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Introduction: Reduced water content in the soil triggers physiological, biochemical, and morphological damage to plants, aggravated by nutritional deficiency. One possible strategy to mitigate this damage comprises the use of silicon (Si). This study investigated whether Si can mitigate the damage caused by water deficit through nutritional mechanisms in bean plants grown under field conditions. Furthermore, it investigated whether the effectiveness of Si is influenced by water availability in the soil and the Si dose supplied. Methods: Therefore, two split-plot experiments were carried out: with and without K supply. In both experiments,the treatments comprised a 3 x 4 factorial scheme. Treatments included three water regimes: 80% (no water deficit), 60% (moderate water deficit), and 40% (severe water deficit) of the soil's water retention capacity. Moreover, they comprised four doses of Si supplied via fertigation-0 kg/ha, 4 kg/ha, 8 kg/ha, and 12 kg/ha-arranged in a randomized block design with four replications. Results and discussion: The appropriate dose of Si to be applied increased with the severity of the water deficit, with the recommended dose being 6 kg/ha, 7 kg/ha, and 8 kg/ha of Si for adequate water conditions, moderate water deficit, and severe water deficit, respectively. [ABSTRACT FROM AUTHOR]

The two most important abiotic plant stressors that impact plant development and crop yields are water stress and salinity stress. These issues are particularly important in arid and semi‐arid regions. According to a 2019 research paper, “thirty crop species provide 90% of our food, most of which display severe yield losses under moderate salinity.” Moderate salinity is defined as extracted pore‐water salinity in the range of 4–8 dS m−1. Currently, commercially available soil moisture and bulk soil electrical conductivity sensors can estimate in situ soil pore‐water electrical conductivity with suitably calibrated soil moisture and electrical conductivity models for a wide range of soil types and growing media. With knowledge of the pore‐water electrical conductivity it is possible to estimate osmotic tension. Furthermore, there are commercially available dielectric tensiometers that provide soil water tension measurements from the water content of a porous matrix component that is in equilibrium with the water capillary forces in the surrounding soil or growing media. Combining soil moisture and soil water tension measurements enables water retention curves and the hydraulic properties of a soil to be determined. However, the overall ability of a plant to extract water from a soil or substrate is typically dominated by water tension and osmotic tension. Currently, while the technology blocks exist in different commercial offerings, the combination of a water tension and osmotic tension in an integrated sensor does not exist. A key benefit of the porous matrix in a dielectric tensiometer is that electrical measurements include a component of extracted water from the soil or growing media. With the appropriate dielectric characterization of the porous matrix, there should be no need for soil‐specific calibrations. The aim of the paper is to outline the measurement processing that could be implemented into an integrated water tension and osmotic tension sensor. [ABSTRACT FROM AUTHOR]

Introduction: Soil drought during summer in Central Europe has become more frequent and severe over the last decades. European forests are suffering increasing damage, particularly Norway spruce. Douglas-fir (Pseudotsuga menziesii (Mirbel) Franco), a non-native tree species, is considered as a promising alternative to build drought-resilient forests. The main goal of this study was to investigate the intraannual radial stem growth and sap flow performance of Douglas-fir along a precipitation gradient across Germany under severe drought. Material and methods: Sap flow and stem radial changes of up to ten trees each at four sites with different precipitation regimes were measured in combination with volumetric soil water content during the growing season of 2022. Measurements of stem radial changes were used to calculate the trees' stem water deficit, a proxy for tree water status and drought stress. Results: The severe summer drought of 2022 led to an early growth cessation and a significant reduction in daily sap flow at all four sites monitored. We could identify a site-specific threshold in soil water availability ranging between 21.7 and 29.6% of relative extractable water (REW) under which stem water reserves cannot be replenished and thereby inhibiting radial growth. We could also demonstrate that at this threshold, sap flow is heavily reduced to between 43.5 and 53.3%, and for a REW below 50%, sap flow linearly decreases by 1.1-2.0% per 1% reduction in REW. This reduction tends to follow the humidity gradient, being more pronounced at the most oceanic characterized site and suggesting an adaptation to site conditions. Even though Douglas-fir is considered to be more drought stress resistant than Norway spruce, growth and sap flow are greatly reduced by severe summer drought, which became more frequent in recent years and their frequency and intensity is likely to increase. Conclusions: Our results suggest that timber production of Douglas-fir in Central Europe will decline considerably under projected climate change, and thus pointing to site specific growth constraints for a so far promising non-native tree species in Europe. [ABSTRACT FROM AUTHOR]

The development of water-saving management relies on understanding the physiological response of crops to soil drought. The coordinated regulation of hydraulics and stomatal conductance in plant water relations has steadily received attention. However, research focusing on grain crops, such as winter wheat, remains limited. In this study, three soil water supply treatments, including high (H), moderate (M), and low (L) soil water contents, were conducted with potted winter wheat. Leaf water potential (Ψleaf), leaf hydraulic conductance (Kleaf), and stomatal conductance (gs), as well as leaf biochemical parameters and stomatal traits were measured. Results showed that, compared to H, predawn leaf water potential (ΨPD) significantly reduced by 48.10% and 47.91%, midday leaf water potential (ΨMD) reduced by 40.71% and 43.20%, Kleaf reduced by 64.80% and 65.61%, and gs reduced by 21.20% and 43.41%, respectively, under M and L conditions. Although gs showed a significant difference between M and L, Ψleaf and Kleaf did not show significant differences between these treatments. The maximum carboxylation rate (Vcmax) and maximum electron transfer rate (Jmax) under L significantly decreased by 23.11% and 28.10%, stomatal density (SD) and stomatal pore area index (SPI) under L on the abaxial side increased by 59.80% and 52.30%, respectively, compared to H. The leaf water potential at 50% hydraulic conduction loss (P50) under L was not significantly reduced. The gs was positively correlated with ΨMD and Kleaf, but it was negatively correlated with abscisic acid (ABA) and SD. A threshold relationship between gs and Kleaf was observed, with rapid and linear reduction in gs occurring only when Kleaf fell below 8.70 mmol m−2 s−1 MPa−1. Our findings demonstrate that wheat leaves adapt stomatal regulation strategies from anisohydric to isohydric in response to reduced soil water content. These results enrich the theory of trade-offs between the carbon assimilation and hydraulic safety in crops and also provide a theoretical basis for water management practices based on stomatal regulation strategies under varying soil water conditions. [ABSTRACT FROM AUTHOR]

Peruvian watergrass (Luziola peruviana J.F. Gmel.) is a perennial weed often found in paddy fields in the southern region of Brazil. Its chemical control is performed mainly by herbicides such as glyphosate in burndown, whose efficacy depends on soil moisture. Under excess‐water soil conditions, glyphosate efficacy is reduced, probably due to reduced translocation and the involvement of photoassimilates partition. Furthermore, little is known about the stress tolerance of these plants subjected to water deficit. Based on that, we performed experiments to verify the effect of soil moisture on the biochemical parameters of Peruvian watergrass and glyphosate translocation to the stolon and roots. Total soluble sugars, sucrose, starch, and glyphosate concentrations in leaves, culms, roots, and glyphosate partitioning were quantified. The malondialdehyde content and the lipid peroxidation increased with the drainage. Under drainage conditions, superoxide production was higher in roots than leaves, while peroxide production was lower in roots than leaves. The electrolyte leakage increased with the drainage and glyphosate application. The total soluble sugar content varied in each organ with a significant increase in the culm 14 days after application in the draining treatment. Sucrose varied considerably and reached its maximum concentration at 21 days after herbicide application. The starch accumulation in the culm was 7 days after applying the highest glyphosate dose. The presence of glyphosate in the roots subjected to soil drainage indicates the movement of this herbicide. In conclusion, soil drainage profoundly impacts Peruvian watergrass physiology, increasing the photoassimilates and glyphosate translocation to the stolon and root. This explains why glyphosate efficacy is higher under drainage conditions. [ABSTRACT FROM AUTHOR]

Summary: Some plants exhibit dynamic hydraulic regulation, in which the strictness of hydraulic regulation (i.e. iso/anisohydry) changes in response to environmental conditions. However, the environmental controls over iso/anisohydry and the implications of flexible hydraulic regulation for plant productivity remain unknown.In Juniperus osteosperma, a drought‐resistant dryland conifer, we collected a 5‐month growing season time series of in situ, high temporal‐resolution plant water potential (Ψ) and stand gross primary productivity (GPP). We quantified the stringency of hydraulic regulation associated with environmental covariates and evaluated how predawn water potential contributes to empirically predicting carbon uptake.Juniperus osteosperma showed less stringent hydraulic regulation (more anisohydric) after monsoon precipitation pulses, when soil moisture and atmospheric demand were high, and corresponded with GPP pulses. Predawn water potential matched the timing of GPP fluxes and improved estimates of GPP more strongly than soil and/or atmospheric moisture, notably resolving GPP underestimation before vegetation green‐up.Flexible hydraulic regulation appears to allow J. osteosperma to prolong soil water extraction and, therefore, the period of high carbon uptake following monsoon precipitation pulses. Water potential and its dynamic regulation may account for why process‐based and empirical models commonly underestimate the magnitude and temporal variability of dryland GPP. [ABSTRACT FROM AUTHOR]

Understanding soil moisture variability and estimating high‐resolution soil moisture at subfield to field scales is critical for agricultural research and applications. However, systematic investigation of subfield scale soil moisture variability over cropland is still lacking from both measurement and satellite remote sensing. In this study, we aim to investigate (1) the characteristics of within‐field soil moisture distribution over typical cropland in the US Midwest and (2) the capabilities of satellite remote sensing in capturing the spatiotemporal variabilities of soil moisture at subfield scale. Specifically, we conducted soil moisture field experiments in three typical commercial agricultural fields (∼85 acres per field) in central Illinois, representing typical commercial farmlands in the US Midwest, and compared the soil moisture measurements with satellite remote sensing data from optical and active microwave sensors. In each field, dense soil moisture samples (spaced at 50–60 m) were obtained for two dry down events in May and July 2021, and multiple long‐term soil moisture stations were installed. We found prominent time‐invariant spatial structures of soil moisture at within‐field scales both during the dry down period and over longer time scales, and the stability is minimally affected by plant water use during the growing season. Comparing the field campaign measurements with satellite remote sensing data, we found that surface reflectance of shortwave infrared bands, such as SWIR1 (1610 nm) from Sentinel‐2, can capture relative surface soil moisture patterns at within‐field scales, but their relationships with soil moisture are field specific. These findings and the improved understanding of within‐field soil moisture dynamics could potentially help future research on high‐resolution soil moisture estimation with multi‐source remote sensing data. Core Ideas: High‐density soil moisture sampling was conducted in agricultural fields.Time‐invariant spatial structures of within‐field soil moisture were evaluated.Strong but field‐specific relationships between soil moisture and optical remote sensing were found.A pathway for remote sensing based high‐resolution soil moisture estimation was proposed. [ABSTRACT FROM AUTHOR]

Water uptake by plant roots is an important component of the soil water balance. Predicting to what extent potential transpiration from the canopy, that is, transpiration demand, can be met by supply of water from the soil through the root system is crucial to simulate the actual transpiration and assess vegetation water stress. In models that simulate the dynamics of vertical soil water content profiles as a function of water fluxes and soil water potential gradients, the root water uptake (RWU) distribution is represented by macroscopic sink terms. We present RWU functions that calculate sink terms based on a mechanistic model of water flow in the soil–root system. Based on soil–root hydraulics, we define α‐supply functions representing the maximal uptake by the root system from a certain soil depth when the root collar water potential equals the wilting point, ω‐supply factors representing the maximal supply from the entire root system, and a critical ωc factor representing the potential transpiration demand. These functions and factors are subsequently used to calculate RWU distributions directly from potential transpiration or demand and the soil water potentials. Unlike currently used approaches, which define α‐stress functions and ω factors representing ratios of actual uptake to uptake demand, the supply‐based formulations can be derived directly from soil and root hydraulic properties and can represent processes like root hydraulic redistribution and hydraulic lift. Core Ideas: Functions to calculate root water uptake (RWU) from different soil depths were derived.RWU is calculated directly using soil water potentials and the potential transpiration rate.The functions are derived using soil and root hydraulic properties.Phenomena like RWU compensation, hydraulic redistribution, and hydraulic lift are reproduced.Similarities and differences with currently used uptake functions are discussed. [ABSTRACT FROM AUTHOR]

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Predicting soil water status remotely is appealing due to its low cost and large‐scale application. During drought, plants can disconnect from the soil, causing disequilibrium between soil and plant water potentials at pre‐dawn. The impact of this disequilibrium on plant drought response and recovery is not well understood, potentially complicating soil water status predictions from plant spectral reflectance. This study aimed to quantify drought‐induced disequilibrium, evaluate plant responses and recovery, and determine the potential for predicting soil water status from plant spectral reflectance. Two species were tested: sweet corn (Zea mays), which disconnected from the soil during intense drought, and peanut (Arachis hypogaea), which did not. Sweet corn's hydraulic disconnection led to an extended ‘hydrated’ phase, but its recovery was slower than peanut's, which remained connected to the soil even at lower water potentials (−5 MPa). Leaf hyperspectral reflectance successfully predicted the soil water status of peanut consistently, but only until disequilibrium occurred in sweet corn. Our results reveal different hydraulic strategies for plants coping with extreme drought and provide the first example of using spectral reflectance to quantify rhizosphere water status, emphasizing the need for species‐specific considerations in soil water status predictions from canopy reflectance. [ABSTRACT FROM AUTHOR]

During extensive periods without rain, known as dry-downs, decreasing soil moisture (SM) induces plant water stress at the point when it limits evapotranspiration, defining a critical SM threshold (θcrit). Better quantification of θcrit is needed for improving future projections of climate and water resources, food production, and ecosystem vulnerability. Here, we combine systematic satellite observations of the diurnal amplitude of land surface temperature (dLST) and SM during dry-downs, corroborated by in-situ data from flux towers, to generate the observation-based global map of θcrit. We find an average global θcrit of 0.19 m3/m3, varying from 0.12 m3/m3 in arid ecosystems to 0.26 m3/m3 in humid ecosystems. θcrit simulated by Earth System Models is overestimated in dry areas and underestimated in wet areas. The global observed pattern of θcrit reflects plant adaptation to soil available water and atmospheric demand. Using explainable machine learning, we show that aridity index, leaf area and soil texture are the most influential drivers. Moreover, we show that the annual fraction of days with water stress, when SM stays below θcrit, has increased in the past four decades. Our results have important implications for understanding the inception of water stress in models and identifying SM tipping points. Using systematic satellite observations of land surface temperature and soil moisture during soil dry-downs, the spatially-explicit global distribution of the critical soil moisture threshold of plant water stress and its drivers is uncovered. [ABSTRACT FROM AUTHOR]

Summary: Understanding the capacity of temperate trees to acclimate to limited soil water has become essential in the face of increasing drought risk due to climate change. We documented seasonal – or phenological – patterns in acclimation to water deficit stress in stems and leaves of tree species spanning the angiosperm phylogeny.Over 3 yr of field observations carried out in two US arboreta, we measured stem vulnerability to embolism (36 individuals of 7 Species) and turgor loss point (119 individuals of 27 species) over the growing season. We also conducted a growth chamber experiment on 20 individuals of one species to assess the mechanistic relationship between soil water restriction and acclimation.In three‐quarters of species measured, plants became less vulnerable to embolism and/or loss of turgor over the growing season. We were able to stimulate this acclimatory effect by withholding water in the growth chamber experiment.Temperate angiosperms are capable of acclimation to soil water deficit stress, showing maximum vulnerability to soil water deficits following budbreak and becoming more resilient to damage over the course of the growing season or in response to simulated drought. The species‐specific tempo and extent of this acclimatory potential constitutes preadaptive climate change resilience. [ABSTRACT FROM AUTHOR]

Aims: Arbuscular mycorrhizal fungi (AMF) play a crucial role in enhancing plant resistance to drought stress by improving the plant-water relationship. However, the precise mechanism of AMF-mediated water transport to host plant roots remains elusive. Methods: In a compartmentalized experiment comprising both plant and non-plant compartments, we employed heavy-oxygen water (18O-labeled) to directly trace and quantify the transport of water by AMF hyphae to alfalfa under the condition of high soil moisture (70% of the maximum field water holding capacity) and low soil moisture (40% of the maximum field water holding capacity). Results: Our findings revealed that irrespective of soil moisture levels, hyphae entering the 18O-labeled compartment (AM treatment) significantly enriched 18O in alfalfa transpiration water compared to no hyphae entering the 18O-labeled compartment (NM treatment). We calculated the direct water transport by AMF using a standard isotope mixing model, demonstrating that in high and low- moisture soil substrates, AM fungi contributed 12.32% and 17.03% of the total transpiration water, respectively. Conclusions: These results highlight that the direct transport of water from AMF hyphae to horticulture plants should not be underestimated in comparison to plant transpiration demand. Moreover, the water contribution of AM fungal hyphae to host plants is more significant in arid soil, especially in dry soil substrate. This underscores the critical role of mycelial water transport in supporting plant survival under water-limiting conditions. [ABSTRACT FROM AUTHOR]

Aims: Water-absorbing polymer (WAP) is recognized as a suitable soil additive for enhancing water retention and storage in the root zone under arid condition. The presence of such additives may alter the soil water characteristic curve (SWCC) and hence, may affect the plant growth. The effect of WAP on SWCC particularly, with the presence of vegetation is rarely explored. Therefore, this study investigates the combined influence of WAP and vegetation on SWCC for unraveling the soil-plant-WAP-atmosphere interaction. Methods: Two different WAPs along with vegetation species Solanum Lycopersicum species, were considered. The SWCCs along with its model parameters (Air entry value (AEV); Plant available water content (PAWC), FC (Field Capacity) and Permanent Wilting Point (PWP)) were established for silty loamy soil considering the different combinations of WAPs and vegetation. The changes in root structure were analysed with and without the presence of WAP. Results: Parameters such as FC, PWP and PAWC are increased by more than 1.5 times with the presence of WAP and vegetation compared to control soil This is mainly attributed to the alteration in pore volume in the soil matrix. Root-induced soil showed higher moisture retention than control soil at a specific suction which is affected by the root biomass/architecture. Conclusions: The study indicates that the WAP helps to reduce water demand during arid condition. This study also demonstrates the usefulness of SWCC as a tool to unravel the combined influence of WAP and vegetation on soil-water storage and water retention characteristics of soil associated with soil-WAP-root-atmosphere interaction. [ABSTRACT FROM AUTHOR]

In this study, three typical plants capable of restoring in the Heidaigou open-pit mine dump, namely, Pinus sylvestris var. mongolica, Caragana korshinskii, and Medicago sativa, were taken as the research objects. The δ2H and δ18O values of atmospheric precipitation, soil water, stem water, and leaf water were measured using the stable isotope technique, and the distribution characteristics of the δ2H and δ18O values of different water sources were identified. The IsoSource model (version1.3.1) was used to calculate the contribution rate of different water sources to the plants, and the differences and dynamic changes in the water sources for P. sylvestris var. mongolica, C. korshinskii, and M. sativa during the rainy season were examined. Results showed that the water source of the three plants was found to be mainly soil water, and the utilization of each potential water source varied in different periods of the rainy season. In June, when SWC was sufficient, P. sylvestris var. mongolica and M. sativa primarily absorbed and utilized shallow and middle soil water, with relative utilization ratios of 55.5% and 59%, respectively, while C. korshinskii has a more balanced utilization ratio of soil water in each layer, with shallow soil water utilization at 33.7%, middle soil water at 34.2%, and deep soil water at 32.2%. In August, when SWC decreased, P. sylvestris var. mongolica, C. korshinskii, and M. sativa were all transferred to deep soil water, with utilization ratios of 75.8%, 78.8%, and 71.1%, respectively. The values showed that these three typical plants are capable of restoring can respond to external water changes through the plastic transformation of water absorption sources. Among them, C. korshinskii can flexibly use soil water in each layer, has stronger survival competitiveness in drought, and can better adapt to the fragile ecological environment of a mining dump. [ABSTRACT FROM AUTHOR]

Agriculture, a vital element of human survival, confronts challenges of meeting rising demand due to population growth and product availability in developing nations. Reliance on pesticides and fertilizers strains natural resources, leading to soil degradation and water scarcity. Addressing these issues necessitates enhancing water efficiency in agriculture. Polymeric hydrogels, with their unique water retention and nutrient-release capabilities, offer promising solutions. These superabsorbent materials form three-dimensional networks retaining substantial amounts of water. Their physicochemical properties suit various applications, including agriculture. Production involves methods like bulk, solution, and suspension polymerization, with cross-linking, essential for hydrogels, achieved through physical or chemical means, each with different advantages. Grafting techniques incorporate functional groups into matrices, while radiation synthesis offers purity and reduced toxicity. Hydrogels provide versatile solutions to tackle water scarcity and soil degradation in agriculture. Recent research explores hydrogel formulations for optimal agricultural performance, enhancing soil water retention and plant growth. This review aims to offer a comprehensive overview of hydrogel technologies as adaptable solutions addressing water scarcity and soil degradation challenges in agriculture, with ongoing research refining hydrogel formulations for optimal agricultural use. [ABSTRACT FROM AUTHOR]

Vessel traits contribute to plant water transport from roots to leaves and thereby influence how plants respond to soil water availability, but the sources of variation in fine root anatomical traits remain poorly understood. Here, we explore the variations of fine root vessel traits along topological orders within and across tropical tree species. Anatomical traits were measured along five root topological orders in 80 individual trees of 20 species from a tropical forest in southwestern China. We found large variations for most root anatomical traits across topological orders, and strong co-variations between vessel traits. Within species, theoretical specific xylem hydraulic conductivity (K th) increased with topological order due to increased mean vessel diameter, size heterogeneity, and decreased vessel density. Across species, K th was associated with vessel fraction in low-order roots and correlated with mean vessel diameter and vessel density in high-order roots, suggesting a shift in relative anatomical contributors to K th from the second- to fifth-order roots. We found no clear relationship between K th and stele: root diameter ratios. Our study shows strong variations in root vessel traits across topological orders and species, and highlights shifts in the anatomical underpinnings by varying vessel-related anatomical structures for an optimized water supply. [ABSTRACT FROM AUTHOR]

The Klausmeier–Gray–Scott model of vegetation dynamics consists of a system of two partial differential equations relating plant growth and soil water. It is capable of reproducing the characteristic spatial patterns of vegetation found in plant ecosystems under water limitations. Recently, a discrete delay was incorporated into this model to account for the lag between water infiltration into the soil and the following water uptake by plants. In this work, we consider a more ecologically realistic distributed delay to relate plant growth and soil water availability and analyse the effects of different delay types on the dynamics of both mean-field and spatial Klausmeier–Gray–Scott models. We consider distributed delays based on Gamma kernels and use the so-called linear chain trick to analyse the stability of the uniformly vegetated equilibrium. It is shown that the presence of delays can lead to the loss of stability in the constant equilibrium and to a reduction of the parameter region where steady-state vegetation patterns can arise through symmetry-breaking by diffusion-driven instability. However, these effects depend on the type of delay, and they are absent for distributed delays with weak kernels when vegetation mortality is low. [ABSTRACT FROM AUTHOR]

The uncertainty in soil hydraulic parameters is often not taken into account in process‐based hydrological modeling. Performing runs with 104 stochastic parameter realizations, we evaluated the propagation of uncertainty in the Van Genuchten–Mualem (VGM) parameters into estimates of the threshold values of soil water content used to calculate the total and readily available water, and on the long‐term (30 years) simulations of evaporation, transpiration, bottom flux, and runoff by the SWAP hydrological model. The simulated scenarios included weather data from a location in southeast Brazil and seven soils from the same region cropped with maize, comprising a wide range of texture classes. The results showed that uncertainties in VGM parameters affect the estimates of total and readily available water. Water balance components obtained by a deterministic simulation with average VGM parameters did not always agree with the average or median of stochastic simulations, and stochastic simulations including parameter uncertainties should be preferred. Variations in yearly rainfall characteristics were more important for bottom flux and evaporation, while transpiration and runoff were more strongly influenced by the variations in soil hydraulic properties. Core Ideas: Hydraulic parameter uncertainty and correlations can be used in stochastic simulations with a hydrological model.Parameter uncertainty propagates more strongly into estimates of plant available water than in its threshold water contents.Stochastic averages of simulated water balance components may differ from deterministically obtained values.Bottom flux and evaporation respond to rainfall, while transpiration and runoff depend most on soil properties. [ABSTRACT FROM AUTHOR]

Damask rose is an important essential oil crop. In the present study, plants were subjected to three different water deficit levels (70, 40, and 10% available water content) for two periods (June–October). Plant phenology, growth, essential oil yield, gas exchange features, membrane stability and major antioxidant defense elements were monitored across two years. Soil water deficit was related to quicker completion of the growth cycle (up to 7.4 d), and smaller plants (up to 49.7%). Under these conditions, biomass accumulation was jointly constrained by decreased leaf area, chlorophyll content, CO2 intake, and photosynthetic efficiency (up to 82.8, 56.9, 27.3 and 68.2%, respectively). The decrease in CO2 intake was driven by a reduction in stomatal conductance (up to 41.2%), while the decrease in leaf area was mediated by reductions in both number of leaves, and individual leaf area (up to 54.3, and 64.0%, respectively). Although the reactive oxygen species scavenging system was activated (i.e., proline accumulation, and enhanced activity of three antioxidant enzymes) by water deficit, oxidative stress symptoms were still apparent. These effects were amplified, as soil water deficit became more intense. Notably, the adverse effects of water deficit were generally less pronounced when plants had been exposed to water severity during the preceding year. Therefore, exposure to water deficit elicited plant tolerance to future exposure. This phenotypic response was further dependent on the water deficit level. At more intense soil water deficit across the preceding year, plants were less vulnerable to water deficit during the subsequent one. Therefore, our results reveal a direct link between water deficit severity and plant tolerance to future water stress challenges, providing for the first time evidence for stress memory in damask rose. [ABSTRACT FROM AUTHOR]

Regular watering is a very important activity in plant maintenance because plants need water to carry out photosynthesis and obtain the nutrients necessary to grow and develop properly. An automatic watering tool has been designed that can perform watering commands remotely. This automatic watering instrument is achieved by using a soil moisture sensor to measure the water content or soil moisture and a DHT22 sensor that can detect air temperature and humidity. Soil moisture information is sent via Telegram, using the Telegram bot feature on this automatic plant watering tool, so that the tool can be controlled remotely. This plant monitoring can save time and energy and maintain plant quality more effectively. Plant conditions can also be checked periodically to ensure that the plant's water needs are being properly met. This automatic plant watering solution therefore has the potential to increase productivity and efficiency in case of irregular watering of the plants. [ABSTRACT FROM AUTHOR]

Increasing wildfire frequency in the Mediterranean Basin could affect future plant-soil–water-dynamics. The capacity of soils to retain water is a key parameter affecting plant post-fire regeneration. Yet, few research has looked at how different soil properties related to water retention is affected by increasing wildfire frequency. This study aimed at understanding the relationship between wildfire frequency, soil–water-related properties and the dynamics of surface water in soils. To this, after a 2012-summer wildfire in Portugal, three sets of three replicate maritime pine stands with contrasted wildfire frequency were selected (0 vs. 1 vs. 4 fires since 1975). At each of the nine study sites, three re-sprouter shrubs and neighbouring bare soil were chosen (54 microsites). There, soil cover, soil–water retention curves and surface (0–5 cm) soil–water-related properties (texture, bulk density, organic matter content, soil moisture, soil surface water repellency) were monitored for one year. Furthermore, records of post-fire soil moisture dynamics were analysed continuously using 72 probes installed at 2.5 and 7.5 cm depth. The hillslopes affected by 1 fire showed higher plant recovery than the 4 fires hillslopes. During the dry season, the threshold for water stress was reached 17 days sooner in the 4 fires hillslopes, and also 10 days sooner on bare microsites. Periods of plant water stress were longer and bare soil patches size bigger. The increase in wildfire frequency promoted high soil organic matter contents but less available water content, stressing the importance of soil organic matter quality characterization in water-related properties. [ABSTRACT FROM AUTHOR]

The effect of foliar applications of PectiMorf® was studied in bean plants (Phaseolus vulgaris L.) cultivated under two irrigation variants. For this, 12 concrete containers were planted with the cultivar "Tomeguín 93". The irrigation consisted of applying 100 and 50 % of the ETc (standard evapotranspiration of the crop) and the PectiMorf® foliar applications were 150 mg ha-1 at 20 and 35 days after sowing giving rise to the following four treatments: T1-100 % ETc, considered as control treatment. T2-100 % ETc + P (P = PectiMorf® application at 20 and 35 DAS) T3-50 % ETc + P and T4- 50 % ETc, considered as stress treatment. Seven days after the PectiMorf® applications (28 and 43 DAS) were evaluated, the soil moisture content and different physiological indicators such as growht in dried biomass, leaf water potential (Ψf), actual osmotic potential (Ψs), osmotic potential at maximum turgor (Ψ100s) and stomatal conductance (gs). In addition, the water potential of the soil at the level of the soil-root interfaces (Ψr) and the contribution of dehydration to changes in potential osmotic ΔΨ ss were calculated. The results showed a positive effect of the foliar applications of PectiMorf® in the improvement of plants water status in both irrigation variants. [ABSTRACT FROM AUTHOR]

A dynamic transition in soil hydrologic states through meteorological variability and terrestrial feedback governs soil‐vegetation‐climate (SVC) interactions, constrained by critical soil moisture (SM) thresholds. However, observational and scaling constraints limit critical SM threshold estimation at the remote‐sensing (RS) footprint scale. Using global surface SM (θRS) from NASA's Soil Moisture Active Passive (SMAP) satellite, we characterize the seasonal preferential hydrologic states of θRS and derive three tipping characteristics to estimate the intensity (Mean Tipping Depth, ε‾ $\overline{\boldsymbol{\varepsilon }}$), frequency (Tipping Count, η), and duration (Mean Tipped Time, τ‾ $\overline{\boldsymbol{\tau }\,}$) of the excursion of θRS from wet‐ to dry‐average conditions. The preferential state provides the seasonally dominant hydrological states of θRS, while tipping characteristics capture the ecosystem linkages of the dynamic transition in θRS hydrologic states. Globally, θRS predominantly exhibits a (unimodal) dry‐preferential state, especially over arid/semi‐arid drylands and a unimodal wet‐preferential θRS state in high‐latitude boreal forests and tundra biomes. Prevalence of (bimodal) bistable θRS state overlaps with regions of strong positive SM‐precipitation coupling and monsoonal climate in semi‐arid/subhumid climates. Seasonal preferential hydrologic states co‐vary with the regional variability in plant water stress threshold and land‐atmospheric coupling strength. Tipping characteristics of θRS show sensitivity to intra‐biome variability in SVC coexistence patterns and display high skill in partitioning global ecoregions. While ε‾ $\overline{\boldsymbol{\varepsilon }}$ and η are climate‐controlled, τ‾ $\overline{\boldsymbol{\tau }\,}$ is moderated by soil and vegetation through their influence over θRS drydown during water‐limited evapotranspiration. Preferential states and tipping characteristics find applications in quantifying SVC coexistence patterns, climate model diagnosis, and assessing ecosystem sensitivity to climate change. Key Points: Global surface soil moisture dynamics is categorized into dry‐preferential, wet‐preferential and bistable hydrologic statesTipping characteristics are defined to capture intensity, frequency, and duration of surface soil moisture excursions from wet‐to dry‐average stateSoil moisture tipping characteristics capture soil‐vegetation‐climate coexistence patterns within global biomes [ABSTRACT FROM AUTHOR]

Accurate prediction of irrigation requirements ensures that water is applied only when necessary, reducing wastage and conserving this precious resource. This study provides a probabilistic framework for determining the irrigation requirements of crops, referred to as the Irrigation Factor (IF). IF was calculated based on three indicators - soil moisture (SM), leaf area index (LAI), and evapotranspiration (ET). Irrigation requirement is determined based on a three-step methodology. First, relevant variables for each indicator are identified using a Random Forest regressor, followed by the development of a Long Short-Term Memory (LSTM) model to predict the three indicators. Second, errors in the simulation are calculated for each indicator by comparing the predicted and actual values in the historical time period, which are then used to calculate the error weights (normalized) of the three indicators for each month to also capture the seasonal variations. Third, we calculate the lower and upper limits by adding the error values (5th and 95th percentiles) to a simulated value. Using these values, we determine the mean, minimum, and maximum levels of irrigation requirement based on the levels' threshold values. To determine the final levels of irrigation requirement at a daily time scale, we multiply the calculated levels (mean, minimum, and maximum) for each indicator by their respective weights. The outcome derived from the test case indicated that while certain variables exhibited no demand for water, there was a necessity for irrigation in other cases, and vice versa. This holistic approach to irrigation scheduling helps to ensure that plants receive adequate water while minimizing water wastage and promoting sustainability. It is especially valuable for agricultural operations, where optimizing water usage is essential economically and environmentally. Highlights: Irrigation Factor (IF) was developed – a probabilistic framework to determine the irrigation requirements of crops. IF was computed by combining three key indicators covering the soil moisture deficit, plant water stress, and atmospheric demand. Combining multiple indicator variables arguably enhanced the robustness of the framework by overcoming the shortcomings within individual variables. The probabilistic nature of the IF framework additionally provided crucial information about the mean, minimum, and maximum irrigation requirements, enabling more informed decision-making, particularly in uncertain scenarios. The easy-to-use IF framework also captures seasonal variations in irrigation requirements, aiding more realistic decision-making. [ABSTRACT FROM AUTHOR]

Samples of scrub plants and soil were collected from May to October 2019 in the subalpine scrub zone of the Qilian Mountains. Based on measured oxygen isotope values (δ18O) in plant xylem water and soil water, the multivariate linear mixed model (IsoSource) and the proportional similarity index (PS index) were used to analyze the using proportion for each potential water source and the competition relationship for water use of scrub plants in different growing periods and habitats. The results showed that the soil water content gradually decreased with increasing depth of the soil layer, with the maximum value in the soil layer of 0–10 cm. Most of the scrub plants mainly used soil water in the soil layer of 0–30 cm during the different periods of growing season, but Salix sclerophylla Anderss. and Salix oritrepha Schneid. on the semi-sunny slope habitat mainly used soil water in the soil layer of 40–80 cm during the middle period of growing season (July–August), with the proportion of 59.5% and 52.1%, respectively; and Potentilla fruticosa Linn. and Salix cupularis Rehd. on the semi-shady slope habitat mainly used soil water in the soil layer of 30–60 cm during the early period of growing season (May–June), with the proportion of 61.1% and 49.7%, respectively. The competition relationships of scrub plants for water use varied during different periods of growing season (P < 0.05). On the semi-sunny slope habitat, they were fiercest for Salix cupularis Rehd. and Rhododendron thymifolium Maxim., Potentilla fruticosa Linn., and Salix sclerophylla Anderss. during the early period of growing season; Salix cupularis Rehd. and Rhododendron thymifolium Maxim. during the middle period of growing season, and Salix sclerophylla Anderss. and Salix oritrepha Schneid. during the end period of growing season (September–October). On the semi-shady slope habitat, they were fiercest for Salix oritrepha Schneid. and Caragana jubata (Pall.) Poir. during the early period of growing season; Rhododendron przewalskii Maxim. and Rhododendron thymifolium Maxim. during the middle period of growing season; and Salix cupularis Rehd. and Salix oritrepha Schneid. during the end period of growing season. This study reveals the competitive relationship of scrub plants for water use in the subalpine zone and their response to environmental changes, so as to provide theoretical references for the ecological conservation in the ecologically fragile areas of the Qilian Mountains. [ABSTRACT FROM AUTHOR]

Revealing the water use pattern of plants influenced by coal-mining-caused land subsidence is crucial to understand plant–water interactions and guide ecological restoration. However, available information on herbaceous plants, the dominant species in most arid and semi-arid regions with abundant coal resources, remains inadequate. We investigated the water use patterns of Stipa bungeana Trin. by measuring soil water content, root distribution, and stable isotopes of hydrogen (δ2H) and oxygen (δ18O) of soil water and plant stem water both before and after a rainfall event. The results revealed that prior to rainfall, both areas exhibited a low soil water content with no discernible difference in soil drought. However, the soil waters δ2H and δ18O were found to be more enriched at varying depths within the subsidence area, indicating a heightened level of soil evaporation. Both soil water content and soil water isotopic composition responded sensitively to rainfall, with rainfall primarily replenishing the shallow layer (0–20 cm), thereby reflecting an infiltration mode dominated by piston flow. More water seeped into deeper soil layers in the subsidence area compared to the non-subsidence area, with more preferential flow. Before rainfall, the sources of plant water uptake were consistent both at shallow and deep soil layers, implying that the proportion of water uptake gradually decreased with increasing depth. After rainfall, the sources of plant water uptake differed slightly between the two soil layers. The plants in non-subsidence and subsidence areas dominantly extracted soil water at depths greater than 10 cm and 20 cm, respectively. The root system in the subsidence area was more developed than that in the non-subsidence area. Plant water uptake was primarily influenced by the spatial distribution of roots, as well as the post-rainfall water distribution, regardless of whether they were in the subsidence area or not. Although land subsidence affected soil water transport, the water uptake pattern of Stipa bungeana Trin. was similar before and after rainfall, indicating the adaptive growth of plants through their roots in the subsidence area. The high adaptability of herbs such as Stipa bungeana Trin. makes them a viable option for vegetation restoration in subsidence areas. This study has significant implications for evaluating plant–water relationships in subsidence areas due to coal mining, thereby providing a fundamental basis and valuable reference for ecological restoration and management strategies within such affected regions. [ABSTRACT FROM AUTHOR]

Compared to fluctuating soil water (FW) conditions, stable soil water (SW) can increase plant water use efficiency (WUE) and improve crop growth and aboveground yield. It is unknown, however, how stable and fluctuating soil water affect root vegetables. Here, the effects of SW and FWwere studied on cherry radish in a pot experiment, using negative pressure irrigation and conventional irrigation, respectively. The assessed effects included agronomic parameters, physiological indices, yield, quality and WUE of cherry radish. Results showed that under similarly average soil water contents, compared with FW, SW increased plant photosynthetic rate, stomatal conductance and transpiration rate, decreased leaf proline content by 13.7-73.3% and malondialdehyde content by 12.5-40.0%, and increased soluble sugars content by 6.3-22.1%. Cherry radish had greater biomass accumulation and nutrient uptake in SWthan in FW. Indeed, SWincreased radish output by 34.6-94.1% with no influence on root/shoot ratio or root quality. In conclusion, soil water stability affected directly the water physiological indicators of cherry radish and indirectly its agronomic attributes and nutrient uptake, which in turn influenced the crop biomass and yield, as well as WUE. This study provides a new perspective for improving agronomy of root crops and WUE through managing soil water stability. [ABSTRACT FROM AUTHOR]

Earthworms can stimulate microbial activity and hence greenhouse gas (GHG) emissions from soils. However, the extent of this effect in the presence of plants and soil moisture fluctuations, which are influenced by earthworm burrowing activity, remains uncertain. Here, we report the effects of earthworms (without, anecic, endogeic, both) and plants (with, without) on GHG (CO2, N2O) emissions in a 3-month greenhouse mesocosm experiment simulating a simplified agricultural context. The mesocosms allowed for water drainage at the bottom to account for the earthworm engineering effect on water flow during two drying-wetting cycles. N2O cumulative emissions were 34.6% and 44.8% lower when both earthworm species and only endogeic species were present, respectively, and 19.8% lower in the presence of plants. The presence of the endogeic species alone or in combination with the anecic species slightly reduced CO2 emissions by 5.9% and 11.4%, respectively, and the presence of plants increased emissions by 6%. Earthworms, plants and soil water content interactively affected weekly N2O emissions, an effect controlled by increased soil dryness due to drainage via earthworm burrows and mesocosm evapotranspiration. Soil macroporosity (measured by X-ray tomography) was affected by earthworm species-specific burrowing activity. Both GHG emissions decreased with topsoil macropore volume, presumably due to reduced moisture and microbial activity. N2O emissions decreased with macropore volume in the deepest layer, likely due to the presence of fewer anaerobic microsites. Our results indicate that, under experimental conditions allowing for plant and earthworm engineering effects on soil moisture, earthworms do not increase GHG emissions, and endogeic earthworms may even reduce N2O emissions. [ABSTRACT FROM AUTHOR]

Simulation models are tools commonly used to predict changes in soil carbon stocks. Prior validation is essential, however, for determining the reliability and applicability of model results. In this study, the process-based biogeochemical model MONICA (Model of Nitrogen and Carbon dynamics on Agro-ecosystems) was evaluated with respect to soil organic carbon (SOC), using long-term monitoring data from 46 German agricultural sites. A revision and parameterisation of equations, encompassing crop- and fertiliser-specific C contents and the abiotic factors of soil temperature, soil water and clay content, were undertaken and included in the model. The modified version was also used for a Morris elementary effects screening method, which confirmed the importance of environmental and management factors to the model's performance. The model was then calibrated by means of Bayesian inference, using the Metropolis–Hastings algorithm. The performance of the MONICA model was compared with that of five established carbon turnover models (CCB, CENTURY, C-TOOL, ICBM and RothC). The original MONICA model systematically overestimated SOC decomposition rates and produced on average a ∼17 % greater mean absolute error (MAE) than the other models. The modification and calibration significantly improved its performance, reducing the MAE by ∼30 %. Consequently, MONICA outperformed CENTURY, CCB and C-TOOL, and produced results comparable with ICBM and RothC. Use of the modified model allowed mostly adequate reproduction of site-specific SOC stocks, while the availability of a nitrogen, plant growth and water submodel enhanced its applicability when compared with models that only describe carbon dynamics. [ABSTRACT FROM AUTHOR]

Plants play a key role in the soil-plant-atmosphere-climate hydrological continuum. Plants depend on the water cycle and, in return, several hydrological processes could be impacted via vegetation-induced mechanisms. Changes in plant composition are known to affect this relationship, however, detailed understanding on how plant characteristics, i.e., their traits, are seldom included in observational and modeling studies. Here we examine the effect of plant traits on water cycle processes in the Amazon Basin. We used remotely-sensed estimates of four plant traits, namely Specific Leaf Area (SLA), Leaf Dry Matter Content (LDMC), Leaf Phosphorus Content (LPC), Leaf Nitrogen Content (LNC), and two vegetation indices, the Normalised Difference Vegetation Index (NDVI), and Leaf Area Index (LAI), for 10 years between 2001 and 2010. We examined the relationship between plant traits and six parameters relevant for water cycle processes, namely Evapotranspiration (ET), Potential Evapotranspiration (PET), Vapour Pressure Deficit (VPD), Land Surface Temperature (LST) Day/Night and Soil Moisture (SM). We used multivariate and quantile regressions to analyse how plant traits explain the average and standard deviation in water cycle process parameters. We find that SLA, NDVI, and LAI exert the strongest effects across the whole of Amazon basin and the sub-basins, most important for the regulation of atmospheric water content and of land surface temperature, but little effect on the regulation of soil moisture content. These effects are exacerbated at extreme values of water process parameters, where plant traits exert an even stronger effect at low values of ET and PET and high values of VPD and LST. Leaf gas exchange traits are most important in comparison to the other traits, and these results also highlight that if water cycle process parameters achieve extreme values, plant traits are key to the persistence of hydrological processes fundamental to the resilience of the Amazon. [ABSTRACT FROM AUTHOR]

To better understand the dynamics and functional roles of root pressure, we represent a novel and the first complete analytical model for root pressure, which can be applied to complex roots/shoots. The osmotic volume of a single root is equal to that of the vessel lumen in fine roots and adjacent apoplastic spaces. Water uptake occurs via passive osmosis and active solute uptake (Js*, osmol s−1), resulting in the osmolyte concentration Cr (mol·kg−1 of water) at a fixed osmotic volume. Solute loss occurs via two passive processes: radial diffusion of solute Km (Cr− Csoil) from fine roots to soil, where Km is the diffusional constant and Csoil is the soil–solute concentration, and the mass flow of solute and water into the plant from the fine roots. The proposed model predicts the quadratic function of root pressure (Pr), Pr2+bPr+c=0, where b and c are the functions of plant hydraulic resistance, soil water potential, solute flux and gravitational potential. The model demonstrates the root pressure‐mediated distribution of water through the hydraulic architecture of a 6.8‐m‐tall bamboo shoot. This model provides a theoretical basis to test the functional roles of root pressure in shaping the hydraulic architecture and refilling potential xylem embolisms. Summary statement: An analytical solution for root pressure is derived and illustrated by applying it to the measured hydraulic architecture of a 7‐m bamboo shoot. [ABSTRACT FROM AUTHOR]

The stable hydrogen and oxygen isotope technique is typically used to explore plant water uptake; however, the accuracy of the technique has been challenged by hydrogen isotope offsets between plant xylem water and its potential source water. In this study, the soil hydrogen and oxygen isotope waterline was used to correct the hydrogen isotope offsets for Salix psammophila and Caragana korshinskii , two typical shrub species on the Chinese Loess Plateau. Five different types of isotopic data [(i) δ18O, (ii) δ2H, (iii) combination δ18O with δ2H, (iv) corrected δ2H and (v) combination δ18O with corrected δ2H] were separately used to determine the water-use patterns of the two shrubs. The δ2H offset values of S. psammophila and C. korshinskii did not show significant temporal variation among the sampling months (May, July and September) but showed notable differences between the two shrubs (−0.4 ± 0.5‰ in S. psammophila vs −4.3 ± 0.9‰ in C. korshinskii). The obtained water absorption proportion (WAP) of S. psammophila in the different soil layers (0–20, 20–60 and 60–200 cm) did not differ significantly among the five different input data types. However, compared with the input data types (iii) and (v), the data types (i), (ii) and (iv) overestimated the WAP of C. korshinskii in the 0–20 cm soil layer and underestimated that in the 60–200 cm layer. The data type (iii) overestimated the WAP of C. korshinskii in 0–20 cm soil layer (25.9 ± 0.8%) in July in comparison with the WAP calculated based on data type (v) (19.1 ± 1.1%). The combination of δ18O and corrected δ2H, i.e. data type (v), was identified as the best data type to determine the water use patterns of C. korshinskii due to the strong correlation between the calculated WAP and soil water content and soil sand content. In general, S. psammophila mainly used (57.9–62.1%) shallow soil water (0–60 cm), whereas C. korshinskii mainly absorbed (52.7–63.5%) deep soil water (60–200 cm). We confirm that the hydrogen isotope offsets can cause significant errors in determining plant water uptake of C. korshinskii , and provide valuable insights for accurately quantifying plant water uptake in the presence of hydrogen isotope offsets between xylem and source water. This study is significant for facilitating the application of the stable hydrogen and oxygen isotope technique worldwide, and for revealing the response mechanism of shrub key ecohydrological and physiological processes to the drought environment in similar climate regions. [ABSTRACT FROM AUTHOR]

Climate change presents a challenge for plants to acclimate their water relations under changing environmental conditions, and may increase the risks of hydraulic failure under stress. In this study, maize plants were acclimated to two different CO2 concentrations ([CO2]; 400 ppm and 700 ppm) while under either water stress (WS) or soil salinity (SS) treatments, and their growth and hydraulic traits were examined in detail. Both WS and SS inhibited growth and had significant impacts on hydraulic traits. In particular, the water potential at 50% loss of stem hydraulic conductance (P 50) decreased by 1 MPa in both treatments at 400 ppm. When subjected to elevated [CO2], the plants under both WS and SS showed improved growth by 7–23%. Elevated [CO2] also significantly increased xylem vulnerability (measured as loss of conductivity with decreasing xylem pressure), resulting in smaller hydraulic safety margins. According to the plant desiccation model, the critical desiccation degree (time×vapor pressure deficit) that the plants could tolerate under drought was reduced by 43–64% under elevated [CO2]. In addition, sensitivity analysis showed that P 50 was the most important trait in determining the critical desiccation degree. Thus, our results demonstrated that whilst elevated [CO2] benefited plant growth under WS or SS, it also interfered with hydraulic acclimation, thereby potentially placing the plants at a higher risk of hydraulic failure and increased mortality. [ABSTRACT FROM AUTHOR]

The need for water increases significantly due to the increase in temperatures and the decrease in water resources with climate change. In increasing agricultural production, along with other factors, it is undeniable that the share of irrigation is very large. The general practice in irrigation is to wet the root zone water content until it reaches field capacity after the irrigation time is determined. However, one of the most fundamental issues in planning a correct irrigation management is the determination and monitoring of soil water content. For this reason, in this study, it was aimed to determine the possibilities of determining and monitoring the soil water content of the plant root zone. The research was carried out in a greenhouse at Akdeniz University Faculty of Agriculture Research and Application Farm in Antalya, where greenhouse crop production is intense. In the study, the usability of the Profile Probe PR2 method, which is an indirect measurement method in determining the soil water content, was investigated. In the evaluation of the Profile Probe PR2 method, the gravimetric method, which is a direct measurement method for soil water content, was used as the basic tool. In the research, it was concluded that the soil water content can be determined quickly, practically and easily with the Profile Probe PR2 method. However, if it is preferred to monitor the soil water content with the Profile Probe PR2 method, it is also recommended to perform a detailed gravimetric calibration study for each soil condition. [ABSTRACT FROM AUTHOR]

Climate change will lead to prolonged droughts in various regions of the world, which may significantly affect agricultural production. This is particularly problematic for soils with low water retention capacity, which cannot store sufficient water for crops. In this paper, we investigate how a change in the water‐holding capacity of the soil material, as could be achieved by increasing the soil organic carbon (SOC) amount, affects the components of the soil water balance (evaporation, transpiration, and groundwater recharge). Specifically, we state the hypothesis that an increased water‐holding capacity in a shallow soil layer, as it is achieved through SOC enrichment at the soil surface, will result in more water being stored near the soil surface and lost to unproductive evaporation, thereby reducing the amount of water available to plants and groundwater recharge. The hypothesis was tested by numerical simulations, employing the Hydrus‐1D program package to model the water balance in a soil–plant–atmosphere system for an arable crop in hydrologically contrasting years. The study considered soils with varying textures and different depths of a soil layer with increased SOC content. The soil hydraulic properties (SHP) of the soil material, including the effect of SOC on the SHP, were determined using a recently developed pedotransfer model based on data from over 500 samples. We showed that both the improved water retention by SOC and its vertical distribution affect the soil water balance in a complex manner. In sandy soils, increasing the water‐holding capacity in shallow layers up to 0.1 m led to enhanced evaporation and thus a decrease in water availability for crops. However, deeper incorporated SOC could ameliorate these negative effects. Our findings suggest that not only the amount but also the vertical SOC distribution should be considered if enrichment of SOC shall be applied to mitigate the effect of droughts. Core Ideas: Addition of soil organic carbon (SOC) alters soil material's hydraulic properties.This, in turn, impacts the water balance of soils under agricultural use.The depth at which SOC is incorporated into soils plays a crucial role in the partitioning of evapotranspiration (ET) into evaporation (E) and transpiration (T).Deeper incorporation of SOC results in greater water availability for plants. [ABSTRACT FROM AUTHOR]

Climate change is often associated with increasing vapour pressure deficit (VPD) and changes in soil moisture (SM). While atmospheric and soil drying often co‐occur, their differential effects on plant functioning and productivity remain uncertain. We investigated the divergent effects and underlying mechanisms of soil and atmospheric drought based on continuous, in situ measurements of branch gas exchange with automated chambers in a mature semiarid Aleppo pine forest. We investigated the response of control trees exposed to combined soil‒atmospheric drought (low SM, high VPD) during the rainless Mediterranean summer and that of trees experimentally unconstrained by soil dryness (high SM; using supplementary dry season water supply) but subjected to atmospheric drought (high VPD). During the seasonal dry period, branch conductance (gbr), transpiration rate (E) and net photosynthesis (Anet) decreased in low‐SM trees but greatly increased in high‐SM trees. The response of E and gbr to the massive rise in VPD (to 7 kPa) was negative in low‐SM trees and positive in high‐SM trees. These observations were consistent with predictions based on a simple plant hydraulic model showing the importance of plant water potential in the gbr and E response to VPD. These results demonstrate that avoiding drought on the supply side (SM) and relying on plant hydraulic regulation constrains the effects of atmospheric drought (VPD) as a stressor on canopy gas exchange in mature pine trees under field conditions. Summary statement: Under high evaporative demand conditions, mature Aleppo pine trees demonstrated increased transpiration and photosynthesis in response to supplementary irrigation. Stomatal conductance exhibited hypo‐sensitivity to increasing water demand (high vapour pressure deficit) but was sensitive to a decrease in water supply, expressed as soil water content or plant water potential. Our findings highlight that water supply, rather than water demand, is the primary limiting factor for transpiration in Aleppo pine trees. [ABSTRACT FROM AUTHOR]

Polylepis trees occur throughout the Andean mountain region, and it is the tree genus that grows at the highest elevation worldwide. In the humid Andes where moisture is rarely limiting, Polylepis trees must adapt to extreme environmental conditions, especially rapid fluctuations in temperature, ultraviolet radiation and vapor pressure deficit (VPD). However, Polylepis ' water-use patterns remain largely unknown despite the importance of understanding their response to microclimate variation to determine their capacity to maintain resilience under future environmental change. We conducted a study in a Polylepis reticulata Kunth forest in the Ecuadorian Andes to evaluate its tree water-use dynamics and to identify the main environmental drivers of transpiration. Tree sap flow was monitored simultaneously with soil volumetric water content (VWC) and microclimate during 2 years for trees growing in forest edge and interior locations. We found that sap flow was primarily controlled by VPD and that VWC exerted a secondary role in driving sap flow dynamics. The highest values for sap flow rates were found when VPD > 0.15 kPa and VCW < 0.73 cm3 cm−3, but these threshold conditions only occurred during brief periods of time and were only found in 11% of our measurements. Moreover, these brief windows of more favorable conditions occurred more frequently in forest edge compared with forest interior locations, resulting in edge trees maintaining 46% higher sap flow compared with interior trees. Our results also suggest that P. reticulata has a low stomatal control of transpiration, as the sap flow did not decline with increasing VPD. This research provides valuable information about the potential impacts of projected future increases in VPD due to climate change on P. reticulata water-use dynamics, which include higher sap flow rates leading to greater transpirational water loss due to this species' poor stomatal control. [ABSTRACT FROM AUTHOR]

The forest ecosystem of Beijing is an important barrier that preserves the ecological environment in the capital city of China. Therefore, the study of plant water utilization techniques in Beijing holds considerable importance in establishing a theoretical framework for the rehabilitation, administration, and preservation of forest ecosystem structures and functions. Here, the samples of precipitation, xylem water, and soil water were collected during the months of August and December 2021 from both mountainous and plains areas of Beijing. We measured the hydrogen and oxygen stable isotope values (δ2H and δ18O, respectively) and demonstrated the water use strategies of two typical tree species (Pinus tabuliformis Carr. and Acer truncatum Bunge) using the MixSIAR model. Divergent water use strategies were found in the mountainous and plains areas of Beijing. In the mountainous area, the two tree species exhibited seasonal differences in water use strategies. The xylem water of P. tabuliformis was mainly derived from the surface soil water (0~20 cm). In contrast, the xylem water of A. truncatum mainly originated from the surface soil water during the growing season, and it mainly originated from the deep soil water (60~100 cm) during the nongrowing season. However, in the plains area, the water sources of P. tabuliformis and A. truncatum did not show seasonal differences and originated mainly from the deep soil water. The findings of our study emphasize the notable disparity in water utilization strategies among tree species in the mountainous and plains areas. Consequently, it is imperative to formulate sustainable forestry management approaches that align with the water use efficiency of trees in various locations of Beijing. [ABSTRACT FROM AUTHOR]

Plant water source partitioning suffers from multiple uncertainty sources including tracers, depleted xylem water deuterium, and mixing models, but the uncertainties have rarely been systematically evaluated. Taking apple trees of different ages as example, we combined four tracers of different characteristics (2H, 3H, 17O, and 18O), two xylem water deuterium bias correction methods (soil water excess and stem relative water content), and four mixing models (IsoSource, SIAR, MixSIR, and MixSIAR) to quantify the total uncertainty and the uncertainty of each component. For the total uncertainty, the contributions of the mixing models were the largest (37%), followed by those of tracers (28%) and interaction of tracers and models (27%), while the contributions of other sources were the smallest (8%). In particular, the xylem water deuterium bias correction methods had an uncertainty of 2%, implying its minor role in deviating plant water source partitioning. After evaluating the performance of the three components with four target functions, we recommend tracer combination of 2H18O with MixSIAR as the best framework for water source partitioning of apple trees on the Loess Plateau. The decomposed uncertainties and recommended methods provide technical support and promote understanding of variable results in plant water source partitioning. Plain Language Summary: Plants may absorb water from multiple sources, including precipitation, soil water of different layers, streamwater, and groundwater. Identifying the plant water source is important for management of plant productivity and water resources. In this context, the isotope‐based methods have been widely applied to partition plant water sources. However, uncertainties have been detected from tracers, depleted xylem water deuterium, and mixing models. Despite that the above uncertainty sources have been separately explored by different studies, and the contribution of each uncertainty component to the total uncertainty has rarely been investigated. To explore this knowledge gap, we employ four isotopes, two xylem water deuterium correction methods, and four mixing models to generate the possible isotope‐correction method‐mixing model combinations. We compare the uncertainty of each component in these combinations to determine the steps that should be paid more attention in plant water source partitioning. Further, we recommend the best isotope‐correction method‐mixing model combination for plant water source partitioning. Although the recommended method may be limited to the regions with climate and vegetation similar to this study, this study presents a valuable technical insight into the evaluation and selection of methods for plant water source partitioning. Key Points: We decompose the uncertainties in isotope‐based plant water source partitioning, and analyze dominance of each uncertainty componentMixing models and tracers have dominant but deuterium bias correction has negligible effect on partitioned plant water sourcesWe propose a framework on evaluating and selecting the most suitable methods for plant water source partitioning [ABSTRACT FROM AUTHOR]

Proper irrigation practice consists of applying the optimum amount of water to the soil at the right time. The porous characteristics of the soil determine the capacity of the soil to absorb, infiltrate, and store water. In irrigation, it is not sufficient to only determine the water content of the soil; it is also necessary to determine the availability of water for plants: water potential. In this paper, a comprehensive laboratory evaluation—accuracy and variability—of the world's leading commercial water potential sensors is carried out. No such comprehensive and exhaustive comparative evaluation of these devices has been carried out to date. Ten pairs of representative commercial sensors from four different families were selected according to their principle of operation (tensiometers, capacitive sensors, heat dissipation sensors, and resistance blocks). The accuracy of the readings (0 kPa–200 kPa) was determined in two soils of contrasting textures. The variability in the recordings—repeatability and reproducibility—was carried out in a homogeneous and inert material (sand) in the same suction range. The response in terms of accuracy and value dispersion of the different sensor families was different according to the suction range considered. In the suction range of agronomic interest (0–100 kPa), the heat dissipation sensor and the capacitive sensors were the most accurate. In both families, registrations could be extended up to 150–200 kPa. The scatter in the readings across the different sensors was due to approximately 80% of the repeatability or intrinsic variability in the sensor unit and 20% of the reproducibility. Some sensors would significantly improve their performance with ad hoc calibrations. [ABSTRACT FROM AUTHOR]

The intensity and frequency of droughts are projected to rise in recent years and adversely affect forests. Thus, information on plant water use and acclimation during and after droughts is crucial. This study used the stable isotope and thermal dissipation probes to detect the water‐use adaptation of mixed forests to drought using a precipitation gradient control experiment in the field. The results showed that Platycladus orientalis and Quercus variabilis mainly absorbed stable water from deep soil layers during the drought (32.05% and 28.2%, respectively). The synergetic nocturnal sap flow in both species replenished the water loss, but P. orientalis experienced a greater decline in transpiration acclimation to drought. The transpiration of Q. variabilis remained high since it was mainly induced by radiation. After short‐term exposure to drought, P. orientalis majorly obtained shallow soil water, confirming its sensitivity to shallow water. Contrarily, Q. variabilis mainly absorbed stable water from deep soil layers regardless of the soil water content. Therefore, these findings suggest that Q. variabilis cannot physiologically adjust to extreme drought events, possibly limiting their future distributions and altering the composition of boreal forests. Summary statement: 1)Absorbing deep soil water is the main drought survival mechanism of plants.2)Platycladus orientalis experienced greater declines in transpiration acclimation to drought, but Quercus variabilis cannot physiologically adjust to extreme short‐term drought events. [ABSTRACT FROM AUTHOR]

Despite rapid progress in the burgeoning field of flash drought research, few studies directly compare the differences in characteristics between flash drought (commonly understood as quick, rapid‐onset drought) and drought traditionally defined as slow‐moving (henceforth normal drought), particularly over agricultural regions where drought effects may be economically the most disastrous. In this study, flash and normal drought events are identified using reanalysis of soil moisture in the data‐rich agricultural region of the California Central Valley for investigation of characteristics related to agriculture. In particular, we investigate the relative duration of pixels in drought events, the correlation of drought intensity with vegetation condition, the impact of aridity on vegetation response and drought, and the differences in the different characteristics between rainfed and irrigated agriculture. Overall, we found considerable differences between flash and normal drought, particularly in their spatial distributions and behavior in relation to aridity. Flash droughts even indicate a counterintuitive improvement in vegetation condition in the northern, more humid regions, likely due to the release of growth limiting factors (e.g., below‐optimum temperature and radiation) associated with drought. Results also indicate improvements in vegetation conditions during normal drought for irrigated land over rainfed, highlighting the importance of irrigation as a drought protection strategy in agriculture. Plain Language Summary: Flash droughts are droughts that, in contrast to traditionally understood droughts, develop suddenly and rapidly. This can be particularly dangerous for agriculture, since crops can be affected by sudden changes in plant available water. This study identifies differences in drought characteristics over the Central Valley agricultural region of California, such as length of time in drought and effects on vegetation, with considerations for local climate and irrigation. Overall, flash drought shows clear spatial trends that vary with local climate, with some regions showing a benefit to plant health during flash droughts, and irrigated regions performing slightly better. This highlights the importance of irrigation as an adaptation strategy against drought. Key Points: Flash droughts exhibit significantly different spatial distributions and trends in characteristics than normal droughtsAridity can provide useful clues about vegetation condition and irrigation's effectiveness during droughtFlash drought conditions (temperature and radiation) may alleviate plant growth limitations in cooler climates, improving vegetation condition [ABSTRACT FROM AUTHOR]

In arid and semi-arid areas, plant growth and survival are directly related to the soil water content. The soil water content is an important parameter for monitoring land degradation. A better understanding of how forests use soil water is crucial for the quantification how the terrestrial hydrologic cycle adapts to forestry practices and regional climate anomalies in these areas. This study investigated the variation of the water balance under different precipitation patterns (including soil water redistribution patterns under water stress and extreme rainstorms) under three common tree species in a mountainous area of Beijing were investigated. The results showed that soil water storage in the 80–150 cm layer played an important role for the ability of Platycladus orientalis (L.) Franco and Quercus variabilis Blume to survive drought during a dry season. Compared to P. orientalis and Q. variabilis, the duration of water stress was shortest for Pinus tabulaeformis Carr. (15 months). P. tabulaeformis had a higher ability to utilize top soil water but showed a less balanced use of soil water in each soil layer. It also had the strongest ability to replenish groundwater through deep seepage. P. tabulaeformis may resist drought by transferring water to deeper soil horizons, where it is less susceptible to evaporation and where moisture can be temporarily stored. P. orientalis and Q. variabilis are more dependent on soil water storage in response to water stress conditions. [ABSTRACT FROM AUTHOR]

As global mean temperature rises, extreme drought events are expected to increasingly affect regions of the United States that are crucial for agriculture, forestry, and natural ecology. A pressing need is to understand and anticipate the conditions under which extreme drought causes catastrophic failure to vegetation in these areas. To better predict drought impacts on ecosystems, we first must understand how specific drivers, namely, atmospheric aridity and soil water stress, affect land surface processes during the evolution of flash drought events. In this study, we evaluated when vapor pressure deficit (VPD) and soil moisture thresholds corresponding to photosynthetic shutdown were crossed during flash drought events across different climate zones and land surface characteristics in the United States. First, the Dynamic Canopy Biophysical Properties (DCBP) model was used to estimate the thresholds that define reduced photosynthesis by assimilating vegetation phenology data from theModerate Resolution Imaging Spectroradiometer (MODIS) to a predictive phenology model. Next, we characterized and quantified flash drought onset, intensity, and duration using the standardized evaporative stress ratio (SESR) and NLDAS-2 reanalysis. Once periods of flash drought were identified, we investigated how VPD and soil moisture coevolved across regions and plant functional types. Results demonstrate that croplands and grasslands tend to be more sensitive to soil water limitations than trees across different regions of the United States. We found that whether VPD or soil moisture was the primary driver of plant water stress during drought was largely region specific. The results of this work will help to inform land managers of early warning signals relevant for specific ecosystems under threat of flash drought events. [ABSTRACT FROM AUTHOR]

Soil moisture is a key variable in monitoring climate and an important component of the hydrological, carbon, and energy cycles. Satellite products ameliorate the sparsity of field measurements but are inherently limited to observing the near-surface layer, while water available in the unobserved root-zone controls critical processes like plant water uptake and evapotranspiration. A variety of approaches exist for modelling root-zone soil moisture (RZSM), including approximating it from surface layer observations. While the number of available RZSM datasets is growing, they usually do not contain estimates of their uncertainty. In this paper we derive a long-term RZSM dataset (2002–2020) from the Copernicus Climate Change Service (C3S) surface soil moisture (SSM) COMBINED product via the exponential filter (EF) method. We identify the optimal value of the method's model parameter T , which controls the level of smoothing and delaying applied to the surface observations, by maximizing the correlation of RZSM estimates with field measurements from the International Soil Moisture Network (ISMN). Optimized T -parameter values were calculated for four soil depth layers (0–10, 10–40, 40–100, and 100–200 cm) and used to calculate a global RZSM dataset. The quality of this dataset is then globally evaluated against RZSM estimates of the ERA5-Land reanalysis. Results of the product comparison show satisfactory skill in all four layers, with the median Pearson correlation ranging from 0.54 in the topmost to 0.28 in the deepest soil layer. Temporally dynamic product uncertainties for each of the RZSM product layers are estimated by applying standard uncertainty propagation to SSM input data and by estimating structural uncertainties in the EF method from ISMN ground reference measurements taken at the surface and at varying depths. Uncertainty estimates were found to exhibit both realistic absolute magnitudes and temporal variations. The product described here is, to the best of our knowledge, the first global, long-term, uncertainty-characterized, and purely observation-based product for RZSM estimates up to 2 m depth. [ABSTRACT FROM AUTHOR]

The paper presents the course of variability of the moisture content of the top layers in shallow (45 cm) and medium-deep (90 cm) peat-moorsh soil profiles in the years 2015-2019 against the background of the same meteorological conditions and a similar level of the groundwater table. The relative precipitation index (RPI) classifies the years 2015 and 2016 as dry, 2017 as wet, and 2018 and 2019 as average. For periods of atmospheric droughts, the average daily climatic water balance (CWB) ranged from -5.30 to -1.35 mm·d-1. The water table did not fall below 90 cm b.g.l. during the entire study period, and the range of its fluctuations was 8 cm greater in the shallow than in the medium-deep profile. The range of moisture at different depths varied significantly and ranged from approx. 6% in periods of drought to about 80% in wet periods. Soil moisture throughout the measurement period was above the plant available water range (pF > 4.2). The occurrence of soil drought in the shallow peat-moorsh soil profile had a range of up to 40 cm, and in the medium-deep profile of up to 30 cm. The sequence of no-precipitation days and the maximum amount of daily evapotranspiration during them determine the possible timing of drought; however, it is the precipitation distribution in individual months, considered in the current CWB values, that ultimately determine the formation of soil water resources at the research site. [ABSTRACT FROM AUTHOR]

Application of biochar amendments in agricultural systems has received much attention in recent years. In this study, we assess the 5‐year impacts of biochar application on soil water and plant interactions for an irrigated fresh market tomato (Solanum lycopersicum) and a rainfed pasture (Poaceae) cropping system. In particular, we focus on three varieties of locally produced biochar from agricultural waste materials—almond shell, walnut shell, and almond pruning residues that are pyrolyzed using a mobile pyrolysis unit. We used the soil hydrological model HYDRUS‐1D to explicitly track seasonal and annual soil water fluxes through changes in water retention, drainage, evaporation, and plant water uptake under biochar application. Modeling results show that the application of biochar at 5% increased soil water availability within the top 20 cm for a rainfed system, irrespective of biochar amendment type. This is clearly indicative of higher plant water uptake and greater water use efficiency (WUE) under biochar application. In contrast, a similar biochar amendment for the irrigated system did not affect WUE, instead reducing seasonal soil evaporation loss and thereby reducing irrigation demand. In both cropping systems, year‐to‐year variability in precipitation significantly impacted the total amount of water saved under biochar application with certain amendments retaining more water than others. Given that biochar application increased water retention irrespective of cropping systems, we further used a simple approach to determine yield trade‐off, if any, between control and biochar treatments. Our economic balance clearly demonstrates that the water saved by amending soil with biochar does not offset the yield disparity if compensated with carbon credits and therefore, application of biochar should be actively considered for both its direct and indirect benefits to potential greenhouse gas mitigation (e.g., diverting orchard waste from open burning), water savings, and soil health. Core Ideas: A soil hydrological model was used to evaluate the midterm (5‐year) effects of three biochar types, derived from local agriculture waste using a mobile pyrolyzer, on soil water and plant uptake dynamics.Two common cropping systems with different irrigation schemes were assessed using the model.Biochar application reduced total predicted soil evaporation in both systems.More agronomic benefits are observed in the rainfed system as compared to the irrigated system.Indirect benefits linked to biochar application (e.g., carbon credit) must be considered for economic feasibility. [ABSTRACT FROM AUTHOR]

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