomatal behaviour: two isohydric tracheid-bearing conifers, Scots pine and Norway spruce, and two more anisohydric deciduous species, the diffuse-porous European beech, and the ring-porous Downy oak. From 2015 to 2020, soil-tree-atmosphere-continuum parameters were measured for each species in monospecific forests where trees had no access to groundwater. The hourly time series included data on air temperature, vapor pressure deficit, soil water potential, soil hydraulic conductivity, and RWU to a depth of 2 m. Analysis of drought responses included data on stem radius, leaf water potential, estimated osmotically active compounds, and drought damage. Our study reveals an inherent coordination between stomatal regulation, fine root distribution and water uptake. Compared to conifers, the more anisohydric water use of oak and beech was associated with less strict stomatal closure, greater investment in deep roots, four times higher maximum RWU, a shift of RWU to deeper soil layers as the topsoil dried, and a more pronounced soil drying below 1 m depth. Soil hydraulic conductivity started to limit RWU when values fell below 10-3 to 10-5 cm/d, depending on the soil. As drought progressed, oak and beech may also have benefited from their leaf osmoregulatory capacity, but at the cost of xylem embolism with around 50 % loss of hydraulic conductivity when soil water potential dropped below -1.25 MPa. Consideration of species-specific water use is crucial for forest management and vegetation modelling to improve forest resilience to drought.