Search

The Peters–Durner–Iden (PDI) model system for describing soil hydraulic properties (SHP) has been developed over a decade. Inspired by Rien van Genuchten's seminal work, the PDI system focuses on an efficient and simple parameterization of water retention curves and hydraulic conductivity curves (HCC) across the entire soil moisture spectrum. By combining capillary and non‐capillary components for water retention and conductivity, it aims to reconcile mathematical simplicity and insights on water adsorption and film flow in soils. Recent developments have reduced the number of free parameters of the conductivity model to zero, enhancing the model's applicability in cases of limited data availability. The first reduction was achieved by a prediction of absolute non‐capillary conductivity based on the consideration of film and corner flow on the pore scale, and the second by a prediction of absolute capillary conductivity by a capillary bundle model. This allows a complete characterization of SHP over the entire moisture range with only four retention curve parameters. The inclusion of a maximum pore size in the capillary conductivity model prevents an unrealistic drop of the HCC near saturation. This paper provides a comprehensive overview of the PDI model system, emphasizing its conceptual features and mathematical details. An Excel sheet and a Python code stored in a repository are provided for accessibility. Core Ideas: Compact and comprehensive mathematical overview of the current PDI system.The model integrates elements of capillary and non‐capillary soil water storage and conductivity in a simple manner.Hydraulic conductivity can be completely predicted from the retention curve.Improved applicability in cases where conductivity data are scarce or available only in a limited moisture range. [ABSTRACT FROM AUTHOR]

Recent models of the unsaturated hydraulic conductivity curve (UHCC) are the sum of separate UHCCs for domains of capillary water, film water, and water vapor. This requires parallel, noninteracting domains. A theoretical framework for aggregating domain conductivities to a bulk soil UHCC is presented to identify and possibly relax implicit assumptions about domain configuration. The paper develops arithmetic, harmonic, and geometric averages of the liquid‐water conductivities that can be arithmetically averaged with the vapor conductivity. However, current models for capillary and film conductivities are intrinsic, that is, valid within their respective domain. The vapor conductivity is a bulk conductivity, that is, it gives the conductivity of the gaseous domain as it manifests itself in the soil. Conversion relationships use the domain volume fractions as approximations of the as‐yet unknown weighting factors to convert between intrinsic and bulk conductivities. This facilitates consistent averaging of domain conductivities. Even with consistent averaging, a truly physically accurate model of the UHCC based on domain conductivities is fundamentally elusive. Nevertheless, models based on the three averages and the unweighted sum of the domain conductivities produce good fits to data for two soils but diverge in the dry range. The fitted curves for the capillary and film water depend on the averaging (or adding) method. Hence, they are not strictly characteristic of their respective domains. The true intrinsic domain conductivity functions may be impossible to determine. Core Ideas: Finding the soil hydraulic conductivity by summing capillary, film, and vapor conductivities has gained popularity.The capillary and film domains have intrinsic, not bulk domain conductivities. Conversion equations are developed.Summing domain bulk conductivities requires parallel domains. Harmonic and geometric averaging add flexibility.Conductivity curves based on arithmetic, harmonic, and geometric means fit the data but diverge in the dry range.A physically accurate soil hydraulic conductivity curve based on domain conductivities is fundamentally elusive. [ABSTRACT FROM AUTHOR]

Infiltration stormwater control measures (SCMs) have the potential to contribute towards mitigating the effects of urbanization on downstream receiving waters. Infiltration SCMs are most often successful when the in‐situ saturated hydraulic conductivity (Ksat) is well characterized. In this paper numerical solutions of the Richards' equation are used to quantify the bias of seven infiltration measurement methods, removing natural variability and random error from the analysis. The methods evaluated in this study include the double ring infiltrometer, Saturo infiltrometer, modified Philip–Dunne infiltrometer, Turf‐Tec IN2‐W infiltrometer, USBR 7300‐89 well permeameter, Philip–Dunne permeameter, and the Guelph permeameter. Seven homogenous, isotropic soil textures were simulated at four initial soil moistures for the seven methods, resulting in a total of 196 simulations. The dimensionless bias is defined as the "measured" Ksat determined by a given method divided by the Ksat input to the numerical experiments. The "measured" Ksat is in quotations to identify the measurement occurs in a numeric experiment rather than in a physical experiment. In sand through silt loam soils that are typical of infiltration SCMs, the simulated methods have a bias in the range of 0.7–6.2. The Turf‐Tec was the only infiltrometer that produced a bias >2.5 for these soils. Initial effective saturation had a minimal contribution to bias for most methods. Methods that rely on a one‐dimensional (1D) flow assumption consistently overestimated the Ksat. Borehole methods produced results with bias similar to surface methods. Long duration methods did not consistently produce more accurate results than short duration methods. Core Ideas: Small infiltration tests with 3D flow corrections can be fast and accurate, requiring less water.Infiltration measurement methods that use a 1D flow assumption consistently overestimate Ksat.Infiltration tests achieve reasonable accuracy in <1.1 h in coarse soils typical of infiltration stormwater control measures. [ABSTRACT FROM AUTHOR]

We examine the validity of the commonly used Hagen‐Poiseuille model of local resistance of porous media using direct numerical simulations. We provide theoretical arguments that highlight possible limitations of this model and formulate a new constitutive model that is based on the circularity of iso‐pressure surfaces. We compare the performance of both models on three different three‐dimensional artificial porous media. We show that the new model improves the root‐mean‐squared‐relative error from 59%, 48% and 32% for the HP model to 12%, 14% and 18% for the three porous media respectively. We anticipate that our approach may find broad application in network models of porous media that are typically build from 3D images with intricate pore geometries. Plain Language Summary: The flow of liquids through porous materials is an everyday problem with many applications ranging from groundwater flow, packed bed reactors, filter devices to blood flow through kidneys. The classical flow modeling approach has been to represent the porous medium as a lattice of circular tubes that represent the pore network and the hydraulic resistance in individual tubes is modeled assuming uniform flow with a parabolic velocity profile, called "Hagen‐Poiseuille" law. In this paper we show that this approach has limitations and provide a refined model for local hydraulic resistance based on the pore geometry of complex three‐dimensional porous media. In particular, we show that the circularity, a parameter that quantifies the "roundness" of a surface of equal pressure traversing a pore cross section, is key to predict the local hydraulic resistance. Key Points: We introduce a new definition for individual pores in heterogeneous porous media based on iso‐pressure surfacesWe employ direct numerical simulations to measure the local hydraulic conductivity and revisit the Hagen‐Poiseuille (HP) modelWe show that a circularity‐based model performs significantly better than the HP model, reducing the averaged error substantially [ABSTRACT FROM AUTHOR]

Accurate information about soil water retention curves (SWRCs) of sands is essential for evaluating groundwater recharge and vulnerability to contamination in many shallow sandy aquifers which are widespread on post glacial areas in Northern Europe and North America. Pedotransfer functions (PTFs) allow to estimate SWRC from basic physical characteristics of soils, such as textural composition. However, in the case of clean sands which are dominated by a single textural fraction, PTFs should be based on more detailed information given by the particle size distribution. In this study we evaluated three parametric PTFs, which estimate parameters of the van Genuchten SWRC based on empirical correlations to the parameters of soil particle size distribution, and five semi‐physical PTFs, which derive the pore size distribution from particle size distribution. PTFs were compared to SWRCs fitted to the results of drainage experiments on sandy soil samples from six locations in Gdańsk region (northern Poland). Although in all samples the content of silt and clay fractions was low (<3.5%), the differences in actual content of fines strongly influenced the shape of SWRC. In contrast, the amount of gravel fraction (varying from 1% to 35%) did not have significant effect on SWRC. Semi‐physical PTFs were found to be more accurate than parametric PTFs. The best overall performance was shown by the semi‐physical Chang and Cheng PTF. Among the parametric PTFs the best accuracy was obtained with the Schaap and Bouten method. However, all considered functions showed limited accuracy in higher suction range. Additionally, infiltration experiments were performed on four sites. SWRCs were obtained from ring infiltrometer tests using the Beerkan estimation of soil transfer parameters (BEST) method and from the tension infiltrometer (TI) tests using numerical solution of the inverse problem based on the Richards equation. In almost all cases the wetting SWRCs were characterized by higher values of the pressure scaling parameter α compared to SWRCs measured in drainage experiments, which is consistent with the well‐known phenomenon of hysteresis in soils. However, the BEST method resulted in significantly higher α and hydraulic conductivity Ks than TI, probably due to activation of the largest soil pores during ponded infiltration. Core Ideas: Semi‐physical pedotransfer functions were more accurate than parametric pedotransfer functions.Comparison of water retention curves from drainage and infiltration experiments showed significant hysteresis.Ring infiltrometer tests provided higher values of the van Genuchten parameter α and the saturated hydraulic conductivity than tension infiltrometer tests. [ABSTRACT FROM AUTHOR]

Digital samples offer many opportunities to study subsurface fluid flow and contaminant transport processes. The pore size distribution of especially fine‐textured porous media often covers many orders of magnitude in the length scale, which makes accurate microCT scanning and modeling of the underlying processes difficult. When a single‐resolution image is not capable of capturing all relevant details of a sample, one should scan the sample, or selected parts of it, at different resolutions. Combining multiple resolutions into one single sample for subsequent pore‐scale modeling is generally not possible due to limitations in computer memory and speed, thus making it necessary to create a simpler sample containing relevant information from the parent networks. We imaged four samples using different resolutions to capture the multiscale heterogeneity of a fine‐textured soil and combined them into one overall digital sample based on the original pore networks. The parent networks were characterized using their geometrical properties, correlations between these properties, and connectivity functions describing the network topologies. Our approach creates stochastic networks of arbitrary size with the same flow properties as the parent network. The method, implemented using the PoreStudio pore network model, repeatedly integrates information at two subsequent scales, with the resulting digital sample having the same hydraulic properties as the original samples. The procedure leads to more useful three‐dimensional digital models, facilitating basic analyses of underlying pore size distributions. Porosity calculations were compared with direct measurements, while those for the hydraulic conductivity were compared with estimates based on the particle size distribution and nearby field data. Core Ideas: A stochastic method was used to combine four computed microtomography samples with different resolutions into one digital sample.The approach was applied to a fine‐textured tropical soil with a very broad pore‐size distribution.The methodology kept the same digital porosity as the original pore networks and enhanced the flow properties. [ABSTRACT FROM AUTHOR]

Finding an explicit solution to the widely used Green–Ampt (G–A) one‐dimensional infiltration model has been subject of efforts for more than half a century. We derived an explicit semiempirical approach that combines accuracy with simplicity, a concept that has been generally neglected in previous studies. The equation is F=Kst(0.70635+0.324151+9.43456(S2Ks2t))$F\; = {K_s}\;t\;({0.70635 + 0.32415\sqrt {1 + 9.43456({\frac{{{S^2}}}{{{K_s}^2t}}})} })$, with F (L), Ks (L/T), S (L/T0.5) and t (T) being cumulative infiltration, saturated hydraulic conductivity, sorptivity, and time, respectively. Relative errors (ɛ) by the application of this equation generally do not exceed ±0.3% in most applied infiltration problems faced by water resources engineering today. We show both numerically and mathematically that │ɛ│> 0.3% could only occur if Kst/F > 0.904, a criterion that could apply to sand and loamy sand soils (i.e., coarse texture) and if they experience infiltration rates for over 6 h and 19 h, respectively. Hence, we also derived a simple linear adjustment in the model as Fadj ≅ 0.9796 F + 0.335 S2/Ks to address these longer infiltration rates, and to assure that ɛ remains within the expected ±0.3% range of uncertainty. A linearized regression technique was also developed to accurately estimate S and Ks when the G–A model is used. We numerically demonstrated that our fitting method could be used even when the G–A approach is less valid (diffusive soils), provided that the actual value of the capillary length (λ) is initially known. An added benefit of our approach is that by setting λ equal to 1/3 and 2/3, it can significantly limit the range of initializing, unknown, a priori values of S and Ks, as these two parameters are estimated through the inverse solution of implicit infiltration models. Due to the model's simplicity and accuracy, our solution should find application among hydrologists, natural resource scientists, and engineers who wish to easily derive accurate estimations from the G–A infiltration approach and/or estimate sorptivity and hydraulic conductivity without encountering divergence problems. Core Ideas: A new explicit form of the one‐dimensional Green–Ampt infiltration model was developed.This model combined simplicity, accuracy, and computational efficiency.A new linearized regression solution was derived to estimate sorptivity and hydraulic conductivity.This linearized fitting method can eliminate the risk of convergence associated with other numerical approaches. [ABSTRACT FROM AUTHOR]

Reliable estimates of saturated hydraulic conductivity (Ks) are usually difficult to obtain, as Ks is regulated by a variety of soil processes acting at different spatial scales that may obscure each other's impacts. We hypothesized that these scale‐specific relationships could be well characterized with the aid of the noise‐assisted multivariate empirical mode decomposition (NA‐MEMD), thereby serving as a solid foundation for an accurate Ks prediction. The objective was to evaluate whether the incorporation of NA‐MEMD could improve the estimation of Ks based on the multiscale associations it unraveled. On a typical slope transect of 860 m in the black soil region of northeast China, Ks, mollic epipedon thickness, bulk density, soil organic carbon content, total (ϕ) and effective porosities (ϕe), and particle size distribution were investigated at every 20 m. Prior to NA‐MEMD, Ks was most strongly correlated with ϕe, and the linear regression models based on ϕe solely were satisfactory for Ks estimation at the scale of investigation. Adding other predictors significantly improved Ks prediction in calibration, but impaired it in validation. Upon decomposition by NA‐MEMD, Ks was found to be significantly associated with each attribute at two scales of oscillation at least. Summing up the estimates of each Ks component derived from the properties at the equivalent oscillation scales, the results outperformed the traditional multiple linear regressions made at the investigation scale, when the same sets of predictors were used. The application of NA‐MEMD, moreover, could save the tedious measurements of ϕe and ϕ. Excluding these two porosity‐related properties, Ks estimates obtained by incorporating NA‐MEMD were statistically similar or even better than those involving them before NA‐MEMD. These findings demonstrate the great potential of NA‐MEMD in untangling scale‐dependent relationships of Ks with various processes and hold important implications for future estimations of Ks and other hydraulic properties in the black soil region of northeast China and similar regions. Core Ideas: Saturated hydraulic conductivity (Ks) was most strongly correlated with effective porosity (ϕe) in general both before and after decomposition with noise‐assisted multivariate empirical mode decomposition (NA‐MEMD).Linear regressions based on ϕe only were adequate for Ks prediction at the scale of investigation.Combining NA‐MEMD with multiple linear regression (MLR) predicted Ks more accurately than MLR performed at the measurement scale.Incorporating NA‐MEMD could save tedious measurements of total (ϕ) and effective (ϕe) porosities for Ks estimation. [ABSTRACT FROM AUTHOR]

Water retention and hydraulic conductivity characteristics are key input data in studies on soil water dynamics in the vadose zone. The most well‐known analytical functions to describe these characteristics are those given by Mualem and van Genuchten, where van Genuchten showed that both can be described by a limited set of shared parameters. Analytically, there are no restrictions on the range of pressure heads for which these characteristics can be used. Experience, however, has shown that for certain sets of parameters, the hydraulic conductivity cannot be computed accurately at low‐pressure heads. This is due to the accuracy of (double precision) floating point operations in computer code. It is shown that for low‐pressure heads, the Mualem function approaches a power function. An adapted version of the Mualem–van Genuchten (MvG) expression for the hydraulic conductivity is proposed: between saturation and a soil‐dependent critical pressure head, the classical Mualem expression is valid and below this critical pressure head a power function is used. The power function is defined such that it matches the Mualem value at the critical pressure head. No accuracy problems will occur when using the power function until the result approaches the smallest possible (double precision) floating point value that significantly differs from zero. Core Ideas: Computer calculated hydraulic conductivities K can show anomalous behavior at low‐pressure heads h.Double precision floating point constraints are the main cause.The Mualem–van Genuchten K expression can be approximated by a power function at low h.An extended expression for the Mualem–van Genuchten K(h) equation is proposed.With the extended expression, K can be computed to values as low as floating point precision allows. [ABSTRACT FROM AUTHOR]

Keywords: hydraulic conductivity; rhizosphere; root-soil contact; soil drying; stomata; transpiration EN hydraulic conductivity rhizosphere root-soil contact soil drying stomata transpiration 1541 1543 3 05/20/20 20200615 NES 200615 The recent paper by Rodriguez-Dominguez & Brodribb ([9]) shows that the loss in soil-root hydraulic conductance is the primary constraint on water flow during water stress (soil water potential below -1 MPa) and that this initiates stomata closure. This is an important result as it highlights the link between stomatal regulation and belowground soil-root interactions, particularly those taking place at the root-soil interface and in the adjacent soil, the I rhizosphere i . Remarkably, as the soil dried out, root and soil-root interface hydraulic conductances dropped significantly and became the primary constraint on water flow, more than xylem cavitation. Despite stomatal closure alleviating the loss of soil hydraulic conductance I K i SB soil sb , soil drying caused a large drop of hydraulic conductance at the root-soil interface I K SB i sb i . [Extracted from the article]

Degraded peatlands release large amounts of greenhouse gases. The development of effective mitigation and management measures requires an understanding of relevant site‐specific biogeochemical and hydraulic processes. However, the simulation of water fluxes and vadose zone state variables of degrading peatlands relies on proper process description, parameterization of hydraulic functions, and representation of the boundary conditions. The objective of this study was to analyze the effects of unimodal versus bimodal soil hydraulic functions and pressure head versus flux‐type lower boundary conditions (LBCs) on the calculated hydraulic characteristics of a degraded peat profile. HYDRUS‐1D was used to study the hydraulic flow dynamics parameterized with data from a weighable groundwater lysimeter for the period from May 1 to December 31, 2019. Simulations comparing uni‐ and bimodal hydraulic functions showed only minor differences. Simulations of soil water pressure at a depth of 30 cm using a flux‐type LBC (RMSE: 27 cm, where RMSE is root mean square error) performed better than simulations using a pressure head LBC (RMSE: 48 cm). The pressure head LBC performed better at simulating volumetric water contents in 30‐cm depth than the flux LBC variant (RMSE: 0.05 vs. 0.09 cm3 cm−3). For specific site conditions with a shallow, fluctuating groundwater table and temporary air entrapment, the choice of LBC was important for a more accurate simulation of soil water fluxes and volumetric water content. Core Ideas: Understanding degraded peatland hydraulics based on groundwater lysimeter data.Simulation of the peat soil water balance as affected by water table dynamics.Comparing unimodal with bimodal soil hydraulic models in water balance simulation.Analyzing the choice of the lower boundary conditions by scenario simulations.Discussion on missing processes not accounted for to improve simulation results. [ABSTRACT FROM AUTHOR]

Numerical modeling of soil water dynamics and storage is generally based on the Richards equation. Its solution requires knowledge of the soil hydraulic properties (SHP): the soil water retention function and the hydraulic conductivity function. To determine SHP, laboratory evaporation experiments are particularly popular because they provide data for both SHP functions. The evaluation by the simplified evaporation method (SEM) method, originally proposed by Schindler and subsequently improved by several authors, relies on linearization assumptions that allow for a relatively simple calculation scheme but result in biased conductivity data for some soils. The objective of this study is to propose and test an improved computational scheme for the hydraulic conductivity function. We present the new theory and show that it leads generally to higher accuracy of the conductivity function. The improvement is most pronounced for sandy soils and soil water pressure heads below −100 cm, where the original method provided data with bias. Core Ideas: An improved scheme for the calculation of hydraulic conductivity with the simplified evaporation method (SEM) is presented.Bias in hydraulic conductivity for sandy soils was observed in the original SEM is eliminated.Improvement is most significant for soil water pressure heads in the medium to dry range, below −100 cm.The calculation scheme can be easily implemented in existing computer algorithms. [ABSTRACT FROM AUTHOR]

Local waterlogging often occurs on the steep slopes of clayey–calcareous soils in southwestern France, causing nutrients and pollutants transfer to the river bodies and reduced ecosystems services. These soils developed in the Miocene molassic hill formation and are generally impermeable with abundant traces of hydromorphy and heterogenous spatial distribution. This article aims to describe the hydrological functioning of these soils, based on a cross analysis of pedological, hydrological, and geophysical characterizations. Our experimental site is the catchment area located in Auradé (southwestern France). Here, we analyze the flows at the outlet of the studied watershed together with piezometric and climatic monitoring from September 2020 to September 2021. We show that the hydrological year is divided into three phases: first, a soil recharge phase with an effective rainfall of about 100 mm; second, a saturation phase, when 80% of the effective precipitation is drained mostly by runoff and hypodermic flows; third, a drying phase. Soil waterlogging events usually occur during the saturation phase. They are due to several forms of flow: surface runoff associated with return flow, hypodermic flow caused by the presence of soil layers with lower hydraulic conductivity in the subsurface (swelling clays and plowing sole) and groundwater flow with intermittent connection of the soil water table in the hillside to the alluvial groundwater table. We also conducted independent seismic refraction tomography analyses that validate localized waterlogging patterns along the catchment and open the way to spatializing areas with high waterlogging potential at the scale of the study plot. Core Ideas: An interdisciplinary approach (pedology, hydrology, and geophysics) highlights flow paths in hilly calcisols.Seismic geophysics reveals heterogeneities of the molasse material that drives intermittent downslope connectivity.Soil porosity value around 100 mm both corresponds to the soils water adsorption and water supply capacities.The sand lens acts like a local captive aquifer for a period of 4 months starting in winter. [ABSTRACT FROM AUTHOR]

With ongoing climate change and the increase in extreme weather events, especially droughts, the challenge of maintaining food security is becoming ever greater. Locally adapted landraces of crops represent a valuable source of adaptation to stressful environments. In the light of future droughts—both by altered soil water supply and increasing atmospheric water demand (vapor pressure deficit [VPD])—plants need to improve their water efficiency. To do so, plants can enhance their access to soil water by improving rhizosphere hydraulic conductivity via the exudation of mucilage. Furthermore, plants can reduce transpirational water loss via stomatal regulation. Although the role of mucilage and stomata regulation on plant water management have been extensively studied, little is known about a possible coordination between root mucilage properties and stomatal sensitivity as well as abiotic drivers shaping the development of drought resistant trait suits within landraces. Mucilage properties and stomatal sensitivity of eight Mexican landraces of Zea mays in contrast with one inbred line were first quantified under controlled conditions and second related to water demand and supply at their respective site of origin. Mucilage physical properties—namely, viscosity, contact angle, and surface tension—differed between the investigated maize varieties. We found strong influences of precipitation seasonality, thus plant water availability, on mucilage production (R2 =.88, p <.01) and mucilage viscosity (R2 =.93, p <.01). Further, stomatal sensitivity to increased atmospheric water demand was related to mucilage viscosity and contact angle, both of which are crucial in determining mucilage's water repellent, thus maladaptive, behavior upon soil drying. The identification of landraces with pre‐adapted suitable trait sets with regard to drought resistance is of utmost importance, for example, trait combinations such as exhibited in one of the here investigated landraces. Our results suggest a strong environmental selective force of seasonality in plant water availability on mucilage properties as well as regulatory stomatal effects to avoid mucilage's maladaptive potential upon drying and likely delay critical levels of hydraulic dysfunction. By this, landraces from highly seasonal climates may exhibit beneficial mucilage and stomatal traits to prolong plant functioning under edaphic drought. These findings may help breeders to efficiently screen for local landraces with pre‐adaptations to drought to ultimately increase crop yield resistance under future climatic variability. [ABSTRACT FROM AUTHOR]

The KINEROS2 model was utilized for runoff simulation in the Dehgin catchment situated in the Hormozgan province of Iran. A parameter allocation procedure was used in lieu of parameter optimization. After parameter allocation, the model was able to adequately simulate hydrographs associated with high‐magnitude peak discharge events with the efficiency values between 0.011–0.83 for Nash–Sutcliffe and 0.36–0.98 for Kling–Gupta, but the model did not accurately simulate hydrographs corresponding to low‐magnitude peak discharge events. Although calibration after parameter allocation improved model performance with respect to the simulation of low‐magnitude discharge events, numerical values of the hydraulic conductivity and net capillary pressure as the most sensitive model parameters did not agree with parameters known to be reasonable in the region. So that the value of hydraulic conductivity was decreased from 61 to 55 mm/h in channels and from 3.7 to 1.7 mm/h in planes. The new values are physically reasonable but are not approximately the same as physical values associated with the regional and environmental context of the Dehgin catchment. In this case, the values of the evaluation criteria were obtained between −2.5 and 0.78 for Nash–Sutcliffe and 0.17 and 0.98 for Kling–Gupta. The results of using the HydroPSO package in R to automated calibration of the model, with the value of Nash–Sutcliffe between −0.63 and 0.43, indicated that autocalibration without intelligent and deliberate selection of parameters cannot accurately represent hydrological processes, and therefore should be avoided. Also, the results show that an understanding of the catchment environmental conditions and appropriate allocation of parameters is initially more effective as a first step of the modeling process and thereby contributes to a first‐order characterization of environmental conditions in the catchment. Recommendations for Resource Managers: A better understanding of the catchment and model behavior helps the resource managers to have a better simulation of the hydrologic system and to achieve a better water resources management of the study area.Although parameter calibration is often unavoidable while working with some models, it should be minimized, and only conducted after parameter allocation. Some minimal calibration or adjustments after parameter allocation may lead to a better simulation of the hydrologic system, which will be beneficial for management purposes. [ABSTRACT FROM AUTHOR]

Summary: Although xylem embolism is a key process during drought‐induced tree mortality, its relationship to wood anatomy remains debated. While the functional link between bordered pits and embolism resistance is known, there is no direct, mechanistic explanation for the traditional assumption that wider vessels are more vulnerable than narrow ones.We used data from 20 temperate broad‐leaved tree species to study the inter‐ and intraspecific relationship of water potential at 50% loss of conductivity (P50) with hydraulically weighted vessel diameter (Dh) and tested its link to pit membrane thickness (TPM) and specific conductivity (Ks) on species level.Embolism‐resistant species had thick pit membranes and narrow vessels. While Dh was weakly associated with TPM, the P50–Dh relationship remained highly significant after accounting for TPM. The interspecific pattern between P50 and Dh was mirrored by a link between P50 and Ks, but there was no evidence for an intraspecific relationship.Our results provide robust evidence for an interspecific P50–Dh relationship across our species. As a potential cause for the inconsistencies in published P50–Dh relationships, our analysis suggests differences in the range of trait values covered, and the level of data aggregation (species, tree or sample level) studied. [ABSTRACT FROM AUTHOR]

Water table elevation is a key feature for identifying the groundwater behaviour. Accordingly, appropriate measurements—in terms of both frequency and spatial distribution—play a crucial role for capturing the aquifer response to recharge and withdrawals. However, numerical models simulating the main features of the behaviour of the water table elevation may help groundwater management, as an additional tool. In this article, soil moisture data from three well‐established global reanalyses (ERA5, CFS, and JRA‐55) are used for evaluating the flux in the vadose zone towards shallow unconfined aquifers, Fg$$ {F}_g $$, in the Umbria region (central Italy). Then, according to the methodology proposed in Bongioannini Cerlini et al. (2021), where for the considered aquifers most of the recharge derives from the unsaturated zone, Fg$$ {F}_g $$ is used for simulating the water table evolution in time. With the aim of assessing which reanalysis is the most appropriate in simulating the evolution of groundwater levels, the properties of the correspondent land surface models (LSM) are examined, as they provide Fg$$ {F}_g $$. For the considered aquifers, the analysis of the performance of the selected reanalyses confirms the validity of the proposed approach. Moreover, it points out the crucial role of the spreading of the water table elevation with respect to its mean value, as a significant parameter for selecting the most adequate reanalysis to use. In addition, the role in the LSM of the explored soil depth, hydraulic conductivity curve, and spatial resolution is highlighted. These results, in line with recent literature on the performance of the reanalyses, suggest to extend future work to other regions of the world. [ABSTRACT FROM AUTHOR]

Hydraulic nonequilibrium in soil during water infiltration and drainage is a well‐known phenomenon. During infiltration, water initially invades easily accessible pores before it slowly redistributes towards some state of energetic minimum. In analogy, during drainage, easily drainable pores are emptied more rapidly than those blocked by bottlenecks. The consequence is that the water content is lagging behind the water potential and both state variables do not follow a unique water retention curve as typically assumed when applying Richards equation. Current models that account for nonequilibrium allow for the required decoupling of water content and water potential; however, they do not consider the consequences for the hydraulic conductivity. In this contribution, we present a physically based approach to estimate hydraulic conductivity during nonequilibrium, which depends on both water content and water potential during nonequilibrium conditions. This approach of a dynamic hydraulic conductivity function is demonstrated for an infiltration process into relatively dry soil and for a stepwise drainage and rewetting with decreasing and increasing water fluxes (i.e., multistep flux experiment). The new approach reproduces well‐known phenomena such as pressure overshoot and preferential flow across infiltration fronts using a unified concept for hydraulic conductivity. This was not possible with existing models assuming some fixed unsaturated conductivity function depending on either water content or water potential. Core Ideas: Soils are rarely in hydraulic equilibrium.We show consequences for their effective hydraulic conductivity.We present a physically based concept how to better describe the unsaturated conductivity function.The new approach describes pressure overshoot across fronts and the emergence of preferential during infiltration. [ABSTRACT FROM AUTHOR]

Summary: Disruption of photosynthesis and carbon transport due to damage to the tree crown and stem cambial cells, respectively, can cause tree mortality. It has recently been proposed that fire‐induced dysfunction of xylem plays an important role in tree mortality. Here, we simultaneously tested the impact of a lethal fire dose on nonstructural carbohydrates (NSCs) and xylem hydraulics in Pinus ponderosa saplings.Saplings were burned with a known lethal fire dose. Nonstructural carbohydrates were assessed in needles, main stems, roots and whole plants, and xylem hydraulic conductivity was measured in the main stems up to 29 d postfire.Photosynthesis and whole plant NSCs declined postfire. Additionally, all burned saplings showed 100% phloem/cambium necrosis, and roots of burned saplings had reduced NSCs compared to unburned and defoliated saplings. We further show that, contrary to patterns observed with NSCs, water transport was unchanged by fire and there was no evidence of xylem deformation in saplings that experienced a lethal dose of heat from fire.We conclude that phloem and cambium mortality, and not hydraulic failure, were probably the causes of death in these saplings. These findings advance our understanding of the physiological response to fire‐induced injuries in conifer trees. [ABSTRACT FROM AUTHOR]

Premise: Rhizomatous growth characterizes numerous taxa among vascular plants. While abundant information exists on nutrient sharing and demography, the question of how these metameric organisms move water through their bodies remains largely unstudied. Moreover, we lack an understanding of the evolutionary implications of rhizomatous growth across vascular plants. Here, we examined these questions by investigating how rhizomatous growth and vascular construction affect whole‐plant hydraulic function. Methods: In five terrestrial fern species with diverse vascular construction, we used microcomputed tomography and bright‐field microscopy to examine vascular construction across nodes along the rhizome. These data were integrated with measurements of leaf stomatal conductance under rooted and uprooted conditions to relate vascular patterning and hydraulic architecture to leaf water status. Results: Similar to phytomers of woody seed plants, nodal regions in rhizomatous ferns are areas of hydraulic resistance. While water is shared along the rhizomes of these investigated species, hydraulic conductivity drops at nodes and stomatal conductance declines when nodes were locally uprooted. Together, our data suggest that nodes are chokepoints in axial water movement along the rhizome. Conclusions: Nodal chokepoints decrease hydraulic integration between phytomers. At the same time, chokepoints may act as "safety valves", hydraulically localizing each phytomer—potentially decreasing embolism and pathogen spread. This suggests a potential trade‐off in the principal construction of the fern rhizome. Moreover, we propose that shoot‐borne roots (homorhizy) and the prostrate habit of rhizomatous ferns decrease the hydraulic and structural burdens that upright plants typically incur. The absence of these hydraulic and structural demands may be one reason ferns (and many rhizomatous plants) lack, or have minimally developed, secondary xylem. [ABSTRACT FROM AUTHOR]

1. Tree survival affects forest biodiversity, structure and functioning. However, little is known about feedback effects of biodiversity on survival and its dependence on functional traits and interannual climatic variability. 2. With an individual-based dataset from a large subtropical forest biodiversity experiment, we evaluated how species richness, functional traits and time-dependent covariates affected annual tree survival rates from age 3–12 (years) after planting 39 species across a diversity gradient from 1 to 2, 4, 8 and 16 tree species. 3. We found that overall survival rates marginally increased with diversity at the plot level, with large variation among plots within diversity levels. Significant variation among species in survival responses to diversity and changes in these responses with age were related to species functional traits and climatic conditions. Generally, survival rates of conservative species (evergreen, late-successional species with thick leaves and high carbon to nitrogen ratio but low specific leaf area, leaf phosphorus and hydraulic conductivity) increased with diversity, age and yearly precipitation, whereas acquisitive species showed opposite responses. 4. Synthesis. Our results indicate that interactions between diversity, species functional traits and yearly climatic conditions can balance survival among species in diverse forests. Planting mixtures of species that differ in functional traits in afforestation projects may lead to a positive feedback loop where biodiversity maintains biodiversity, together with its previously reported beneficial effects on ecosystem functioning. [ABSTRACT FROM AUTHOR]

Summary: Xylem embolism impairs hydraulic conductivity in trees and drives drought‐induced mortality. While embolism has been monitored in vivo in potted plants, and research has revealed evidence of embolism in field‐grown trees, continuous in situ monitoring of cavitation in forests is lacking.Seasonal patterns of embolism were monitored in branchlets of Aleppo pine (Pinus halepensis) trees growing in a dry Mediterranean forest. Optical visualization (OV) sensors were installed on terminal branches, in addition to monthly sampling for micro computed tomography scans.We detected 208 cavitation events among four trees, which represented an embolism increase from zero to c. 12% along the dry season. Virtually all the cavitation events occurred during daytime hours, with 77% occurring between 10:00 and 17:00 h. The probability for cavitation in a given hour increased as vapor pressure deficit (VPD) increased, up to a probability of 42% for cavitation when VPD > 5 kPa.The findings uniquely reveal the instantaneous environmental conditions that lead to cavitation. The increased likelihood of cavitation events under high VPD in water‐stressed pines is the first empirical support for this long hypothesized relationship. Our observations suggest that low levels of embolism are common in Aleppo pine trees at the dry edge of their distribution. [ABSTRACT FROM AUTHOR]

Alluvial sand and gravel (ASG) aquifers are highly heterogeneous and exhibit strong, spatially variable anisotropy, often interspersed by buried paleo‐channels of increased hydraulic conductivity. Groundwater flow and solute transport is often characterized by preferential flow caused by anisotropic properties in ASG aquifers. Connected ASG subsurface structures such as buried paleo‐channels, however, are difficult to reproduce with commonly used techniques, and anisotropy is rarely considered in applied groundwater models. To ease the notoriously difficult problem of how to consider anisotropy, we propose a novel modeling framework based on calibration of an integrated surface‐subsurface hydrological model via spatially varying, preferred anisotropy pilot point inversion. The inversion leverages hydraulic and tracer‐based observations representing multiple spatial and temporal scales. We demonstrate the applicability of the framework on a real‐world ASG site used for drinking water production, and we quantify the information content of observations to identify connected paleo‐channels and provide guidance for optimal field‐data acquisition. Plain Language Summary: Mountainous river corridors are used worldwide for drinking water production, as they represent a relatively safe and sustainable source of drinking water. The valley‐fill of mountainous river corridors is a result of millennia of fluvio‐glacial erosion and deposition via braided river systems and consists primarily of poorly sorted sand and gravel. Groundwater flow and solute transport through such alluvial sand and gravel (ASG) aquifers is characterized by preferential flow paths caused by formerly active, now buried meanders (i.e., paleo‐channels). The identification of paleo‐channels in ASG aquifers is crucial for safe drinking water production, but they are notoriously difficult to identify with the commonly used techniques. We propose a new modeling framework based on the calibration of an integrated surface‐subsurface hydrological model via spatially varying, preferred anisotropy pilot point inversion using both hydraulic and tracer observations. The new modeling framework is more efficient than other approaches to model flow through complex ASG aquifers and doesn't require precise prior knowledge of the location of paleo‐channels. The applicability and robustness of the framework is demonstrated on an ASG drinking water wellfield located in the Swiss Alps. Key Points: Novel framework for identifying and quantifying groundwater flow through buried paleo‐channelsHeterogeneous hydraulic conductivity fields were identified based on spatially varying, preferred anisotropy‐constrained inversionThe fraction of infiltrating stream water in the aquifer and stream‐aquifer exchange fluxes best inform the paleo‐channel [ABSTRACT FROM AUTHOR]

Summary: Predicting species‐level responses to drought at the landscape scale is critical to reducing uncertainty in future terrestrial carbon and water cycle projections.We embedded a stomatal optimisation model in the Community Atmosphere Biosphere Land Exchange (CABLE) land surface model and parameterised the model for 15 canopy dominant eucalypt tree species across South‐Eastern Australia (mean annual precipitation range: 344–1424 mm yr−1). We conducted three experiments: applying CABLE to the 2017–2019 drought; a 20% drier drought; and a 20% drier drought with a doubling of atmospheric carbon dioxide (CO2).The severity of the drought was highlighted as for at least 25% of their distribution ranges, 60% of species experienced leaf water potentials beyond the water potential at which 50% of hydraulic conductivity is lost due to embolism. We identified areas of severe hydraulic stress within‐species' ranges, but we also pinpointed resilience in species found in predominantly semiarid areas. The importance of the role of CO2 in ameliorating drought stress was consistent across species.Our results represent an important advance in our capacity to forecast the resilience of individual tree species, providing an evidence base for decision‐making around the resilience of restoration plantings or net‐zero emission strategies. [ABSTRACT FROM AUTHOR]

Hydraulic fracturing has become a standard stimulation technology to enhance hydrocarbon production in unconventional reservoirs in recent decades. During organic‐rich tight carbonate reservoir stimulation, extensive microfractures will be created and pre‐existing microfractures will be opened in the far‐field during hydraulic fracturing, but they tend to close after the release of hydraulic pressure due to the larger sizes of the conventional proppants not fitting into the microfractures. The well productivity will be further enhanced if these microfractures can be held open during production, like the primary hydraulic fractures supported by proppants. Based on this idea, industry has introduced microproppants into the pad or pre‐pad fluid so that they can be placed into opened microfractures during hydraulic fracturing. In this work, we propose further enhancing the stimulation efficiency by introducing solid delayed acid generating materials (SDAGM)‐coated microproppants into the stimulation for the dual function of keeping microfractures open, and, through subsequent reactions of the coating materials with the carbonate formation, creating extra void space inside the microfractures. To prove this concept and help select the appropriate microproppant coating plan, lattice Boltzmann simulation is performed to measure the hydraulic conductivity of the stimulated microfractures under different scenarios that represent corresponding stimulation treatment schemes. The simulations showed that fracture conductivity of the microfractures can be significantly improved by placing SDAGM‐coated microproppant into them. Using the mixed uncoated and SDAGM‐coated microproppants (Scheme II) may have better fracture conductivity improvement than using the coated microproppant alone (Scheme I). [ABSTRACT FROM AUTHOR]

We studied a pristine, prominently patterned raised bog in Tierra del Fuego, Argentina, to disentangle the complex interactions among plants and water and peat. The studied bog lacks complicating features often posed by other bogs. It is completely dominated by Sphagnum magellanicum, which covers all niches and growth forms, and is joined by only a dozen higher plant species; it is entirely ombrotrophic with very sharp borders to the surrounding fen; it has only one type of peat that shows an only limited range in degree of decomposition; and it is situated in a very even climate with minimal differences in rainfall and temperature over the year. We present detailed measurements along a 498‐m‐long transect crossing the bog, including water table measurements (n = 498), contiguous vegetation relevés (n = 248), hydraulic conductivity just below the water table (n = 246), and hydraulic conductivity in 11 depth profiles (n = 291); degree of humification of the corresponding peat was assessed in conjunction with the hydraulic conductivity measurements (n = 537). Sphagnum magellanicum moss samples were collected every 2 m along this transect as well and genotyped (n = 242). In addition, along short, 26‐m‐long transects crossing strings and flarks water table and hydraulic conductivity just below the water table were measured every meter. Sphagnum growth forms were assessed, and the vegetation of the entire bog was mapped in 10 × 10‐m relevés (n = 3322). A simulation model was applied to a generalized shape of the bog and produced surface patterns that well matched those seen in the field. The results were integrated with information from the literature and discussed in the framework of a self‐regulating and self‐organizing raised bog. We identified 19 hydrological feedback mechanisms. We found that the various mechanisms overlap in both space and time, which means there is redundancy in the self‐regulation of the system. Raised bogs, when in a natural state, are among the most resilient ecosystems known; resilience that is provided by feedbacks and backup systems to these feedbacks. [ABSTRACT FROM AUTHOR]

In humid temperate forests, the occurrence of frequent freeze–thaw cycles (FTC) is a main factor limiting tree growth, as xylem embolism induced by FTC poses a serious threat to the hydraulic integrity of trees. A high resilience to hydraulic dysfunction involves the enhancement of embolism resistance and/or extra non‐structural carbohydrate (NSC) inputs for restoration of an impaired hydraulic system. However, potentially negative implications of such NSC allocation on tree growth have not yet been explored.At a temperate forest site of northeast China, we studied xylem hydraulics and NSC contents in relation to winter embolism resilience in 15 sympatric broadleaf tree species belonging to three genera with relatively high species richness, but having distinct strategies in maintaining hydraulic integrity over the winter, that is, Acer species that generate positive stem and root pressures contributing to winter embolism refilling, Betula species that only generate root pressure and Populus species that do not generate positive pressure.Acer and Betula species had higher soluble sugar contents in the dormant season and indeed had higher hydraulic resilience to FTC‐induced embolism but slower stem growth. Populus species had higher NSC contents during the growing season and their faster stem growth was also consistent with higher hydraulic efficiency and leaf photosynthetic rate. The positive correlation between tree trunk radial growth rate and hydraulic conductivity suggests that xylem water transport efficiency can be a fundamental basis for tree productivity due to a significant hydraulic‐photosynthetic coordination. The negative correlation between soluble sugar concentration in the dormant season and stem growth rate indicates that metabolic carbon costs for enhancing hydraulic resilience may compromise tree growth during the growing season.Comparisons among Acer, Betula and Populus and the correlation analyses based on phylogenetic independent contrasts strongly support the existence of a trade‐off between hydraulic resilience against FTC‐induced embolism and growth rate among sympatric tree species under humid temperate climate conditions. This trade‐off has likely contributed to the sorting of temperate tree species and genera to different niches along environmental gradients with respect to freezing stress and interspecific competition. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Xylem hydraulic safety and efficiency are key traits determining tree fitness in a warmer and drier world. While numerous plant hydraulic studies have focused on branches, our understanding of root hydraulic functioning remains limited, although roots control water uptake, influence stomatal regulation and have commonly been considered as the most vulnerable organ along the hydraulic pathway.We investigated 11 traits related to xylem safety and efficiency along the hydraulic pathway in four temperate broad‐leaved tree species.Continuous vessel tapering from coarse roots to stems and branches caused considerable reduction in hydraulic efficiency. Wood density was always lowest in roots, but did not decline linearly along the flow path. In contrast, xylem embolism resistance (P50) did not differ significantly between roots and branches, except for one species. The limited variation in xylem safety between organs did not adequately reflect the corresponding reductions in vessel diameter (by ~70%) and hydraulic efficiency (by ~85%). Although we did not observe any trade‐off between xylem safety and specific conductivity, vessel diameter, vessel lumen fraction and wood density were related to embolism resistance, both across and partly within organs.We conclude that coarse roots are not highly vulnerable to xylem embolism as commonly believed, indicating that hydraulic failure during soil drying might be restricted to fine roots. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Closed‐form expressions of the hydraulic conductivity function for linearly superposed subretention (multimodal) functions were derived for arbitrary sets of the Brooks and Corey (BC), van Genuchten (VG), and Kosugi (KO) water retention models. The generalized Mualem hydraulic conductivity model was evaluated using the mathematical approach of Priesack and Durner. Three types of modification to the multimodel were also proposed. Firstly, the derived conductivity equations can be simplified when the submodel parameters, hbi${h_{{{\rm{b}}_i}}}$ for the BC model, αi−1${{\alpha}}_i^{ - 1}$ for the VG model, and hmi${h_{{{\rm{m}}_i}}}$ for the KO model have the same (common) value (denoted as CH). Secondly, as in the case of the modified single VG and KO models, a hypothetical air‐entry head near saturation can be introduced for the multimodal VG and KO models to prevent unrealistic reductions in the hydraulic conductivity near saturation when the VG n parameter approaches its lower limit of n = 1. Furthermore, the multimodal hydraulic conductivity functions become a simple sum of conductivity subfunctions when the exponent r is unity (such as for Burdine's model), which leads to independent tortuosity effects for each submodel. The models are illustrated for two soils: a highly aggregated Kumamoto Andisol and a relatively unimodal dune sand. The dual‐(BC, VG, KO) and the VG1BC2 models equally represented the water retention data of the Andisol, with similar hydraulic conductivity curves. The dual‐BC‐CH, dual‐VG‐CH, and VG1BC2‐CH models fitted the water retention data of the dune sand well, with the hydraulic conductivity curves of the dual‐porosity model being similar to those of the Fayer and Simmons (FS) model. Core Ideas: Mualem‐based hydraulic conductivity functions for multimodal retention models are derived.The approach uses the Brooks–Corey, van Genuchten, and Kosugi water retention models.The multimodal equations describe the hydraulic properties from saturated to dry conditions.The closed‐form equations are attractive for flow simulations because of their simple form. [ABSTRACT FROM AUTHOR]

Summary: The formation of Casparian strips (CS) and the deposition of suberin at the endodermis of plant roots are thought to limit the apoplastic transport of water and ions. We investigated the specific role of each of these apoplastic barriers in the control of hydro‐mineral transport by roots and the consequences on shoot growth.A collection of Arabidopsis thaliana mutants defective in suberin deposition and/or CS development was characterized under standard conditions using a hydroponic system and the Phenopsis platform.Mutants altered in suberin deposition had enhanced root hydraulic conductivity, indicating a restrictive role for this compound in water transport. In contrast, defective CS directly increased solute leakage and indirectly reduced root hydraulic conductivity. Defective CS also led to a reduction in rosette growth, which was partly dependent on the hydro‐mineral status of the plant. Ectopic suberin was shown to partially compensate for defective CS phenotypes.Altogether, our work shows that the functionality of the root apoplastic diffusion barriers greatly influences the plant physiology, and that their integrity is tightly surveyed. [ABSTRACT FROM AUTHOR]

Premise: Among the sophisticated trap types in carnivorous plants, the underground eel traps of corkskrew plants (Genlisea spp., Lentibulariaceae) are probably the least understood in terms of their functional principle. Here, we provide a detailed analysis of structural and hydraulic features of G. hispidula traps, contributing to the ongoing debate on whether these traps can actively generate water streams to promote prey capture. Methods: Anatomical and hydraulic traits of detached traps, including inner trap diameters, chamber line element, hair length, glandular pattern, and hydraulic conductivity, were investigated quantitatively using light and electron microscopy, x‐ray microtomography, and hydraulic measurements. Results: Hydraulic resistivity in the neck of the trap, from the trap mouth toward the vesicle (digestive chamber) was 10 times lower than in the opposite direction. The comparison of measured and theoretical flow rates suggests that the retrorse hairs inside trap necks also provide considerable resistance against movement of matter toward the vesicle. Hairs showed a gradient in length along the neck, with the shortest hairs near the vesicle. Co‐occurrence of quadrifid and bifid glands was limited to a small part of the neck, with quadrifids near the vesicle and bifids toward the trap mouth. Conclusions: The combination of structural gradients with hydraulic anisotropy suggests the trap is a highly fine‐tuned system based on likely trade‐offs between efficient prey movement in the trap interior toward the vesicle, prey retention, and spatial digestion capacities and is not counter to the generation of water streams. [ABSTRACT FROM AUTHOR]

Summary: Deep‐water access is arguably the most effective, but under‐studied, mechanism that plants employ to survive during drought. Vulnerability to embolism and hydraulic safety margins can predict mortality risk at given levels of dehydration, but deep‐water access may delay plant dehydration. Here, we tested the role of deep‐water access in enabling survival within a diverse tropical forest community in Panama using a novel data‐model approach.We inversely estimated the effective rooting depth (ERD, as the average depth of water extraction), for 29 canopy species by linking diameter growth dynamics (1990–2015) to vapor pressure deficit, water potentials in the whole‐soil column, and leaf hydraulic vulnerability curves. We validated ERD estimates against existing isotopic data of potential water‐access depths.Across species, deeper ERD was associated with higher maximum stem hydraulic conductivity, greater vulnerability to xylem embolism, narrower safety margins, and lower mortality rates during extreme droughts over 35 years (1981–2015) among evergreen species. Species exposure to water stress declined with deeper ERD indicating that trees compensate for water stress‐related mortality risk through deep‐water access.The role of deep‐water access in mitigating mortality of hydraulically‐vulnerable trees has important implications for our predictive understanding of forest dynamics under current and future climates. [ABSTRACT FROM AUTHOR]

Summary: Plant hydraulic traits are key for understanding and predicting tree drought responses. Information about the degree of the traits' intra‐specific variability may guide the selection of drought‐resistant genotypes and is crucial for trait‐based modelling approaches.For the three temperate minor broadleaf tree species Acerplatanoides, Carpinus betulus and Tilia cordata, we measured xylem embolism resistance (P50), leaf turgor loss point (PTLP), specific hydraulic conductivity (KS), Huber values (HVs), and hydraulic safety margins in adult trees across a precipitation gradient. We further quantified trait variability on different organizational levels (inter‐specific to within‐canopy variation), and analysed its relationship to climatic and soil water availability.Although we observed a certain intra‐specific trait variability (ITV) in safety‐related traits (P50, PTLP) with higher within‐tree and between‐tree than between populations variability, the magnitude was small compared to inter‐specific differences, which explained 78.4% and 58.3% of the variance in P50 and PTLP, respectively. In contrast, efficiency‐related traits (KS, HV) showed a high ITV both within populations and within the crowns of single trees. Surprisingly, the observed ITV of all traits was neither driven by climatic nor soil water availability.In conclusion, the high degree of conservatism in safety‐related traits highlights their potential for trait‐based modelling approaches. [ABSTRACT FROM AUTHOR]

Summary: Wood anatomical traits shape a xylem segment's hydraulic efficiency and resistance to embolism spread due to declining water potential. It has been known for decades that variations in conduit connectivity play a role in altering xylem hydraulics. However, evaluating the precise effect of conduit connectivity has been elusive. The objective here is to establish an analytical linkage between conduit connectivity and grouping and tissue‐scale hydraulics.It is hypothesized that an increase in conduit connectivity brings improved resistance to embolism spread due to increased hydraulic pathway redundancy. However, an increase in conduit connectivity could also reduce resistance due to increased speed of embolism spread with respect to pressure. We elaborate on this trade‐off using graph theory, percolation theory and computational modeling of xylem. The results are validated using anatomical measurements of Acer branch xylem.Considering only species with vessels, increases in connectivity improve resistance to embolism spread without negatively affecting hydraulic conductivity. The often measured grouping index fails to capture the totality of the effect of conduit connectivity on xylem hydraulics.Variations in xylem network characteristics, such as conduit connectivity, might explain why hypothesized trends among woody species, such as the 'safety‐efficiency' trade‐off hypothesis, are weaker than expected. [ABSTRACT FROM AUTHOR]

Root hydraulic properties play a central role in the global water cycle, in agricultural systems productivity, and in ecosystem survival as they impact the canopy water supply. However, the existing experimental methods to quantify root hydraulic conductivities, such as the root pressure probing, are particularly challenging, and their applicability to thin roots and small root segments is limited. Therefore, there is a gap in methods enabling easy estimations of root hydraulic conductivities in diverse root types. Here, we present a new pipeline to quickly estimate root hydraulic conductivities across different root types, at high resolution along root axes. Shortly, free‐hand root cross‐sections were used to extract a selected number of key anatomical traits. We used these traits to parametrize the Generator of Root Anatomy in R (GRANAR) model to simulate root anatomical networks. Finally, we used these generated anatomical networks within the Model of Explicit Cross‐section Hydraulic Anatomy (MECHA) to compute an estimation of the root axial and radial hydraulic conductivities (kx and kr, respectively). Using this combination of anatomical data and computational models, we were able to create a root hydraulic conductivity atlas at the root system level, for 14‐day‐old pot‐grown Zea mays (maize) plants of the var. B73. The altas highlights the significant functional variations along and between different root types. For instance, predicted variations of radial conductivity along the root axis were strongly dependent on the maturation stage of hydrophobic barriers. The same was also true for the maturation rates of the metaxylem vessels. Differences in anatomical traits along and across root types generated substantial variations in radial and axial conductivities estimated with our novel approach. Our methodological pipeline combines anatomical data and computational models to turn root cross‐section images into a detailed hydraulic atlas. It is an inexpensive, fast, and easily applicable investigation tool for root hydraulics that complements existing complex experimental methods. It opens the way to high‐throughput studies on the functional importance of root types in plant hydraulics, especially if combined with novel phenotyping techniques such as laser ablation tomography. [ABSTRACT FROM AUTHOR]

In land surface models (LSMs), the hydraulic properties of the subsurface are commonly estimated according to the texture of soils at the Earth's surface. This approach ignores macropores, fracture flow, heterogeneity, and the effects of variable distribution of water in the subsurface on effective watershed‐scale hydraulic variables. Using hydrograph recession analysis, we empirically constrain estimates of watershed‐scale effective hydraulic conductivities (K) and effective drainable aquifer storages (S) of all reference watersheds in the conterminous United States for which sufficient streamflow data are available (n = 1,561). Then, we use machine learning methods to model these properties across the entire conterminous United States. Model validation results in high confidence for estimates of log(K) (r2 > 0.89; 1% < bias < 9%) and reasonable confidence for S (r2 > 0.83; −70% < bias < −18%). Our estimates of effective K are, on average, two orders of magnitude higher than comparable soil‐texture‐based estimates of average K, confirming the importance of soil structure and preferential flow pathways at the watershed scale. Our estimates of effective S compare favorably with recent global estimates of mobile groundwater and are spatially heterogeneous (5–3,355 mm). Because estimates of S are much lower than the global maximums generally used in LSMs (e.g., 5,000 mm in Noah‐MP), they may serve both to limit model spin‐up time and to constrain model parameters to more realistic values. These results represent the first attempt to constrain estimates of watershed‐scale effective hydraulic variables that are necessary for the implementation of LSMs for the entire conterminous United States. Plain Language Summary: Modeling the flow of water out of the ground and into streams requires extensive data that describe the hydraulic properties of the ground, including how much water is available to support streamflow (i.e., the volume of mobile groundwater) and how quickly that water may flow through the materials where it is stored (i.e., effective hydraulic conductivity). Currently, most large‐scale numerical models derive estimates of these properties from maps of soil types. These methods are known to be prone to error in many landscapes where bedrock fractures or biological activity (e.g., earthworm tunnels or rotted tree roots) are common, as these structural features may alter the effective properties of the subsurface by several orders of magnitude. To address these shortfalls, we provide empirical estimates of these properties through analysis of historical streamflow and make these data available at the continental scale for the first time. Key Points: Provide empirical estimates of watershed‐scale effective hydraulic variables for the continental United States for the first timeWatershed‐scale effective hydraulic conductivities are order(s) of magnitude higher than soil‐texture‐based estimates of average hydraulic conductivitiesMaximum drainable storage volumes may be used to realistically constrain models and reduce model spin‐up time [ABSTRACT FROM AUTHOR]

Summary: Eastern Australia was subject to its hottest and driest year on record in 2019. This extreme drought resulted in massive canopy die‐back in eucalypt forests. The role of hydraulic failure and tree size on canopy die‐back in three eucalypt tree species during this drought was examined.We measured pre‐dawn and midday leaf water potential (Ψleaf), per cent loss of stem hydraulic conductivity and quantified hydraulic vulnerability to drought‐induced xylem embolism. Tree size and tree health was also surveyed.Trees with most, or all, of their foliage dead exhibited high rates of native embolism (78–100%). This is in contrast to trees with partial canopy die‐back (30–70% canopy die‐back: 72–78% native embolism), or relatively healthy trees (little evidence of canopy die‐back: 25–31% native embolism). Midday Ψleaf was significantly more negative in trees exhibiting partial canopy die‐back (−2.7 to −6.3 MPa), compared with relatively healthy trees (−2.1 to −4.5 MPa). In two of the species the majority of individuals showing complete canopy die‐back were in the small size classes.Our results indicate that hydraulic failure is strongly associated with canopy die‐back during drought in eucalypt forests. Our study provides valuable field data to help constrain models predicting mortality risk. [ABSTRACT FROM AUTHOR]

Summary: Tropical ecosystems have the highest levels of biodiversity, cycle more water and absorb more carbon than any other terrestrial ecosystem on Earth. Consequently, these ecosystems are extremely important components of Earth's climatic system and biogeochemical cycles. Plant hydraulics is an essential discipline to understand and predict the dynamics of tropical vegetation in scenarios of changing water availability. Using published plant hydraulic data we show that the trade‐off between drought avoidance (expressed as deep‐rooting, deciduousness and capacitance) and hydraulic safety (P50 – the water potential when plants lose 50% of their maximum hydraulic conductivity) is a major axis of physiological variation across tropical ecosystems. We also propose a novel and independent axis of hydraulic trait variation linking vulnerability to hydraulic failure (expressed as the hydraulic safety margin (HSM)) and growth, where inherent fast‐growing plants have lower HSM compared to slow‐growing plants. We surmise that soil nutrients are fundamental drivers of tropical community assembly determining the distribution and abundance of the slow‐safe/fast‐risky strategies. We conclude showing that including either the growth‐HSM or the resistance‐avoidance trade‐off in models can make simulated tropical rainforest communities substantially more vulnerable to drought than similar communities without the trade‐off. These results suggest that vegetation models need to represent hydraulic trade‐off axes to accurately project the functioning and distribution of tropical ecosystems. [ABSTRACT FROM AUTHOR]

Recently, a novel approach with excellent performance based on the concept of the characteristic infiltration time, the characteristic time method (CTM), is proposed to infer soil sorptivity (S) and saturated hydraulic conductivity (Ks) from one‐dimensional (1D) cumulative infiltration. The current work provides a simplified version of the CTM, called the SCTM, by eliminating the necessity of the iteration method used in CTM and providing a similar accuracy as the original method when estimating S and Ks. We used both synthetic and experimental data to evaluate SCTM in comparison with the original CTM, as well as Sharma (SH) and curve‐fitting methods. In the case of synthetically simulated infiltration experiments, the predicted S and Ks values showed an excellent agreement with their theoretical values, with Nash–Sutcliffe (E) values higher than 0.9 and RMSE values of 0.11 cm h1/2 and 0.35 cm h–1, respectively. In the case of experimental data, the SCTM showed E values larger than 0.73 and RMSE values of 0.64 cm h1/2 and 0.35 cm h–1, respectively. The accuracy and the robustness of SCTM was comparable with the original CTM when applied on synthetic infiltration curves as well as on experimental data. Similar to the original CTM, the simplified approach also does not require the knowledge of the time validity, which is needed when using approaches based on Philip's infiltration theory. The method is applicable to infiltrations with durations from 15 min to 24 h. The supplemental material presents the calculation of S and Ks using SCTM in an Excel spreadsheet. Core Ideas: A simplified version of the CTM is proposed to estimate the S and Ks from a 1D infiltration curve.The SCTM is nearly as accurate as the original CTM in prediction of S and Ks.The SCTM eliminates the necessity of the iteration method used in original CTM. [ABSTRACT FROM AUTHOR]

SUMMARY: The leaf vascular bundle sheath cells (BSCs) that tightly envelop the leaf veins, are a selective and dynamic barrier to xylem sap water and solutes radially entering the mesophyll cells. Under normal conditions, xylem sap pH below 6 is presumably important for driving and regulating the transmembranal solute transport. Having discovered recently a differentially high expression of a BSC proton pump, AHA2, we now test the hypothesis that it regulates the xylem sap pH and leaf radial water fluxes. We monitored the xylem sap pH in the veins of detached leaves of wild‐type Arabidopsis, AHA mutants and aha2 mutants complemented with AHA2 gene solely in BSCs. We tested an AHA inhibitor (vanadate) and stimulator (fusicoccin), and different pH buffers. We monitored their impact on the xylem sap pH and the leaf hydraulic conductance (Kleaf), and the effect of pH on the water osmotic permeability (Pf) of isolated BSCs protoplasts. We found that AHA2 is necessary for xylem sap acidification, and in turn, for elevating Kleaf. Conversely, AHA2 knockdown, which alkalinized the xylem sap, or, buffering its pH to 7.5, reduced Kleaf, and elevating external pH to 7.5 decreased the BSCs Pf. All these showed a causative link between AHA2 activity in BSCs and leaf radial hydraulic water conductance. [ABSTRACT FROM AUTHOR]

Saturated hydraulic conductivity (Ksat) is a key soil hydraulic parameter for representing infiltration and drainage in land surface models. For large scale applications, Ksat is often estimated from pedotransfer functions (PTFs) based on easy‐to‐measure soil properties like soil texture and bulk density. The reliance of PTFs on data from uniform arable lands and the omission of soil structure limits the applicability of texture‐based predictions of Ksat in vegetated lands. To include effects of terrain, climate, and vegetation in the derivation of a new global Ksat map at 1 km resolution, we harness technological advances in machine learning and availability of remotely sensed surrogate information. For model training and testing, a global compilation of 6,814 geo‐referenced Ksat measurements from the literature was used. The accuracy assessment based on spatial cross‐validation shows a concordance correlation coefficient (CCC) of 0.16 and a root mean square error (RMSE) of 1.18 for log10 Ksat values in cm/day (CCC = 0.79 and RMSE = 0.72 for non‐spatial cross‐validation). The generated maps of Ksat represent spatial patterns of soil formation processes more distinctly than previous global maps of Ksat based on easy‐to‐measure soil properties. The validation of the model indicates that Ksat could be modeled without bias using Covariate‐based GeoTransfer Functions (CoGTFs) that harness spatially distributed surface and climate attributes, compared to soil information based PTFs. The relatively poor performance of all models in the validation (low CCC and high RMSE) highlights the need for the collection of additional Ksat values to train the model for regions with sparse data. Plain Language Summary: The soil saturated hydraulic conductivity (Ksat) defines how fast water infiltrates into and percolates through the soil. To model water flow at large scales, accurate maps of Ksat are needed. Usually, Ksat is not measured directly but deduced from well‐known basic soil properties (e.g., soil texture, bulk density). However, these estimates neglect the influence of vegetation and climate on formation of soil structures that control Ksat. To improve global predictions of Ksat, we use a new spatially referenced Ksat data collection and apply machine learning to exploit correlations between Ksat and other properties (e.g., soil information, terrain, climate, and vegetation). These correlations are then implemented at global scale using maps of all relevant properties (so called "environmental covariates") that were measured by remote sensing. We call this new approach to predictive Ksat mapping "Covariate‐based GeoTransfer Function" (CoGTF) to highlight differences with other maps that neglect spatial correlation with soil formation processes and that are based only on soil data (so called "pedotransfer functions", PTFs). We show that the new maps based on CoGTF perform better than approaches based on PTFs. Key Points: Climate, vegetation, and terrain affect spatial patterns of saturated hydraulic conductivity (Ksat)The effect of these environmental covariates on Ksat is quantified using remote sensing data and machine learningWe introduce Covariate‐based GeoTransfer Functions to improve Ksat predictions based on pedotransfer functions [ABSTRACT FROM AUTHOR]

Summary: The evolution of angiosperms was accompanied by the segregation and specialisation of their xylem tissues. This study aimed to determine whether the fraction and arrangement of parenchyma tissue influence the hydraulic efficiency–safety trade‐off in the basal angiosperms.We examined xylem anatomical structure and hydraulic functioning of 28 woody species of Magnoliids in a tropical rainforest of Madagascar and reported, for the first time, quantitative measurements that support the relationship between vessel‐to‐xylem parenchyma connectivity and the hydraulic efficiency–safety trade‐off. We also introduced a new measurement – the distance of species from the trade‐off limit – to quantify the co‐optimisation of hydraulic efficiency and safety.Although the basal angiosperms in this study had low hydraulic conductivity and safety, species with higher axial parenchyma fraction (APf) had significantly higher hydraulic conductivity. Hydraulic efficiency–safety optimisation was accompanied by higher APf and vessel‐to‐axial parenchyma connectivity. Conversely, species exhibiting high ray parenchyma fraction and high vessel‐to‐ray connectivity had lower Ks and were further away from the hydraulic trade‐off limit line.Our results provide evidence that axial parenchyma fraction and paratracheal arrangement are associated with both enhanced hydraulic efficiency and safety. [ABSTRACT FROM AUTHOR]

We present an upscaled Lagrangian approach to predict the plume evolution in highly heterogeneous aquifers. The model is parameterized by transport‐independent characteristics such as the statistics of hydraulic conductivity and the Eulerian flow speed. It can be conditioned on the tracer properties and flow data at the injection region. Thus, the model is transferable to different solutes and hydraulic conditions. It captures the large‐scale non‐Gaussian features for the evolution of the longitudinal mass distribution observed for the bromide and tritium tracer plumes at the Macrodispersion Experiment (MADE) site (Columbus, Mississippi, USA), which are characterized by a slow moving peak and pronounced forward tailing. These large‐scale features are explained by advective tracer propagation due to a broad distribution of spatially persistent Eulerian flow speeds as a result of spatial variability in hydraulic conductivity. Plain Language Summary: The prediction of solute transport in highly heterogeneous porous media has been a long‐standing question. We propose an approach that predicts and explains observed tracer distributions in terms of medium and flow heterogeneity. The model is parameterized by the statistical characteristics of hydraulic conductivity, distribution of flow speeds, porosity, and retardation coefficient, that is, transport‐independent parameters. This study gives new insight for the understanding and prediction of large‐scale tracer dispersion in heterogeneous aquifers. Key Points: A predictive model for tracer dispersion in highly heterogeneous aquifers is presentedThe model is parameterized by transport‐independent parametersThe large‐scale evolution of the tracer profiles of the MADE‐1 and MADE‐2 experiments is predicted [ABSTRACT FROM AUTHOR]

Summary: Amazonian droughts are increasing in frequency and severity. However, little is known about how this may influence species‐specific vulnerability to drought across different ecosystem types.We measured 16 functional traits for 16 congeneric species from six families and eight genera restricted to floodplain, swamp, white‐sand or plateau forests of Central Amazonia. We investigated whether habitat distributions can be explained by species hydraulic strategies, and if habitat specialists differ in their vulnerability to embolism that would make water transport difficult during drought periods.We found strong functional differences among species. Nonflooded species had higher wood specific gravity and lower stomatal density, whereas flooded species had wider vessels, and higher leaf and xylem hydraulic conductivity. The P50 values (water potential at 50% loss of hydraulic conductivity) of nonflooded species were significantly more negative than flooded species. However, we found no differences in hydraulic safety margin among species, suggesting that all trees may be equally likely to experience hydraulic failure during severe droughts.Water availability imposes a strong selection leading to differentiation of plant hydraulic strategies among species and may underlie patterns of adaptive radiation in many tropical tree genera. Our results have important implications for modeling species distribution and resilience under future climate scenarios. [ABSTRACT FROM AUTHOR]

Premise: Photosynthetic stems represent a source of extra carbon in plants from hot and dry environments, but little is known about how leaves and photosynthetic stems differ in terms of photosynthetic capacity, trait coordination, and responses to seasonal drought in subtropical systems. Methods: We studied photosynthetic, hydraulic, morphometric (specific leaf area [SLA], wood density [WD]), and biochemical (C and N isotopes) traits in leaves and photosynthetic stems of 12 plant species from a sarcocaulescent scrub in the southern Baja California Peninsula, Mexico, in wet and dry seasons. Results: Leaves and stems had similar mean photosynthetic capacity, as evaluated by chlorophyll fluorescence traits, indicating similar investment in leaf and stem photosynthesis. We did not find a relationship between stem hydraulic conductivity and leaf or stem photosynthetic traits. However, we found resource allocation trade‐offs, between WD and both stem hydraulic conductivity and SLA. Leaf and stem photosynthetic traits did not change with season, but specific stem area was one of the few traits that changed the most between seasons—it increased during the dry season by as much as 154% indicating substantial water storage. Conclusions: Our results indicate the same proportional investment in photosynthetic capacity and dry matter in both leaves and photosynthetic stems across all 12 species. We identified multiple strategies at this seasonal site, with species ranging from high WD, low SLA, low hydraulic conductivity, and high specific bark area on one end of the spectrum and opposite traits on the other end. [ABSTRACT FROM AUTHOR]

Premise: The young seedling life stage is critical for reforestation after disturbance and for species migration under climate change, yet little is known regarding their basic hydraulic function or vulnerability to drought. Here, we sought to characterize responses to desiccation including hydraulic vulnerability, xylem anatomical traits, and impacts on other stem tissues that contribute to hydraulic functioning. Methods: Larix occidentalis, Pseudotsuga menziesii, and Pinus ponderosa (all ≤6 weeks old) were imaged using x‐ray computed microtomography during desiccation to assess seedling biomechanical responses with concurrently measured hydraulic conductivity (ks) and water potential (Ψ) to assess vulnerability to xylem embolism formation and other tissue damage. Results: In non‐stressed samples for all species, pith and cortical cells appeared circular and well hydrated, but they started to empty and deform with decreasing Ψ which resulted in cell tearing and eventual collapse. Despite the severity of this structural damage, the vascular cambium remained well hydrated even under the most severe drought. There were significant differences among species in vulnerability to xylem embolism formation, with 78% xylem embolism in L. occidentalis by Ψ of −2.1 MPa, but only 47.7% and 62.1% in P. ponderosa and P. menziesii at −4.27 and −6.73 MPa, respectively. Conclusions: Larix occidentalis seedlings appeared to be more susceptible to secondary xylem embolism compared to the other two species, but all three maintained hydration of the vascular cambium under severe stress, which could facilitate hydraulic recovery by regrowth of xylem when stress is relieved. [ABSTRACT FROM AUTHOR]

Summary: Plasma membrane intrinsic proteins (PIPs) are known to be major facilitators of the movement of a number of substrates across cell membranes. From a drought‐resistant cultivar of Oryza sativa (rice), we isolated an OsPIP1;3 gene single‐nucleotide polymorphism (SNP) that is mostly expressed in rice roots and is strongly responsive to drought stress. Immunocytochemistry showed that OsPIP1;3 majorly accumulated on the proximal end of the endodermis and the cell surface around the xylem. Expression of GFP‐OsPIP1;3 alone in Xenopus oocytes or rice protoplasts showed OsPIP1;3 mislocalization in the endoplasmic reticulum (ER)‐like neighborhood, whereas co‐expression of OsPIP2;2 recruited OsPIP1;3 to the plasma membrane and led to a significant enhancement of water permeability in oocytes. Moreover, reconstitution of 10×His‐OsPIP1;3 in liposomes demonstrated water channel activity, as revealed by stopped‐flow light scattering. Intriguingly, by patch‐clamp technique, we detected significant NO3− conductance of OsPIP1;3 in mammalian cells. To investigate the physiological functions of OsPIP1;3, we ectopically expressed the OsPIP1;3 gene in Nicotiana benthamiana (tobacco). The transgenic tobacco plants exhibited higher photosynthesis rates, root hydraulic conductivity (Lpr) and water‐use efficiency, resulting in a greater biomass and a higher resistance to water deficit than the wild‐type did. Further experiments suggested that heterologous expression of OsPIP1;3 in cyanobacterium altered bacterial growth under different conditions of CO2 gas supply. Overall, besides shedding light on the multiple functions played by OsPIP1;3, this work provides insights into the translational value of plant AQPs. Significance Statement: We detected water, CO2 and nitrate transport abilities of rice OsPIP1;3 using different technical approaches. Ectopic expression of the OsPIP1;3 gene in tobacco substantially enhanced plant growth and resistance to water deficit by increasing the photosynthesis rate and root hydraulic conductivity in transgenic plants. This study provides important clues for uncovering the multiple functions played by plant PIP proteins and the related translational value. [ABSTRACT FROM AUTHOR]

Summary: Xylem anatomy and function have large implications for plant growth as well as survival during drought, but the impact of nutrient limitation on xylem is not fully understood. This study examines the pygmy forest in California, a plant community that experiences negligible water stress but is severely stunted by low‐nutrient and acidic soil, to investigate how nutrient limitation affects xylem function.Thirteen key anatomical and hydraulic traits of stems of four species were compared between pygmy forest plants and nearby conspecifics growing on richer soil.Resistance to cavitation (P50), a critical trait for predicting survival during drought, had highly species‐specific responses: in one species, pygmy plants had a 26% decrease in cavitation resistance compared to higher‐nutrient conspecifics, while in another species, pygmy plants had a 56% increase in cavitation resistance. Other traits responded to nutrient limitation more consistently: pygmy plants had smaller xylem conduits and higher leaf‐specific conductivity (KL) than conspecific controls.Edaphic stress, even in the absence of water stress, altered xylem structure and thus had substantial impacts on water transport. Importantly, nutrient limitation shifted cavitation resistance in a species‐specific and unpredictable manner; this finding has implications for the assessment of cavitation resistance in other natural systems. [ABSTRACT FROM AUTHOR]

Hydraulic fracturing is an effective way to exploit hydrocarbons in tight oil reservoir. The success of this technique lies on the creation of high conductivity channels for the oil and gas. Quantitative analysis of factors influencing the conductivity of propped fractures is significant for the design of the operation schedule. According to the definition of sphericity, cylindrical and planar proppants of different sphericity and sizes were presented. And disordered packs of nonspherical proppants in fractures of different widths were established by the discrete element method. The change of the proppant embedment and fracture width under different closure pressures were analyzed by the solid mechanics. During the fracture deformation, the pressure and velocity of the fluid flowing in fractures were simulated by Lattice‐Boltzmann method. Based on that, the effect of the proppant size, sphericity, and the fracture width on the permeability and conductivity of hydraulic fractures were investigated. The accuracy of the model was verified by the experimental data. The simulation results show that the fracture permeability and conductivity decrease with the decrease in the rock's Young's modulus, proppant size, and sphericity, and their stress sensitivity increases with the decrease in the rock's Young's modulus and the increase in the proppant size. Increasing fracture width can improve fracture conductivity more significantly than increasing fracture permeability. The permeability and conductivity of the fractures filled cylindrical proppants are higher than that of the fractures filled with planar proppants. [ABSTRACT FROM AUTHOR]

Summary: Determining physiological mechanisms and thresholds for climate‐driven tree die‐off could help improve global predictions of future terrestrial carbon sinks. We directly tested for the lethal threshold in hydraulic failure – an inability to move water due to drought‐induced xylem embolism – in a pine sapling experiment.In a glasshouse experiment, we exposed loblolly pine (Pinus taeda) saplings (n = 83) to drought‐induced water stress ranging from mild to lethal. Before rewatering to relieve drought stress, we measured native hydraulic conductivity and foliar color change. We monitored all measured individuals for survival or mortality.We found a lethal threshold at 80% loss of hydraulic conductivity – a point of hydraulic failure beyond which it is more likely trees will die, than survive, and describe mortality risk across all levels of water stress. Foliar color changes lagged behind hydraulic failure – best predicting when trees had been dead for some time, rather than when they were dying.Our direct measurement of native conductivity, while monitoring the same individuals for survival or mortality, quantifies a continuous probability of mortality risk from hydraulic failure. Predicting tree die‐off events and understanding the mechanism involved requires knowledge not only of when trees are dead, but when they begin dying – having passed the point of no return. [ABSTRACT FROM AUTHOR]