Leaf Relative Water Research Articles

Leaf mechanisms involved in the response of Cydonia oblonga trees to water stress and recovery

Quince tree (Cydonia oblonga Mill.) is known for bearing fruits that are rich in nutrients and health-promoting compounds while requiring low inputs of agrochemicals, and maintenance, but no information exists on the mechanisms developed at the level of leaf water relations to confront water stress and recovery. For this reason, the purpose of the present study was to identify the strategy (isohydric or anisohydric) by which quince plants cope with water stress and to further elucidate the resistance mechanisms developed in response to water stress and during recovery. In summer 2016, field-grown own rooted 17-years old quince trees (cv. BA-29) were subjected to two irrigation treatments. Control (T0) plants were drip irrigated (105% ETo) to ensure non-limiting soil water conditions, while T1 plants were irrigated at the same level as used in T0, except that irrigation was withheld for 42 days during the linear fruit growth phase, after which irrigation returned to the levels of T0 (recovery period). During the experimental period, T0 and T1 received a total of 374 and 143 mm water, respectively, including rain water. The quince trees exhibited extreme anisohydric behaviour under the experimental conditions. As water stress developed and during the recovery period, the plants exhibited high hydraulic conductivity, probably the result of resistance to cavitation. From the beginning of water stress to the time of maximum water stress, leaf turgor was maintained, possibly due to active osmotic adjustment (stress tolerance mechanism). This leaf turgor maintenance may have contributed to the high leaf conductance, and, therefore, good leaf productivity. The low quince leaf apoplastic water fraction under water stress could be considered as another drought tolerance characteristic because if the accumulation of water in the apoplasm is avoided a steeper gradient in water potential between the leaf and the soil can take place under water stress, thus favouring water absorption.

A Protein-Linger Strategy Keeps the Plant On-Hold After Rehydration of Drought-Stressed Beta vulgaris.

Most crop plants are exposed to intermittent drought periods. To cope with these continuous changes, plants need strategies to prevent themselves from exhaustive adjustment maneuvers. Drought stress recovery has been shown to be an active process, possibly involved in a drought memory effect allowing plants to better cope with recurrent aridity. An integrated understanding of the molecular processes of enhanced drought tolerance is required to tailor key networks for improved crop protection. During summer, prolonged periods of drought are the major reason for economic yield losses of sugar beet (Beta vulgaris) in Europe. A drought stress and recovery time course experiment was carried out under controlled environmental conditions. In order to find regulatory key mechanisms enabling plants to rapidly react to periodic stress events, beets were either subjected to 11 days of progressive drought, or were drought stressed for 9 days followed by gradual rewatering for 14 days. Based on physiological measurements of leaf water relations and changes in different stress indicators, plants experienced a switch from moderate to severe water stress between day 9 and 11 of drought. The leaf proteome was analyzed, revealing induced protein pre-adjustment (prior to severe stress) and putative stress endurance processes. Three key protein targets, regulatory relevant during drought stress and with lingering levels of abundance upon rewatering were further exploited through their transcript performance. These three targets consist of a jasmonate induced, a salt-stress enhanced and a phosphatidylethanolamine-binding protein. The data demonstrate delayed protein responses to stress compared to their transcripts and indicate that the lingering mechanism is post-transcriptionally regulated. A set of lingering proteins is discussed with respect to a possible involvement in drought stress acclimation and memory effects.

Leaf water relations in Diospyros kaki during a mild water deficit exposure

The resistance mechanisms (stress avoidance and stress tolerance) developed by persimmon plants (Diospyros kaki L. f. grafted on Diospyros lotus L.) in response to mild water stress and the sensitivity of continuously (on a whole-day basis) and discretely (at predawn and midday) measured indicators of the plant water status were investigated in 3-year old ‘Rojo Brillante’ persimmon plants. Control (T0) plants were drip irrigated in order to maintain soil water content at levels slightly above soil field capacity (102.3% of soil field capacity) and T1 plants were drip irrigated for 33 days in order to maintain the soil water content at around 80% of soil field capacity. The results indicated persimmon plants confront a mild water stress situation by gradually developing stomata control (stress avoidance mechanism) and exhibiting some xeromorphic characteristic such as high leaf relative apoplastic water content, which could contribute to the retention of water at low leaf water potentials. In addition, sap flow measurements made by the heat-pulse technique were seen to be the most suitable method for estimating persimmon water status, because it provided the highest signal intensity (actual value/reference value):noise (coefficient of variation) ratio in almost all intervals of time considered and provides continuous and automated registers of the persimmon water status in real time.

Novel Miscanthus genotypes selected for different drought tolerance phenotypes show enhanced tolerance across combinations of salinity and drought treatments.

Background and AimsWater deficit and salinity stresses are often experienced by plants concurrently; however, knowledge is limited about the effects of combined salinity and water deficit stress in plants, and especially in C4 bioenergy crops. Here we aim to understand how diverse drought tolerance traits may deliver tolerance to combinations of drought and salinity in C4 crops, and identify key traits that influence the productivity and biomass composition of novel Miscanthus genotypes under such conditions.MethodsNovel genotypes used included M. sinensis and M. floridulus species, pre-screened for different drought responses, plus the commercial accession Miscanthus × giganteus (M×g.). Plants were grown under control treatments, single stress or combinations of water deficit and moderate salinity stress. Morphophysiological responses, including growth, yield, gas exchange and leaf water relations and contents of proline, soluble sugars, ash and lignin were tested for significant genotypic and treatment effects.Key ResultsThe results indicated that plants subjected to combined stresses showed more severe responses compared with single stresses. All novel drought-tolerant genotypes and M×g. were tolerant to moderate salinity stress. Biomass production in M. sinensis genotypes was more resilient to co-occurring stresses than that in M×g. and M. floridulus, which, despite the yield penalty produced more biomass overall. A stay-green M. sinensis genotype adopted a conservative growth strategy with few significant treatment effects. Proline biosynthesis was species-specific and was triggered by salinity and co-occurring stress treatments, mainly in M. floridulus. The ash content was compartmentalized differently in leaves and stems in the novel genotypes, indicating different mechanisms of ion accumulation.ConclusionsThis study highlights the potential to select novel drought-tolerant Miscanthus genotypes that are resilient to combinations of stress and is expected to contribute to a deeper fundamental knowledge of different mechanistic responses identified for further exploitation in developing resilient Miscanthus crops.

Fortified fertilizer application in wheat (Triticum aestivum L.) grown under water stress condition

Abstract Water stress is a major threat against wheat growth. The effects of induced stress can be reduced after by fortified fertilizer treated by Plant Growth Promoting Bacteria (PGPB). With the objective to combat the water stress, two different experiments under net house and field condition were conducted. Three different states of fertilizer [F0: Control (no fertilizer application); F1: PGPB-coated fertilizer (urea and phosphorous) &F2: uncoated fertilizer (urea and phosphorous)]. In a pot experiment, wheat plants were applied fertilizer in raised and well-watered (60 percent of field capacity) and water stressed (40 percent of field capacity) conditions in soil filled pots. In experiment-II (field study), similar treatments of fertilizer were revised, but well-watered and water stress treatments/plots were irrigated for 60 seconds and 30 seconds respectively. At maturity plants were harvested and various morphological (number of tillers/plant, number of spikelet/spike, number of grains/spike, weight of grains, biological yield, economic yield and harvest index) and biochemical parameters (leaf nitrogen, phosphorous & potassium contents) of crop were recorded. Leaf chlorophyll and relative water contents of crop were also measured 60 days after sowing. In this study, it was demonstrated that the water stress adversely affected all the above mentioned parameters. The PGPB coated fertilizer application in wheat significantly increased (p<0.01 for pot and p<0.05 for field study) morphological and biochemical parameters in the presence and absence of water stress both under net house and field conditions. We can conclude from these findings that application of PGPB coated fertilizer is valuable strategy to mitigate the water stress impact on wheat with improved yield. Keywords: Coated fertilizer; Un-coated fertilizer; PGPB; Chlorophyll; Harvest inde http://dx.doi.org/10.19045/bspab.2019.80037

Adjustments and coordination of hydraulic, leaf and stem traits along a water availability gradient.

Trait variability in space and time allows plants to adjust to changing environmental conditions. However, we know little about how this variability is distributed and coordinated at different organizational levels. For six dominant tree species in northeastern Spain (three Fagaceae and three Pinaceae) we quantified the inter- and intraspecific variability of a set of traits along a water availability gradient. We measured leaf mass per area (LMA), leaf nitrogen (N) concentration, carbon isotope composition in leaves (δ13 C), stem wood density, the Huber value (Hv, the ratio of cross-sectional sapwood area to leaf area), sapwood-specific and leaf-specific stem hydraulic conductivity, vulnerability to xylem embolism (P50 ) and the turgor loss point (Ptlp ). Differences between families explained the largest amount of variability for most traits, although intraspecific variability was also relevant. Species occupying wetter sites showed higher N, P50 and Ptlp , and lower LMA, δ13 C and Hv. However, when trait relationships with water availability were assessed within species they held only for Hv and Ptlp . Overall, our results indicate that intraspecific adjustments along the water availability gradient relied primarily on changes in resource allocation between sapwood and leaf area and in leaf water relations.

Investigating the effect of Azospirillum brasilense and Rhizobium pisi on agronomic traits of wheat (Triticum aestivum L.)

ABSTRACTPlant growth-promoting rhizobacteria (PGPR) play an important role in improving crop growth but have not been studied sufficiently. A wire house experiment was conducted in Pakistan to determine the combined effect of inoculating wheat seeds with PGPR on the subsequent growth and yield of the wheat. The experiment included four treatments: T0 – no-inoculation (control), T1 – Azospirillum brasilense inoculation, T2 – Rhizobium pisi inoculation and T3 – co-inoculation with A. brasilense and R. pisi. Development and growth attributes, as well as final yield of wheat, were studied. Co-inoculation of seeds with both strains increased significantly wheat grain yield, the number of grains per plant and 1000-grain weight by 36%, 11% and 17%, respectively, compared to non-inoculated control. While crop growth rate increased for, respectively, 5.5% and 33% at tillering and flag leaf stages, corresponding values for T3 were about 9% and 14% higher than values for sole inoculations in T1 and T2. Co-inoculation also significantly increased leaf epicuticular wax and relative water content as compared to the control treatment. Thus, inoculation of wheat seeds with A. brasilense and R. pisi and their combination is a promising method to improve growth, yield and quality of wheat.

The Smaller the Leaf Is, the Faster the Leaf Water Loses in a Temperate Forest.

Leaf size (i.e., leaf surface area and leaf dry mass) profoundly affects a variety of biological carbon, water and energy processes. Therefore, the remarkable variability in individual leaf size and its trade-off with total leaf number in a plant have particularly important implications for understanding the adaption strategy of plants to environmental changes. The various leaf sizes of plants growing in the same habitat are expected to have distinct abilities of thermal regulation influencing leaf water loss and shedding heat. Here, we sampled 16 tree species co-occurring in a temperate forest in northeastern China to quantify the variation of leaf, stomata and twigs traits, and to determine the relationships of leaf size with leaf number and leaf water loss. We examined the right-skewed distributions of leaf size, leafing intensity, stomatal size and stomatal density across species. Leafing intensity was significantly negatively correlated with leaf size, accounting for 4 and 12% of variation in leaf area and leaf mass, respectively. Species was the most important factor in explaining the variation in leaf size (conditional R2 of 0.92 for leaf area and 0.82 for leaf mass). Leaf area and mass significantly increased with increasing diameter of twigs. Leaf water loss was strongly negatively correlated with leaf area and leaf mass during the first four hours of the measurement. Leaf area and leaf mass accounted for 38 and 30% of variation in total leaf water loss, respectively. Leaf water loss rate (k) was significantly different among tree species and markedly linearly decreased with increasing leaf area and leaf mass for simple-leaved tree species. In conclusion, the existence of a cross-species trade-off between the size of individual leaves and the number of leaves per yearly twig unit was confirmed in that temperate forest. There was strongly negative correlation between leaf water loss and leaf size across tree species, which provides evidences for leaf size in leaf temperature regulation in dry environment with strong radiation. The size-dependent leaf water relation is of central importance to recognize the functional role of leaf size in a changing climate including rapid changes in air temperature and rainfall.

An endophytic isolate of the fungus Yarrowia lipolytica produces metabolites that ameliorate the negative impact of salt stress on the physiology of maize

BackgroundTo combat salinity, plants need easily accessible, safe and sustainable mechanisms for optimum growth. Recently, endophytes proved to be the promising candidates that helped the host plant to thrive under stress conditions. Therefore, the aim was to discover endophytic strain(s) and their mechanism of action to alleviate salt stress in maize.ResultsKeeping the diverse role of endophytes in view, 9 endophytic fungi from the spines of Euphorbia milli L. were isolated. Among the isolated fungal isolates, isolate FH1 was selected for further study on the basis of high antioxidant activity and capability to produce high indole-3-acetic acid (IAA), indole-3-acetamide (IAM), phenol and flavonoid contents. The 18S rDNA sequence homology and phylogenetic analysis of the fungal isolate FH1 revealed to be Yarrowia lipolytica. Furthermore, the inoculation of Y. lipolytica FH1 had significantly promoted plant growth attributes in treated maize as compared to positive (salt stress) and negative (salt stress free) controls. Likewise, differences in chlorophyll, carotenes, electrolyte leakage, leaf relative water, peroxidase, catalase, ABA, IAA and proline contents were observed between treated maize and controls. Interestingly, Y. lipolytica FH1 inoculated plants showed lower endogenous ABA and higher endogenous IAA contents.ConclusionFrom the results, we have concluded that Y. lipolytica inoculation has promoted the growth of maize plants through controlled metabolism and hormonal secretions (ABA and IAA) under salinity stress. Because of the fact, Y. lipolytica can be tried as an eco-friendly bio-fertilizer to achieve optimum crop productivity under saline conditions.

Impact of foliar fertilization on apple and pear trees in reconciling productivity and alleviation of environmental concerns under arid conditions

ABSTRACTDrought and heat stress are significant factors limiting fruit crop yield in arid conditions. Foliar fertilization is a common practice of supplying fruit crop production with mineral nutrients, especially under limited soil nutrient availability conditions. To evaluate potential effectiveness of the foliar application of macro-, micronutrient and growth regulators on dynamics of physiological parameters of the pear and apple cultivars under abiotic stresses, three–year experiments were carried out under arid conditions at the Russian Research Institute of Arid Agriculture during the 2015–2017 growing seasons. It has been revealed that foliar nutrition reduces the negative influence of heat stress, stabilizes the functional state of plants, thereby enhancing resistance to drought. During the most severe drought periods of vegetation, under the influence of foliar nutrition, there was a significant increase in the total water content (TWC), relative leaf turgidity (RLT) and water retention capacity (WRC); and also index of leaf water deficiency (LWD) was improved as compared to the non-treated control. All foliar treatments involving the macro-, micronutrient and growth regulators significantly enhanced fruit crop yield of pear and apple varieties over the control, yield enhancement was obtained 2.7–22.0 t ha−1 for the Talgar beauty (pear variety), 2.2–19.3 t ha−1 for the Renet Symirenko (apple variety), and 1.6–10.5 t ha−1 for the Starkrimson (apple variety). The most effective treatments for water consumption coefficient (WCC) were plantafol and speedphol. The results suggest that foliar plantafol and speedfol could be used as part of an efficient, sustainable fertilizer program for apple and pear trees for maintaining or improving fruit quality, productivity, and avoiding negative efficacy of abiotic stresses.

Evaluation of Leaf-Water Relation Traits, as Selection Criterion for Developing Drought Resistant Potato (Solanum Tuberosum L.) Genotypes

Evaluation of Leaf-Water Relation Traits, as Selection Criterion for Developing Drought Resistant Potato (Solanum Tuberosum L.) Genotypes

Temperature induced shifts in leaf water relations and growth efficiency indicate climate change may limit aspen growth in the Colorado Rockies

Higher temperatures and evaporative demand forecasted for Colorado forests by the end of the century suggest that soil water limitation increasingly will negatively impact whole plant performance. At the same time, upslope or poleward migration of plant ranges in response to warming may result in species experiencing cooler overnight temperatures, particularly if extremes in climate increase. In 2014 we established three experimental gardens along a temperature/elevation gradient to test the implications of shifting temperatures on tree function. Quaking aspen (Populus tremuloides) seedlings from a mid-elevation population were established in all three gardens and leaves were sampled monthly during the 2017 growing season. From these, we quantified the magnitude and timing of osmotic regulation, the relationships between leaf osmotic potential (Ψosm), midday leaf water potential (Ψmid), and soil moisture conditions under different temperature regimes, and growth efficiency (change in basal area/growing day). We observed a strong relationship between Ψosm and soil moisture, and a strong seasonal decline in Ψosm at the warmest and intermediate sites while the coldest site experienced a later increase in osmolytes associated with the highest degree of freeze tolerance. Growth efficiency was highest at the intermediate-temperature site – closest in elevation to the seed source location – but declined asymmetrically with warming or cooling. The novel abiotic conditions at both non-local sites resulted in declines in growth efficiency, suggesting that aspen will experience suboptimal conditions whether it stays in areas experiencing warming temperatures or if it migrates upslope to areas with colder overnight temperatures.

Water relations determine short time leaf growth patterns in the mangrove Avicennia marina (Forssk.) Vierh.

High-resolution leaf growth is rarely studied despite its importance as a metric for plant performance and resource use efficiency. This is in part due to methodological challenges. Here, we present a method for in situ leaf growth measurements in a natural environment. We measured instantaneous leaf growth on a mature Avicennia marina subsp. australasica tree over several weeks. We measured leaf expansion by taking time-lapse images and analysing them using marker tracking software. A custom-made instrument was designed to enable long-term field studies. We detected a distinct diel growth pattern with leaf area shrinkage in the morning and leaf expansion in the afternoon and at night. On average, the observed daily shrinkage was 37% of the net growth. Most of the net growth occurred at night. Diel leaf area shrinkage and recovery continued after growth cessation. The amount of daily growth was negatively correlated with shrinkage, and instantaneous leaf growth and shrinkage were correlated with changes in leaf turgor. We conclude that, at least in this tree species, instantaneous leaf growth patterns are very strongly linked to, and most likely driven by, leaf water relations, suggesting decoupling of short-term growth patterns from carbon assimilation.

Petiole gall aphid (Pemphigus spyrothecae) infestation of Populus × petrovskiana leaves alters foliage photosynthetic characteristics and leads to enhanced emissions of both constitutive and stress-induced volatiles.

Poplar spiral gall aphid (Pemphigus spyrothecae) forms galls on the petiole in poplars (Populus) and mass infestations are frequent in poplar stands, but how these parasite gall infestations can affect the leaf lamina structure, photosynthetic rate and constitutive and stress volatile emissions is unknown. We investigated how the infestation by the petiole gall aphids affects lamina photosynthetic characteristics (net assimilation rate, stomatal conductance), C and N contents, and constitutive isoprene and induced volatile emissions in Populus × petrovskiana. The dry gall mass per leaf dry mass (M g/M l) was used as a quantitative measure of the severity of gall infestation. Very high fraction of leaf biomass was invested in gall formation with M g/M l varying between 0.5-2. Over the whole range of the infestation severities, net assimilation rate per area, leaf dry mass per unit area and N content decreased with increasing the severity of infestation. In contrast, stomatal conductance, leaf dry mass per fresh mass, constitutive isoprene emissions, and induced green leaf volatile (GLV), monoterpene, sesquiterpene and benzenoid emissions increased with increasing the severity of gall infestation. The rates of induced emissions were low and these emissions were associated with methyl jasmonate release from leaf laminas. The data demonstrate that petiole gall infestations lead to major changes in leaf lamina sink-source relationships and leaf water relations, thereby significantly altering lamina photosynthesis. Modifications in stress-induced emissions likely indicated systemic signaling triggered by jasmonate transported from the petiole galls to the lamina where jasmonate elicited a cascade of volatile emission responses. Enhance isoprene emissions and induced volatile emissions can play a major role in indirect defense against other herbivores, securing the food source for the gall aphids. In conclusion, a massive infestation by petiole gall aphids can profoundly modify the foliage photosynthetic performance and volatile emission profiles in poplars.

Prolonged drying cycles stimulate ABA accumulation in Citrus macrophylla seedlings exposed to partial rootzone drying

Partial rootzone drying (PRD) establishes discrete wet and dry parts of the rootzone (for example using parallel drip lines on either side of the crop row), and alternates them to stimulate root growth and root-to-shoot ABA signalling. To assess whether alternation frequency affects plant physiological responses, Citrus macrophylla Wester seedlings were grown with the root system split between two pots and 5 irrigation treatments applied: Control, PRD-Fixed (where wet and dry parts of the rootzone were not alternated) and three alternate PRD treatments where the wet and dry parts were swapped at 3 (PRD1), 6 (PRD2) and 12 (PRD3) days intervals, to dry the soil to different degrees before alternating the irrigation. Water was equally distributed between both pots in Control plants, whereas only one pot was watered and the other allowed to dry in PRD plants, with all plants receiving the same irrigation volume. After 24 days, soil water content (θv), leaf water potential (Ψleaf), root water potential (Ψroot), abscisic acid (ABA) concentration in roots ([ABA]root), leaves ([ABA]leaf) and shoot xylem sap ([X-ABA]shoot), biomass allocation and leaf area were measured. Higher soil water availability of the dry side (PRD1 and PRD2) had no significant effects on leaf water relations, ABA status and plant biomass allocation. However, increasing the duration of exposure of part of the root system to dry soil (PRD3 and PRD-Fixed) further decreased Ψroot and stimulated root ABA accumulation, while decreasing Ψleaf and increasing [ABA]leaf of PRD3 plants compared to the other treatments. Differences in physiological response between PRD3 and PRD-Fixed plants were attributed to differences in the proportion of root mass exposed to drying soil: PRD3 plants had a lower Ψleaf and a higher [ABA]leaf with a smaller proportion of their root mass in wet soil. Since long drying cycles were required to alter plant biomass allocation and physiological responses in PRD plants, these should be implemented in designing suitable PRD strategies for field application.

Fire increases drought vulnerability of Quercus alba juveniles by altering forest microclimate and nitrogen availability

Abstract Shifts in rainfall patterns due to climate change are expected to increase drought stress and mortality in forests. Natural and anthropogenic fire regimes are also changing, highlighting the need to understand the interactive effects of fire and drought on tree ecophysiological response and growth. Using rainout shelters, we imposed summer drought on natural and planted populations of Quercus alba juveniles located in periodically burned and unburned sites in Shawnee National Forest, IL, USA. A subset of planted juveniles was clipped to simulate topkill. We measured predawn leaf water potential (Ψpd), leaf gas exchange (Amax, gmax) and relative growth rate (RGR) across treatments to test two hypotheses: (H1) Fire reduces juvenile drought stress by improving water relations through increased root‐to‐shoot ratios after topkill, or (H2) fire exacerbates juvenile drought stress by promoting a warmer, drier microclimate or amplifying drought‐induced nitrogen (N) limitation. Burned stands had higher vapour pressure deficits and 13% lower soil inorganic N availability than unburned stands. Rainout shelters reduced soil moisture (0–45 cm) by 10%–24% relative to ambient conditions. Consistent with H2, small, natural resprouts in burned stands experienced greater drought stress than unburned juveniles, with a 7% decrease in leaf nitrogen content (LNC), a 21%–29% reduction in Amax and gmax and a 41% reduction in RGR under drought. Drought effects on unburned juveniles, in contrast, were limited to a 5% reduction in LNC and a neutral to positive effect on leaf gas exchange and RGR. Large natural juveniles were largely unaffected by drought. Recent resprouts (i.e., clipped, planted juveniles) experienced less drought stress than unclipped juveniles, providing partial support for H1. Collectively, these results suggest that resprouting after fire can temporarily improve leaf water relations until root‐to‐shoot ratios re‐equilibrate. In contrast, fire can exacerbate drought‐driven declines in the growth of small juveniles by both promoting a warmer, drier microclimate and intensifying N limitation. Our results suggest that despite the high drought tolerance of Quercus spp., fire‐driven changes to local microclimate and resource conditions could limit tree recruitment under future scenarios of rainfall variability. A plain language summary is available for this article.

Physiological and biochemical changes during drought and recovery periods at tillering and jointing stages in wheat (Triticum aestivum L.)

Defining the metabolic strategies used by wheat to tolerate and recover from drought events will be important for ensuring yield stability in the future, but studies addressing this critical research topic are limited. To this end, the current study quantified the physiological, biochemical, and agronomic responses of a drought tolerant and drought sensitive cultivar to periods of water deficit and recovery. Drought stress caused a reversible decline in leaf water relations, membrane stability, and photosynthetic activity, leading to increased reactive oxygen species (ROS) generation, lipid peroxidation and membrane injury. Plants exhibited osmotic adjustment through the accumulation of soluble sugars, proline, and free amino acids and increased enzymatic and non-enzymatic antioxidant activities. After re-watering, leaf water potential, membrane stability, photosynthetic processes, ROS generation, anti-oxidative activities, lipid peroxidation, and osmotic potential completely recovered for moderately stressed plants and did not fully recover in severely stressed plants. Higher photosynthetic rates during drought and rapid recovery after re-watering produced less-pronounced yield declines in the tolerant cultivar than the sensitive cultivar. These results suggested that the plant’s ability to maintain functions during drought and to rapidly recover after re-watering during vegetative periods are important for determining final productivity in wheat.

Impact of nitrogen supply on leaf water relations and physiological traits in a set of potato (Solanum tuberosumL.) cultivars under drought stress

AbstractImproved adaptation of potato to limited water availability is needed for stable yields under drought. The maintenance of the cell water status and protection of cellular components against dehydration are important for drought tolerance, and the N status of plants affects the regulation of various respective metabolic processes. A 2‐year pot trial with 17 potato cultivars was conducted under a rain‐out shelter including two water regimes and two N‐levels to investigate genotypic differences concerning osmotic adjustment (OA) and relevant biochemical traits in relation to nitrogen (N) supply. Drought stress resulted in a rapid decrease in the leaf osmotic potential. The N, protein and proline contents increased under drought, while the N protein/NKjeldahlratio decreased. Initially, total soluble sugars increased at both N‐levels but dropped back to the control level at high N‐availability under prolonged drought while remaining high in N‐deficient plants. Results indicate that potatoes have only a limited capacity of activeOAand that increasing sugar and proline concentrations are rather associated with the protection of cellular components. High N supply promoted the N protein/NKjeldahlratio at short‐term drought and enhanced proline accumulation. Significant genotypic differences were observed for all investigated traits.

Differential Response to Salt Stress Within and Among Iranian Melilotus Species

ABSTRACTThis paper explores the salt-tolerance response of Melilotus species, a forage legume, based on tolerance/susceptibility indices, leaf water relations, leaf/root ion concentrations and multivariate (factor and function discriminate) analyses. In a greenhouse experiment, salinity-susceptibility of 12 accessions of Melilotus (M. albus, M. indicus, M. officinalis) in addition, two controls (alfalfa and Persian clover) were evaluated at 0 mM, 100 mM, 200 mM, and 300 mM of sodium chloride (NaCl). The experiment was conducted in a split plot design with two replications. Stress tolerance score (STS) was calculated based on tolerance/susceptibility indices. Salt-tolerant accessions were identified. An extracted bi-plot based on factor analysis confirmed the results of tolerance/susceptibility indices. There were significant correlations between STS and multivariate statistics. Root potassium cation (K+) concentration was higher in Melilotus species than the control species in all the salinity treatments. STS, root K+ concentration, leaf turgidity, and leaf succulence characteristics can be used for screening salinity-tolerance in Melilotus accessions. In all treatments, M. officinalis, M. indicus, and M. albus were salinity-tolerant species in descending order.Abbreviations: Total biomass yield under control (Yp) and stress (Ys) mediums, geometric mean productivity (GMP), leaf area (LA), leaf tissue density (LTD), linear regression coefficient (b), mean productivity (MP), relative water content (RWC%), Succulence (S), specific leaf area (SLA), stress susceptibility index (SSI), stress tolerance index (STI), tolerance (TOL), water content at saturation (WCS), water saturation deficit (WSD), sodium chloride (NaCl), potassium cation (K+), sodium cation (Na+), analysis of variance (ANOVA), least significant difference (LSD), alfalfa control accession (CHA), Persian clover control accession (CHC), coefficient of variation (CV), statistics of factor (F) and discriminate function (D)

Great Plains Winter Wheat Varies for Root Length and Diameter under Drought Stress

Core Ideas Great Plains winter wheat genotypes differed for root traits in a greenhouse study.Total root length was negatively correlated with average root diameter under moisture stress.Root length deep in the profile was positively associated with leaf relative water content.Semi‐dwarfing alleles did not significantly affect any root system trait. Development of a deep, extensive root system is a drought adaptation mechanism that is beneficial for maintaining productivity under water scarcity in dryland cropping systems. To determine variation for root biomass, depth, length, and diameter and related physiological traits in winter wheat (Triticum aestivum L.), we conducted two greenhouse studies under drought stress. Study I evaluated 30 entries (cultivars and advanced lines) primarily from Colorado, and Study II included 30 entries from seven U.S. Great Plains states. Evaluations were conducted on pre‐flowering plants in 1 m by 10 cm plastic tubes under greenhouse conditions. Tubes were weighed daily, and aboveground biomass (ABM) and root sections were collected after a 3‐wk dry‐down treatment. Roots were washed, scanned, and digitally analyzed. The Colorado entries differed significantly (P &lt; 0.05) for estimated transpiration, ABM, average root diameter, total root length, and root length in most diameter classes. Great Plains entries differed significantly (P &lt; 0.05) for ABM, stomatal conductance, water use efficiency, total root length, and root length for several diameter classes. Total root length correlated positively (P &lt; 0.05) with leaf elongation rate and relative water content in Study I and negatively with average root diameter in Study II. There was no significant effect of the Rht‐B1b or Rht‐D1b alleles on root system growth of the Great Plains winter wheat germplasm. Variation in root traits can be exploited in breeding programs to develop plants with the best adapted root systems to withstand drought stress.