Water Stress History Research Articles

Models for Considering the Thermo-Hydro-Mechanical-Chemo Effects on Soil–Water Characteristic Curves

The soil–water characteristic curve (SWCC) is widely used as a tool in geotechnical, geo-environmental, hydrology, and soil science fields for predicting and interpreting hydro-mechanical behaviors of unsaturated soils. Several previous studies focused on investigating the influence of initial water content, stress history, temperature, and salt content on the SWCC behavior. However, there is still limited understanding to be gained from the literature on how we can systematically incorporate the influence of complex thermo-hydro-mechanical-chemo (THMC) effects into interpreting and predicting the behavior of unsaturated soils. To address that knowledge gap, in this study, the coupled influence of temperature, initial stress state, initial density, soil structure, and chemical solution effects was modeled using established SWCC equations from the literature. The methodology for incorporating the coupled effects of these influential factors is presented herein. Furthermore, we evaluated the SWCC models proposed in this study, enabling us to provide a comprehensive discussion of their strengths and limitations, using the published SWCC data from the literature. The developments outlined in this paper contribute toward facilitating a rigorous approach for analyzing the THMC behaviors of unsaturated soils.

Intermittent water stress favors microbial traits that better help wheat under drought.

Microorganisms can improve plant resistance to drought through various mechanisms, such as the production of plant hormones, osmolytes, antioxidants, and exopolysaccharides. It is, however, unclear how previous exposure to water stress affects the functional capacity of the soil microbial community to help plants resist drought. We compared two soils that had either a continuous or intermittent water stress history (WSH) for almost 40 years. We grew wheat in these soils and subjected it to water stress, after which we collected the rhizosphere soil and shotgun sequenced its metagenome. Wheat growing in soil with an intermittent WSH maintained a higher biomass when subjected to water stress. Genes related to indole-acetic acid and osmolyte production were more abundant in the metagenome of the soil with an intermittent WSH as compared to the soil with a continuous WSH. We suggest that an intermittent WSH selects traits beneficial for life under water stress.

The response of wheat and its microbiome to contemporary and historical water stress in a field experiment

In a field experiment, we evaluated the impact of 37 years of contrasting water stress history on the microbial response in various plant compartments at two distinct developmental stages when four wheat genotypes were exposed to contemporary water stress. Seeds were collected and sampled at the end of the experiment to characterize endophytic and epiphytic microbial communities. Amplicon sequencing data revealed that plant development stage and water stress history were the main factors shaping the microbiome of the major plant parts in response to contemporary water limitation. Our results indicate that seeds can become colonized by divergent microbial communities within a single generation based on the initial pool of microbes as determined by historical contingencies, which was modulated by the contemporary environmental conditions and the plant genotype. Such information is essential to incorporate microbial-based strategies into conventional plant breeding to enhance plant resistance to stress.

Relative and Quantitative Rhizosphere Microbiome Profiling Results in Distinct Abundance Patterns.

Next-generation sequencing is one of the most popular and cost-effective ways of characterizing microbiome in multiple samples. However, most of the currently available amplicon sequencing approaches are limited, as they result in relative abundance profiles of microbial taxa, which does not represent actual abundance in the environment. Here, we combined amplicon sequencing (16S rRNA gene for bacteria and ITS region for fungi) with real-time quantitative PCR (qPCR) to characterize the rhizosphere microbiome of wheat. We show that changes in the relative abundance of major microbial phyla do not necessarily follow the same pattern as the estimated quantitative abundance. Most of the bacterial phyla linked with the rhizosphere of plants grown in soil with no history of water stress showed enrichment patterns in their estimated absolute abundance, which was in contradiction with the trends observed in the relative abundance data. However, in the case of the fungal groups (except for Basidiomycota), such an enrichment pattern was not observed and the abundance of fungi remained relatively unchanged under different soil water stress history when estimated absolute abundance was considered. Comparing relative and estimated absolute abundances of dominant bacterial and fungal phyla, as well as their correlation with the functional processes in the rhizosphere, our results suggest that the estimated absolute abundance approach gives a different and more realistic perspective than the relative abundance approach. Such a quantification approach provides complementary information that helps to better understand the rhizosphere microbiomes and their associated ecological functional processes.

Four decades of soil water stress history together with host genotype constrain the response of the wheat microbiome to soil moisture.

There is little understanding about how soil water stress history and host genotype influence the response of wheat-associated microbiome under short-term decreases in soil moisture. To address this, we investigated how plant breeding history (four wheat genotypes; two with recognized drought resistance and two without) and soil water stress history (same wheat field soil from Saskatchewan with contrasting long-term irrigation) independently or interactively influenced the response of the rhizosphere, root and leaf bacterial and fungal microbiota to short-term decreases in soil water content (SWC). We used amplicon sequencing (16S rRNA gene for bacteria and ITS region for fungi) to characterize the wheat microbiome. Fungal and bacterial communities responses to short-term decreases in SWC were mainly constrained by soil water stress history, with some smaller, but significant influence of plant genotype. One exception was the leaf-associated fungal communities, for which the largest constraint was genotype, resulting in a clear differentiation of the communities based on the genotype's sensitivity to water stress. Our results clearly indicate that soil legacy does not only affect the response to water stress of the microbes inhabiting the soil, but also of the microorganisms more closely associated with the plant tissues, and even of the plant itself.

A water stress-adapted inoculum affects rhizosphere fungi, but not bacteria nor wheat.

Here, we tested if inoculating microbial communities adapted to water stress would increase wheat resistance to water stress. Wheat plants were grown for 4 weeks in high and low diversity soils under well-watered conditions, after which they were subjected to a water stress. After another 2 weeks, the rhizospheres were inoculated with microbial communities extracted from soils with or without a history of water stress. The inoculations did not have significant effects on the plant growth, water content and catalase activity, and on the bacterial communities. However, the inoculation did successfully, though modestly, modify the fungal community, shifting the rhizosphere communities toward the inoculated communities. As hypothesized, these shifts were more pronounced and significant in the low diversity soil, and for the inoculum with a water stress history. Whereas the effects of inoculation were relatively subtle, the water stress resulted in large differences in the wheat phenotype and in both the bacterial and fungal communities. Generally, the microbial changes that followed the water stress were in large part due to shifts in the relative abundance of OTUs that were already present before the stress, rather than to the recruitment of microorganisms from the inoculum or the bulk soil.

Water stress history and wheat genotype modulate rhizosphere microbial response to drought

Different crop genotypes and soils with different water stress histories are known to harbour different microorganisms, but their relative effect on the response of plant-associated microbes to water stress is not known. In a pot experiment, four wheat genotypes (two with recognized drought resistance and two without) were grown in semi-arid soils with different irrigation histories (irrigated and non-irrigated soils) and exposed to four levels of soil water content (ranging from high to low). After one month of exposure to different soil water contents, we examined plant biomass as well as a general (CO2 production) and a specialized (soil uptake of atmospheric H2) functional processes in the rhizosphere. We further measured the abundance of bacteria and fungi in the rhizosphere using real-time PCR. Wheat shoot biomass was lower when growing in non-irrigated soils under low water content. In contrast, under moderate water contents wheat grown in non-irrigated soils had a significantly higher root biomass compared with those grown in irrigated soils. CO2 production did not differ between genotypes and soil irrigation histories under low soil water content. However, we found significantly higher H2 oxidation rates under low water content in the rhizosphere of plants growing in formerly irrigated soil as compared to those grown in formerly non-irrigated soils, although the intensity of the change was genotype-specific. Bacterial abundance was more sensitive to decreasing soil water content than fungal abundance and was mainly influenced by soil water stress history. Taken together, our results highlight that wheat breeding history and soil water stress history differentially influence crop growth performance, a specialized and a general rhizosphere processes, and rhizosphere bacterial and fungal abundance in the face of decreasing soil water content.

Accounting for evolving pore size distribution in water retention models for compacted clays

SummaryWater retention in compacted clays is dominated by multi‐modal pore size distribution which evolves during hydro‐mechanical paths depending on water content and stress history. A description of the evolutionary fabric has been recently introduced in models for water retention, but mostly on a heuristic base. Here, a possible systematic approach to account for evolving pore size distribution is presented, and its implications in models for water retention are discussed. The approach relies on quantitative information derived from mercury intrusion porosimetry data. The information is exploited to introduce physically based evolution laws for the parameters of water retention models. These laws allow tracking simultaneously the evolution of the aggregated fabric and the consequent hydraulic state of compacted clays. The influence of clay microstructure, mechanical constraints and water content changes on the water retention properties is highlighted and quantified from experimental data on different compacted soils with different activity of the clayey fraction. The framework is discussed with reference to a widespread water retention model and validated against experimental data on a Sicilian scaly clay compacted to different dry densities and subjected to a number of hydro‐mechanical paths. Copyright © 2014 John Wiley & Sons, Ltd.

A water stress index based on water balance modelling for discrimination of grapevine quality and yield

<p style="text-align: justify;"><strong>Aims</strong>: A water stress index based on a water balance model was tested as a tool for classifying the water stress paths experienced by grapevines in various French Mediterranean vineyards. The relations between the index value and grapevine yield and berry quality (sugars, organic acids, anthocyanins) at harvest were investigated.</p><p style="text-align: justify;"><strong>Methods and results</strong>: A data set of 102 situations, each combining one location, one variety, one vintage and one water regime (irrigation or, most often, no irrigation), was collected for the study. The Fraction of Transpirable Soil Water (FTSW) was simulated by a unique-soil-reservoir water balance model at a daily time step. Five classes of water deficit were delimited from specific decreasing thresholds of FTSW over four periods between flowering and harvest. These thresholds were derived from predawn leaf water potential values because over decades, grapegrowers and researchers have shared references and built expertise by using this variable throughout the Mediterranean region. A water stress index resulting from the levels of water deficit reached at each of the four periods of the cycle was calculated. This index was correlated with yield per vine, berry weight, and berry sugar and organic acid contents but not with berry anthocyanin content.</p><p style="text-align: justify;"><strong>Conclusion</strong>: A simple water stress index, based on the water balance model, exhibited significant correlations with yield and berry quality for various cultivars and pedo-climatic conditions in Mediterranean vineyards.</p><p style="text-align: justify;"><strong>Significance and impact of the study</strong>: This water stress index is a valuable tool for explaining the variations in grape yield and quality among various locations and years because it reflects the vineyard water stress history in relation to rainfall regime and soil conditions. Improvement would come from the simulation of FTSW during winter, notably for soils of high Total Transpirable Soil Water. One potential application is the quantification of water stress change brought by irrigation in Mediterranean vineyards, and its relation to grapevine production.</p>

Combined effect of irrigation regime and fruit load on the patterns of trunk-diameter variation of ‘Hass’ avocado at different phenological periods

The objective was to investigate the combined effect of irrigation regime and fruit load on trunk-diameter variation patterns of ‘Hass’ avocado trees grown in lysimeters, at different phenological periods. Plant water uptake of both fruited and defruited trees was monitored at high temporal resolution during successive growth stages. The trunk growth rate (TGR) during all the experiments was not affected by the irrigation treatments, yet daily TGR fluctuated significantly during the season, probably in association with periodic changes in the priority of partitioning of carbohydrates between reproductive and vegetative plant organs, i.e., flushes of shoot or root growth. Fruit load clearly played a dominant role in determining TGR, very likely because of the dramatic effect of fruit load on stomatal conductance and leaf carbohydrate concentration and, therefore, on the overall availability of assimilates. Thus, analyses of trunk diameter variation (TDV) data that lead to evaluation of TGR and maximum trunk diameter variation (MTDV) reflect phenological stages and periodicity of shoot, fruit and root growth, and also may provide an integrative, “holistic viewpoint” of overall tree status.The observed high dependency between the MTDV and irrigation treatments may indicate that MTDV actually depends on water-stress history rather than on the actual plant-water status. Thus, MTDV cannot be used on an absolute basis for irrigation management control. On the other hand, it may be a very efficient aid to control irrigation when used on a relative basis, after identifying the impacts of local phenological and environmental factors on the MTDV. Furthermore, the immediate MTDV response to accidental faults may illustrate the advantages of using dendrometer devices for remotely controlling irrigation systems.

Physiological Responses of Gold Kiwifruit (Actinidia chinensis) to Reduced Irrigation

Information on water relations and water stress physiology of Actinidia chinensis Planch. is scant. We aimed at providing such information by exposing potted 1-year-old plants to reduced irrigation in a glasshouse. The treatments were control (C) receiving sufficient water to replace 100% of evapotranspiration, early (E) reduced irrigation for 13 days earlier in the experiment, late (L) reduced irrigation for 13 days later in the experiment, and recovery (R) undergoing E and L with 5 days of full irrigation in between to recover from E. All plants were fully watered between early and late episodes of reduced irrigation. Soil volumetric water content was lower in E, L, and R compared with C, leading to lower leaf water potential, photosynthetic rate (Pn), and stomatal conductance (gs). Pn was lower in the reduced irrigation vines only when gs was below 0.1 mol·m−2·s−1. High leaf temperature in the glasshouse imposed nonstomatal limitations to photosynthesis as indicated by elevated internal leaf CO2 concentrations (Ci). Following rewatering, the stressed vines showed rapid recovery of leaf water potential and photosynthesis. However, Ci and gs were slower to respond. There was an indication of osmotic adjustment in leaves under reduced irrigation. Discrimination against 13CO2 was the same among the treatments. A. chinensis had better stomatal control under water stress compared with Actinidia deliciosa, for which some information is available. Water stress history in A. chinensis encouraged more drought resistance in the subsequent water stress period, but this was not sustained. Although field performance of A. chinensis under water stress is expected to be better than what we have presented here, long periods of deficit irrigation for this species cannot be recommended.

INFLUENCE OF WATER STRESS CONDITIONING ON PHOTOSYNTHETIC WATER STRESS RESPONSE OF SWITCHGRASS (PANICUM VIRGATUM L.) AND TALL FESCUE (FESTUCA ARUNDINACEA SCHREB.)

The objective of this study was to investigate the influence of water stress conditioning on the photosynthesis response of switchgrass (Panicum virgatum L.) and tall fescue (Festuca arundinacea Schreb.) to moisture deficiency. Tillers of the two species were grown in the same, controlled, environment and were subjected to three conditioning water stress cycles, or were kept well watered. After drought conditioning all plants were subjected to moisture deficiency while photosynthesis and leaf water potential were monitored. Measurements were taken between –0.8 and –4.0 MPa and the rate of water stress was 0.49 MPa/day. The conditioning of switchgrass produced a 26% reduction in the photosynthesis rate during drought, while that of tall fescue produced a 57% reduction in photosynthesis. Both species maintained elongation and photosynthesis down to lower leaf water potentials after drought conditioning than before conditioning. The conditioning water stress cycles decreased the leaf conductance, mesophyll resistance and transpiration of tall fescue plants after rewatering. The leaf water potential of conditioned switchgrass plants was lower upon rewatering after three conditioning water stress cycles than the leaf water potential of non-conditioned plants, while the leaf conductance, mesophyll resistance and transpiration of conditioned and non-conditioned tillers were equal. These data indicate an improvement in the drought tolerance of tall fescue and switchgrass plants, emphasize the importance of knowing the previous water stress history of the plants in moisture deficiency experiments, and help to choose proper irrigation management for switchgrass and tall fescue.

Chemical kinetic model of interfacial degradation of adhesive joints

Mechanical properties of adhesive joints are degraded in the presence of water. The progressive decrease in strength has been attributed to propagation of interfacial crack. Water diffusion and stress distribution within the adhesive joint as a function of time has been modeled using finite elements in this study. The stress history at the interface displayed spatially invariant characteristics similar to that of interfacial water concentration variation as a function of diffusion. The water-stress history along the interface can be modeled as a function dependent principally on water concentration without dependence on position. On this basis, a chemical kinetic model is proposed to explain the joint strength degradation data reported in literature.

The influence of soil structure and stress history on the soil–water characteristics of a compacted till

The soil–water characteristic defines the relationship between the soil suction and gravimetric water content, w, or the volumetric water content, θ, or the degree of saturation, S. Theoretical and empirical relationships are available to model the unsaturated soil properties such as the coefficient of permeability and shear strength using the soil–water characteristic and the conventional saturated soil properties. These procedures are attractive to engineering practitioners because rigorous laboratory tests on unsaturated soil are difficult and time-consuming and, therefore, costly. Various investigators generally have used the soil–water characteristic over a limited suction range (usually 0 to about 1500 kPa) to model the unsaturated soil behaviour. Soils, however, change from a saturated to a dry condition over a range of suctions from 0 to 1000 000 kPa. A rationale for extending the soil–water characteristic up to 1000 000 kPa is provided in this paper, and a method for estimating the residual state of saturation is presented. Soil–water characteristics were developed for the entire range of suctions from 0 to 1000 000 kPa on statically compacted clayey till specimens prepared at three different initial water contents. The influence of initial water content, soil structure and stress history, as it relates to the soil–water characteristic, has been studied and is reported in this paper. The initial water contents selected for this study represent the dry of optimum, optimum and wet of optimum conditions with corresponding densities determined from the standard AASHTO test. The results indicate that initial moulding water content has considerable influence on the resulting structure (and aggregation), which in turn influences the soil–water characteristics. In the low suction range (i.e. 0–1500 kPa), macrostructure governs the soil–water characteristics for specimens compacted with dry of optimum initial water contents and they exhibit a steeper slope. However, for the specimens compacted at wet of optimum, microstructure governs the soil–water characteristic behaviour. The soil–water characteristic of the specimens compacted at dry of optimum are influenced by the stress history; however, stress history appears to have no significant influence on the soil–water characteristics of the specimens compacted with wet of optimum conditions. The soil–water characteristic behaviour of specimens compacted with optimum initial water contents lies in between those of specimens compacted with water contents that are dry and wet of optimum. It appears that soil–water characteristics are not significantly influenced either by the soil structure (aggregation) or the stress history for the high suction ranges (i.e. 20 000–1 000 000 kPa).

The relations between leaf water potential of cotton plants and environmental and plant factors

An equation for calculating leaf water potential ( Ψ 1) of cotton ( Gossypium hirsutum L.) plants, based on environmental and plant factors, was developed. Two irrigation experiments were conducted with cotton (cv. Acala SJ-2), on a loamy clay soil. Data from 18 treatments of one experiment were pooled and used for multiple regression analysis with Ψ 1 as the dependent variable. The parameter displaying the highest correlation with Ψ 1 was the reciprocal of the relative soil water content in the upper 105 cm of the soil profile. A regression equation combining this factor with air temperature, an index indicating the crop's water stress history and plant height explained 87% of the variation in Ψ 1. The Ψ 1 calculated by using this equation showed good correspondence ( r = 0.9) with data from eight distinct irrigation treatments of the other experiment. It was shown that Ψ 1 of cotton plants can be reliably calculated based on some readily available variables.

Soil Strength Indices as Indicators of Consolidation

ABSTRACT SHEAR strength indices are often used to estimate soil characteristics related to erosion. The purpose of this study was to evaluate the effectiveness of using soil strength indices as indicators of soil changes caused by consolidation. Fall-cone, torvane shear, and pocket penetrometer measurements were obtained on clay, silt loam, and fme sand soils as a function of soil water stress history and time. Also, wet aggregate stability was measured for the clay soil. Prestress suction was the dominant mechanism for strengthening the three soils. Time effects were less pronounced. The fall-cone was the best indicator of consolidation and the pocket penetrometer was also effective with some limitations. The torvane shear device was the least effective index for detecting strength changes, although it worked well on the silt loam soil. The three index tests did not rank the three soils the same in order of increasing strength, suggesting that the validity of using index tests to rank or compare soils is questionable. The results of the study indicated that proper strength index tests may be effective in characterizing relative changes in stability of a given soil over time.

Water stress preconditioning and cotton root pressure-flux relationships

Because little is known about the effects of water stress preconditioning on the pressure-flux relationships of cotton roots, we investigated some of these relationships using detopped root systems of potted cotton (Gossypium hirsutum L.) plants. Water stress preconditioning decreased root pressure flux by 51% compared to the well-watered control. Preconditioning had no effect on the exponential nature of the increasing pressure-flux relationship, but did displace the curve such that the flux was lessened at all increasing and decreasing pressures applied. We suggest that the exponential flux response to increasing pressure was by infiltration of intercellular air spaces in the root cortex at higher pressures. With inverted water potential gradients, preconditioning resulted in significantly less water flowing from the roots to the soil. These effects of previous water stress history on the various flux relationships might be associated with an increased root resistance following the stress, and it is suggested that the controlling mechanism is located in the endodermis.

The effect of stress history and container ventilation on avocado fruit polyphenol oxidase activity

SummaryMature cv Fuerte avocado fruits were picked from trees with and without a water stress history during early fruit development. The interaction between stress and restricted container ventilation, after storage at 5.5°C for 30 days, in relation to the fruit browning potential of soft fruit as evidenced by polyphenol oxidase (PPO) activity was investigated. Soluble PPO activity increased in fruit from stressed (infrequently irrigated) trees when ripened after being placed for 48 h in restricted ventilation. Fruit from moderately irrigated (non-stressed) trees showed no increase. Total PPO showed a similar but not significant trend. It is concluded that restricted ventilation causes a release of bound PPO. It is speculated that stress history predisposes fruit to membrane breakdown under restricted ventilation conditions, resulting in a higher browning potential for such fruit.

Growth and Water Use of Tall Fescue as Influenced by Several Soil Drying Cycles1

AbstractMany investigations have studied various physiological processes using plants watered on a schedule with the effect of this watering schedule seldom considered significant. An understanding of the effect of watering frequency on growth and water use is required to understand water stress tolerance of tall fescue (Festuca arundinacea Schreb.). Experiments were designed to evaluate the effect of watering schedule in greenhouse grown tall fescue on growth, water use, and meristem tissue water status. Growth and water use as well as water, osmotic, and turgor potential of the leaf meristematic region were measured on tall fescue seedlings that had been exposed to several Maury soil (a fine, mixed, mesic Typic Paleudalfs) drying cycles (stressed and daily watered). Growth, measured as leaf extension rate (LER), was greater for seedlings watered to field capacity every 4th day than daily watered seedlings when soil of both treatments was allowed to dry. No significant difference in water potential or osmotic potential was observed during the experiment, and the differential LER was not dependent on turgor potential of the meristematic area which was similar to both treatments. Water use was 50 to 100% higher in control seedlings during the first 48 h of a soil drying cycle than in stressed seedlings. After several soil drying cycles the enhanced growth of stressed plants increased as high as 280%, then declined over the next 24 days of daily watering to about 50% above the control. The enhanced LER did not result in greater shoot fresh weights, but, repeated soil drying depressed root development. Consequently, growth, water status, and water use by tall fescue plants during an experiment must be evaluated in terms of the plants prior water stress history.

Paraheliotropic leaf movement in Siratro as a protective mechanism against drought-induced damage to primary photosynthetic reactions: damage by excessive light and heat

Damage to primary photosynthetic reactions by drought, excess light and heat in leaves of Macroptilium atropurpureum Dc. cv. Siratro was assessed by measurements of chlorophyll fluorescence emission kinetics at 77 K (-196°C). Paraheliotropic leaf movement protected waterstressed Siratro leaves from damage by excess light (photoinhibition), by heat, and by the interactive effects of excess light and high leaf temperatures. When the leaves were restrained to a horizontal position, photoinhibition occurred and the degree of photoinhibitory damage increased with the time of exposure to high levels of solar radiation. Severe inhibition was followed by leaf death, but leaves gradually recovered from moderate damage. This drought-induced photoinhibitory damage seemed more closely related to low leaf water potential than to low leaf conductance. Exposure to leaf temperatures above 42°C caused damage to the photosynthetic system even in the dark and leaves died at 48°C. Between 42 and 48°C the degree of heat damage increased with the time of exposure, but recovery from moderate heat damage occurred over several days. The threshold temperature for direct heat damage increased with the growth temperature regime, but was unaffected by water-stress history or by current leaf water status. No direct heat damage occurred below 42°C, but in water-stressed plants photoinhibition increased with increasing leaf temperature in the range 31-42°C and with increasing photon flux density up to full sunglight values. Thus, water stress evidently predisposes the photosynthetic system to photoinhibition and high leaf temperature exacerbates this photoinhibitory damage. It seems probable that, under the climatic conditions where Siratro occurs in nature, but in the absence of paraheliotropic leaf movement, photoinhibitory damage would occur more frequently during drought than would direct heat damage.