Previous Water Stress Research Articles

Does Pre-Acclimation Enhance the Tolerance of Quercus ilex and Arbutus unedo Seedlings to Drought?

Mediterranean forests are severely threatened by increasing seedling mortality due to harsh environmental conditions, especially drought. In this study, we investigate whether seedlings of Quercus ilex and Arbutus unedo, previously exposed to water deficit, acquired tolerance to summer drought. Seedlings of the two species were grown from April to September in a plastic tunnel greenhouse and exposed to two irrigation regimes (control, 100% water holding capacity; water-stressed, 50% of control). In mid-August, the irrigation of all plants was suspended for three weeks. The response of the species was analyzed to evaluate survival, growth, ecological, and anatomical traits of wood produced under stressful conditions and marked through the pinning technique. The results suggest that both species show pre-acclimation to drought, with Q. ilex demonstrating a marked increase in survival percentage. This is likely due to a reduction in vessel size in response to previous water stress. In contrast, in A. unedo, the higher frequency of narrower vessels allowed safer water transport compared to Q. ilex, thus explaining the slight increase in survival. Overall results indicated that the two species adopt different strategies to overcome drought, providing valuable insights for managing seedlings in natural ecosystems and urban green spaces.

Phenotypic plasticity of water-related traits reveals boundaries to the adaptive capacity of a dominant European grass species under increased drought

The intensification of droughts due to climate change is a global concern, and many plant species face increasing water deficits. Understanding the role of phenotypic plasticity in plant adaptation to these changing conditions is crucial. This research focuses on Bromopsis erecta, a dominant perennial grass in European and Mediterranean grasslands, to predict its potential adaptation to climate change. We assessed plants from shallow and deep soils (i.e., with contrasting water reserves) of a Mediterranean rangeland in southern France, and tested the effect of six years of experimentally increased summer drought compared to the ambient conditions on plant traits, survival and abundance. In both field and common garden experiments, we measured water-related traits, including static traits under non-limiting water conditions, and dynamic traits, such as rates of trait variation during drought. Trait plasticity was determined as a reaction norm to increasing soil water stress and was tested against changes in B. erecta abundance over the past decade, including the study period. Trait plasticity was detected only for leaf dry matter content (LDMC), revealing that the resource strategy of B. erecta became more conservative over less than a decade with higher LDMC and leaf thickness according to the plant economic spectrum. No plasticity was found for osmotic potential or specific leaf area. The variability of other traits was ascribed to the possible lagging effect of previous water stress and was associated more with soil depth than with previous summer drought intensity. The abundance decline of B. erecta, which dropped from 20 % to around 5 % in shallow soils, was not associated with the plasticity of LDMC but was positively correlated with variations in leaf base membrane damage, meaning unexpectedly, that plants exposed to the most severe summer drought also had the most sensitive leaf base membranes, a possible sign of maladaptive trait plasticity in the population. This key trait response reveals boundaries to the adaptive capacity of this perennial grass to survive pluri-annual drought.

Estimating stomatal conductance and evapotranspiration of winter wheat using a soil-plant water relations-based stress index

Stomatal conductance, closely related to water flow in the soil-plant-atmosphere continuum, is an important parameter in the Penman-Monteith (P-M) model for estimating evapotranspiration (ET). In this study, a novel soil water stress index ω, considering intrinsic soil-plant water relations, was introduced into the Jarvis empirical estimation model of stomatal conductance to improve the representation of the effect of soil water stress on stomatal conductance. The index ω accounted not only for current water availability by combing the effects of relative distribution of soil water to roots and nonlinear stomatal response, but also for the hysteresis effect of water stress by means of the inclusion of a recovery coefficient. Combined plant and soil-based measurements from a greenhouse experiment provided the basis for investigating the relationship between leaf stomatal conductance gs and root zone soil water stress represented by ω. The response of gs to root-weighted soil matric potential was found to be nonlinear. The relationship between gs and the extent of previous water stress (i.e. the water stress recovery coefficient curve) was generalized by a power function and was verified and confirmed using results obtained from the literature. The reliability of ω was tested by coupling it into the Jarvis model to estimate leaf (gs) and canopy (gc) stomatal conductance, and thereupon into the P-M model to estimate cumulative ET (CET) in the greenhouse experiment and two field experiments. The estimated gs, gc and CET agreed well with the measurements, with root mean squared error not more than 0.0006 m s−1, 0.0020 m s−1 and 8.2 mm, respectively, and determination coefficient (Nash-Sutcliffe efficiency coefficient) consistently greater than 65% (0.14). Therefore, ω should be feasible and reliable to delineate the response of stomatal physiological reaction to water stress, and hence helpful for accurate estimation of ET using Jarvis-based P-M models.

Effect of water stress “memory” on plant behavior during subsequent drought stress

Frequency of extreme drought events are expected to increase due to climate change. Perennials are increasingly exposed to recurrent drought during their life span. The aim of the present work was to study the effect of recurrent droughts on the behavior of Vitis vinifera under water stress. Sangiovese and Montepulciano vines were exposed to severe drought stress for 4 years (WS-S). A dry-down experiment was carried out to compare their behavior with a set of vines kept at 90% field capacity during the whole seasons in the previous 4 years (WW-S). WS-S vines had higher transpiration and stomatal conductance than WW-S vines. Net photosynthesis was almost unaffected by the treatment. Stomatal conductance was higher at more negative Ψstem in WS-S vines than in control vines. Leaf petiole percentage loss of hydraulic conductance, measured during water stress, was higher in WS-S than in WW-S vines. Results indicate that previous water stress can lead to less conservative plant strategy toward water loss and decreased water use efficiency. This behavior seems to be coordinated with the different stomatal response to decreasing water potential that caused a reduction of xylem hydraulic safety margin in WS-S vines in comparison with WW-S vines.

Molecular responses to recurrent drought in two contrasting rice genotypes.

The set of variables analyzed as integrated by multivariate analysis of principal components consistently showed a memory effect induced by the drought pre-treatment in AN Cambará plants. The effects of drought can vary ddepending on many factors. Among these the occurrence of a previous water stress may leave a residual effect (memory), influencing the future performance of a plant in response to a new drought event. This study tested the hypothesis that plants experiencing recurrent drought would show more active mechanisms of water deficit tolerance, mainly plants of the genotype that is cultivated often experiencing water shortages periods. Additionally, all the plants subjected to water deficit were rehydrated by 24h and the expression of transcription factors related to drought responses was re-evaluated. To this end, the water status of two rice genotypes, BRS Querência (flooded) and AN Cambará (dryland), was evaluated to identify molecular alterations likely underpinning drought-memory. In growth stage V5, some plants were exposed to water stress (10% VWC soil moisture-pre-treatment). Thereafter, the pots were rehydrated at the same level as the control pots and maintained under this condition until drought was reapplied (10% VWC) at the reproductive stage (R1-R2). Then, the plants were rehydrated and maintained at pot capacity for 24h. Overall, the set of variables analyzed integrally by multivariate analysis of principal components consistently showed a memory effect induced by the drought pre-treatment in AN Cambará plants (the dryland genotype). This conclusion, based on data of the biochemical and molecular analyses, was supported by the greater capacity of maintenance of the water status by stomatal regulation of the pre-treated and rehydrated plants after the second drought stimulus.

Drought stress memory in the photosynthetic mechanisms of an invasive CAM species, Aptenia cordifolia.

Plants are known for their high capacity to acclimatise to fluctuating environmental conditions. A wide range of environmental conditions can lead to suboptimal physiological efficiency. However, recent studies have shown that plants can withstand repeated periods of stress. To find out how they do it, we studied photosynthetic adjustments to repeated water stress in Aptenia cordifolia: a facultative, invasive CAM species. Plants were subjected to three cycles of water deficit, and photosynthetic parameters and chloroplast antioxidants were quantified to gain an understanding of the mechanisms by which they cope with repeated stress periods. Significant modification of the photosystems' antenna and reaction centres was observed in plants subjected to previous water stress cycles, and this led to higher PSII efficiency than in plants challenged with drought for the first time. These findings underline the biological significance of stress memory and show how plants can adjust their photosynthetic apparatus to fluctuating environmental conditions and thus optimise photosynthesis and photoprotection under drought conditions.

Short episodes of water stress increase barley root resistance to radial shrinkage in a dehydrating environment

Although plant shoots can be ‘hardened’ by abiotic stresses, little is known about such changes in roots. In order to investigate possible induction of root‐hardening in response to short water‐stress episodes, barley seedlings (Hordeum vulgare L) hydroponically grown under a controlled environment were moderately water‐stressed by addition of a non‐penetrating osmoticum, polyethylene glycol (PEG) 6000 at −0.4 MPa water potential, to the aerated nutrient solution. Seedlings were then hydrated in dilute nutrient solution without PEG before excision and assay of the seminal roots. Previous water stress treatments for 72 h, 12 h, or even 6 h induced an apparent root‐hardening process. Thus, root radial shrinkage during subsequent exposure to strongly dehydrating conditions was remarkably decreased. The root hardening was related to biophysical adjustments: turgor‐pressure increased while osmotic potential decreased from −0.45 ± 0.02 MPa to −0.60 ± 0.02 MPa. Moreover, the maximum bulk volumetric modulus of elasticity, ?max determined by pressure–volume analysis, increased from 2.1 ± 0.4 MPa to 3.7 ± 0.4 MPa, i.e. root elasticity was decreased. Root hardening in response to episodes of water stress may have ecological significance for barley plants in regions where intermittent drought episodes are frequent.

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.

Effects of Previous Water Stress Treatment on the Leaf Photosynthesis and Related Factors in Oats (C_3) and Maize (C_4)

Effects of Previous Water Stress Treatment on the Leaf Photosynthesis and Related Factors in Oats (C_3) and Maize (C_4)

Effects of exposure to ozone and water stress on the following season's growth of beech (Fagus sylvatica L.).

Bud break and growth of beech trees were measured during the growing season of 1992. The trees had previously been exposed, through the growing season of 1991, to one of four treatments: (1) episodic ozone for 128 d, total dose = 46-3 ppm h; (2) air purified by filtration through Purified and charcoal; (3) ozone together with a period of water shortage: (4) filtered air with a period of water shortage. Despite uniform growth conditions during 1992. the previous water stress treatment caused bud break to begin slightly earlier, but the rates of shoot growth and the length of the first flush branches were reduced (40%). In well-watered plants ozone caused a reduced Tate of shoot growth during the first week after bud break. The total amount of growth during 1992 was shown to be reduced (36%) by the previous water stress treatment, In the case of the well-watered trees, exposure to ozone in the previous year reduced the amount of new growth by 17%, which was the result of reduced internal expansion. When ozone was combined with water stress, there was no further reduction in the amount of new growth, but there was a fall in the number of internodes relative to water-stressed plants grown in filtered air. Ozone and water stress applied singly reduced growth. A combination of the two stresses, however, caused no additional reduction in growth, but reduced the number of internodes. The possible implications of the aftereffects of these stresses are discussed in relation to reduced productivity and canopy structure.

Root Dynamics of Bouteloua gracilis During Short-Term Recovery from Drought

1 The ability of drought-stressed Bouteloua gracilis H.B.K. Lag. ex Steud. to respond rapidly to a small rainfall event with increases in leaf water potential and leaf conductance directed our attention to the role of the roots in these responses. Our first objective was to determine whether new root growth was required to restore the water status to that of a non-stressed plant, following a small rainfall event. The results indicated that surviving roots were able to absorb water at approximately 40% of the rate of new roots, which was sufficient to restore non-stressed leaf water potentials within one day of watering. 2 The second objective was to estimate the rate and amount of new root growth following simulated rainfall events. New root growth occurred approximately 40h after watering. New roots never accounted for more than 15% of total root length but they made possible the continued response to increased water availability. 3 The third objective was to evaluate the importance of previous water stress in the response of Bouteloua gracilis to watering. The response of leaf water potential was influenced by previous water stress as well as by the amount of water added. However, the response of root growth was independent of water stress when 15 mm of water was added and dependent upon water stress in the case of the addition of only 5 mm. *On leave from Departamento de Ecologfa, Facultad de Agronomfa, Universidad de Buenos Aires, Avenida San Martin 4453, Buenos Aires 1417, Argentina. Correspondence: W. K. Lauenroth, Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, Colorado 80523, USA. 4 A simulation analysis of potential carbon gain, as a result of Bouteloua gracilis responding to a 5-mm rainfall event, suggested that the cost of producing new roots was less than the gain. Key-words: Drought, Bouteloua, root growth, steppe region, C4

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.

Modulation of aversively motivated learning in rats adapted to a cold stressor

Two experiments studied effects of adaptation to cold water stress upon learning in two aversively motivated (shock) tasks. Experiment 1 found animals previously experiencing cold water stress exhibited more tolerance to shock, having shorter latencies, in an approach-avoidance conflict situation than non-treated controls. In Experiment 2, animals with previous cold water stress experience exhibited longer response latencies than controls in an active-avoidance task. These findings provide evidence that adaptation to a noncontingent stressor can modulate behavioral responses which suggest increased tolerance.

Morphological and physiological changes in black alder induced by water stress

Abstract. Black alder seedlings were exposed to 12 weeks of sublethal water stress by watering only when visibly wilted. Control seedlings were watered regularly throughout the treatment period. Stressed seedlings exhibited significant osmotic adjustment of over 0.4 MPa. The water stress treatment also significantly reduced leaf size, increased epicuticular wax content, and increased the root shoot ratio. The response of leaf conductance to decreasing leaf water potential was influenced by the previous water stress treatment Stressed seedlings had a much lower initial leaf conductance, but showed a gradual drop in leaf conductance as leaf water potential decreased; whereas, control seedling leaf conductance fell rapidly. These morphological and physiological modifications in response to moisture stress have the potential for significantly improving black alder drought tolerance.

Investigations of ripeness to flower in tobacco

The physiology of ripeness to flower, as it applies to the development of the tobacco crop, was studied through the use of grafting and defoliation techniques. Young tobacco plants raised in controlled conditions known to promote floral induction did not reach ripeness to flower until, at the earliest, the unfolding of the third true leaf. The cotyledons and first two leaves were alone unable to induce flowering. The inductive ability of the third and successive leaves was lost rapidly with age, but did not appear to be affected by previous water stress. The morphologically juvenile shoot apices of field seedlings could readily be induced to flower, when grafted on to suitable stocks, long before they were able to do so intact. The expanded leaves of field seedlings lacked the ability to induce flowering, despite their apparently adequate size. They influenced flowering only indirectly through their contribution to the growth of those higher leaves that unfold upon recovery from transplanting, which are the first leaves fully able to induce flowering, and which appear to be actually responsible for induction under normal conditions. The inability of expanded leaves of seedbed plants to induce flowering was attributed primarily to the loss of inductive ability with age although the possibility that cultural treatments affect hormonal status cannot be dismissed. Evidence is presented to support the view that leaf expansion in the seedbed is commonly so slow that for long periods there is insufficient area of young leaf to promote floral induction.

INFLUENCE OF SOIL WATER STRESS ON WILTING AND WATER RELATIONS OF DIFFERENTLY OSMOTICALLY ADJUSTED WHEAT PLANTS

SummaryDuring a pretreatment period of 1 week, spring wheat plants (Triticum aestivum, L., cv. ‘Sappo’) grown in a sandy soil in pots were adjusted to three levels of soil water osmotic potential induced by watering the plants with a nutrient solution (minus 0·5 bar) and further additions of KNO3 (minus 3 and minus 6 bar). After leaching of the soil, the plants were exposed to two drying cycles separated by rewetting. With severe water stress at the end of drying cycle 1, reduction of wilting was highly correlated with lowering of leaf osmotic potential due to the KNO3pretreatment. Turgor potential was highest and decreased at lowest soil water matric potentials in KNO3 pretreated plants. Recovery after rewatering was seemingly most accelerated in KNO3 pretreated plants due to a larger potential difference between leaf and soil water. The leaf and soil water matric potentials at which stomata closed were lowered as a result of both KNO3 pretreatment and the effect of previous water stress on leaf osmotic potential.

Hydraulic Resistance of Rough Lemon Roots

AbstractA pressure chamber technique was used to estimate hydraulic root resistance in rough lemon (Citrus jambhiri Lush.) seedlings. The effect of previous water stress on hydraulic root resistance was evaluated. A factorial 3 × 3 design with four replications was established with potted rough lemon seedlings in a growth chamber. Three water‐stress treatments were applied by watering at intervals of 1, 2 and 3 days, and root resistance measurements were made after 6, 12 and 18 days of treatment. Plants that had experienced mild and severe water stress (irrigation interval of 2 and 3 days, respectively) had higher hydraulic root resistances after several drying cycles than those plants irrigated daily. Additional cycles had no significant effect. The increase in root resistance was not due to decreased root growth but apparently to changes in the permeability of the root cell membranes or to increased suberin deposition in the cell walls of the cortical cells. In a short‐term experiment (1 h), temperature strongly affected water flow through rough lemon roots in the range 5 to 35°C. Temperature influenced root membrane permeability, since reduced blow could not be explained by changes in water viscosity.

Stomatal Response to Leaf Water Potential as Affected by Preconditioning Water Stress in the Field1

AbstractPrevious research has shown that stomatal response to decreasing soil water potential of chamber‐grown sorghum (Sorghum bicolor L. Moench. ‘Oro’) and cotton (Gossypium hirsutum L. ‘Stoneville 213’) is altered by exposure to previous water stress. This work was undertaken to determine if stomatal response of field‐grown plants is also altered by previous water stress.Stoneville 213 cotton was grown in the field under movable rainshelters and was subjected to three treatments: control — well watered, one period of water stress, and two periods of water stress. After this preconditioning period, all plants underwent a final stress during which stomatal response to leaf water potential was measured.The periods of preconditioning water stress were characterized by decreased cumulative growth as measured by leaf area per plant. Leaf areas for the control, one soil water stress plants, and two soil water stress plants were 5,200, 2,200, and 1,200 cm2, respectively. Lower stomates of preconditoned field‐grown plants remained open to lower leaf water potentials (—28 to —30 bars) during the final stress than those of plants which were not preconditioned (—22 bars). These results were similar to those found previously on chamber‐grown plants which had been exposed to more frequent but shorter stresses. The 6 to 8 bar adjustment in leaf water potential vs. stomatal resistance as a result of previous water stress indicates a need for caution in interpreting data from plants of unknown water stress history.

Effect of Water Stress on Proline Synthesis from Radioactive Precursors

Barley (Hordeum vulgare L. var. Prior) leaves converted more (14)C-glutamic acid to free proline when water-stressed than when turgid; neither decreased protein synthesis nor isotope trapping by the enlarged free proline pools found in wilted tissue seemed to account for the result. This apparent stimulation of proline biosynthesis in wilted leaves was not observed when radioactive ornithine or P5C (Delta(1)-pyrroline-5-carboxylate, an intermediate following glutamate in proline synthesis) were used as proline precursors unless proline levels were high as a result of previous water stress. We interpret this to mean that any stimulation of proline synthesis by water stress must act on P5C formation rather than its reduction to proline. Experiments showing greater apparent conversion of (14)C-glutamate to proline do not unequivocally prove that proline synthesis is stimulated by water stress, as P5C feeding studies show that proline oxidation is inhibited under comparable conditions. This inhibition could account, at least in part, for increased proline labeling, and must be considered an alternate possibility.

Effect of Previous Water Stress on Ion Uptake and Transport in Barley Seedlings

Measurements of ion transport through roots and ion uptake into roots were made following a brief period of water stress induced by wilting in air. The basic processes of photosynthesis, respiration and protein sinthesis did not appear to be affected by this treatment, and uptake of 86Rb and L-leucine to the roots was not reduced. However, transport of 86Rb and L-leucine from root to shoot wasinhibited. Thus the response of the plants to water stress resembles the response to inhibitors of protein synthesis and to abscisic acid, which has been found to be produced in plants subject to water stress.