Reduced Plant Water Research Articles

Specific phytohormones levels in leaves and spikes of wheat explains the effects of elevated CO2 on drought stress at the flowering stage

This study aims to understand the combined impact of elevated CO2 and drought stress at flowering stage to explain the adaptation of bread wheat to future climate change scenarios. Four wheat genotypes with 24 replications of each were grown in two different greenhouses, maintaining 400 (ambient) and 800 (elevated) ppm levels of CO2. Irrigation was withheld at flowering to impose drought to 10 replications while 10 were allowed to grow normally. Daily water consumption was recorded until the pot-water of drought plants reached 10 % of the well-watered ones. This study was aided by the measurement of ecophysiology, phytohormones, and yield-related traits. In comparison to normal CO2, plants consumed the pot water quickly under elevated CO2. Further, the threshold value of the fraction of transpirable soil water, at which the relative transpiration is diverging from 1 was different at the two levels of CO2, and among genotypes. Drought significantly reduced plant water relations, gas exchange parameters, grain yield, and yield-related traits but enhanced osmotic adjustment, kernel abortion, and most of the phytohormones in leaves and spikes. Elevated CO2 though increased gas exchange parameters significantly under well-watered conditions but these parameters were significantly reduced under combined effect with drought and resultantly, lower yield-related traits were recorded. Moreover, we also identified a strong positive association between leaf trans-zeatin and a strong negative association of leaf and spike ABA and ACC with grain yield indicating that maintenance of a higher level of leaf trans-zeatin or lower levels of ABA and ACC can help plants to adapt better to the combination of elevated CO2 and drought.

Effect of Anti-Transpiration and Potassium on Water Use Efficiency and Water Consumption under Water Stress Conditions to Climate Change Resistance

Climate change impact serious threats to global food security due to changes in water requirements resulting from the variation and instability of the spatial and temporal distribution of rainfall and the lack of water availability. Therefore, our research aims to use anti-transpiration agents that reduce plant water consumption, thus providing adequate amounts of water for agriculture in arid areas. A field experiment was conducted under water stress conditions during the winter seasons 2022-2023 and 2023-2024. The study included three levels of water stress, which are depletion of 40, 55 and 70% of the available water at a depth of 20 cm for the first three irrigations and a depth of 30 cm for the remaining irrigations and for the three treatments in succession. Anti-transpiration was added from different sources, which are kaolin, paraffin wax, silicon and potassium, in addition to the comparison treatment (spraying with water only). The results showed significant differences between the depletion treatments, as the 40% depletion treatment of the available water was significantly superior in most of the characteristics of the crop and its components, as the amount of increase in the grain yield was 62.24 and 64.22% for the two seasons in succession, compared to the 70% depletion treatment of the available water, which gave the lowest averages for all the studied characteristics. The irrigation treatment after depleting 40% of the available water was characterized by the best water use efficiency of 1.60 and 1.44 kg m-3 for the two seasons respectively, compared to the treatment of depleting 70% of the available water, which gave the lowest water use efficiency of 1.14 and 1.02 kg m-3 for the two seasons respectively. Spraying with anti-transpiration and potassium led to a significant increase in the yield and all its components compared to the comparison treatment (spraying with water only), which gave the lowest averages for all the studied traits, as spraying with potassium and kaolin gave a significant increase in most of the studied traits. Also, anti-transpiration and potassium, represented by potassium and kaolin, had a significant effect on water use efficiency, as the increase amount when spraying with potassium was 45.87 and 46.93% for the two seasons respectively compared to the comparison treatment (spraying with water only). As for the actual water consumption, we find an increase in the values ​​of water consumption and the number of irrigations in the comparison treatment (spraying with water only) compared to the anti-transpiration and potassium treatments, as the anti-transpiration and potassium provided water at a depth of 550, 414 and 405 m3 ha-1 for the first season and 615, 375 and 393 m3 ha-1 for the second season for the depletion treatments of 40, 55 and 70% of the available water, respectively, compared to the comparison treatment (spraying with water only). This increase is not small when applied to large areas and providing additional agricultural areas that can be invested. These findings suggest that targeted use of these treatments can effectively mitigate the effects of water stress, improving wheat production and resource efficiency in water-limited environments.

Alleviation of Drought Stress in Soybean [Glycine max (L.) Merril] by Foliar Application of Thiourea on Productivity and Profitability under Rainfed Condition

Background: In changing climatic scenario, plants often face periods of soil and atmospheric water deficits because of scarcity of water availability and deteriorating quality across the globe. Drought stress is the one of the major abiotic factors that reduce plant water status, obstructs photosynthesis, brings oxidative stress hindering soybean productivity. In view of this, bioregulators (thiourea) are innovative agricultural technique used to protect plants, minimizing the adverse effects caused by environmental stress. Therefore, an alternative to improve crop yield under rainfed condition by application of bioregulators like thiourea and suitable varieties are important in order to mitigate stress in soybean production. Methods: The field experiments were conducted in Factorial RBD with three replications. To know the impact of foliar spray of thiourea on growth, physiological parameters, yield parameters, yield and economics of two soybean varieties were carried out during kharif 2020, 2021 and 2022. Result: Long term results showed that, by using MACS 1188 variety of soybean and foliar spray of thiourea at 500 ppm and 750 ppm during the 25 and 55 DAS is a commendatory option and most remunerative for farmers to improve the productivity and profitability of soybean in Northern Transition Zone of Karnataka.

Reducing stomatal density by expression of a synthetic epidermal patterning factor increases leaf intrinsic water use efficiency and reduces plant water use in a C4 crop.

Enhancing crop water use efficiency (WUE) is a key target trait for climatic resilience and expanding cultivation on marginal lands. Engineering lower stomatal density to reduce stomatal conductance (gs) has improved WUE in multiple C3 crop species. However, reducing gs in C3 species often reduces photosynthetic carbon gain. A different response is expected in C4 plants because they possess specialized anatomy and biochemistry which concentrates CO2 at the site of fixation. This modifies the relationship of photosynthesis (AN) with intracellular CO2 concentration (ci), such that photosynthesis is CO2 saturated and reductions in gs are unlikely to limit AN. To test this hypothesis, genetic strategies were investigated to reduce stomatal density in the C4 crop sorghum. Constitutive expression of a synthetic epidermal patterning factor (EPF) transgenic allele in sorghum led to reduced stomatal densities, reduced gs, reduced plant water use, and avoidance of stress during a period of water deprivation. In addition, moderate reduction in stomatal density did not increase stomatal limitation to AN. However, these positive outcomes were associated with negative pleiotropic effects on reproductive development and photosynthetic capacity. Avoiding pleiotropy by targeting expression of the transgene to specific tissues could provide a pathway to improved agronomic outcomes.

Performance of Convergent Breeding Wheat (Triticum aestivum L.) Lines in the Lowlands

The development of tropical wheat in Indonesia is currently confined to the availability of wheat’s optimal environments in the highlands. Wheat competes with major highland crops, such as vegetables, which also have high economic values. Despite this, the demand for wheat in Indonesia remains high, whether in the form of wheat flour, wheat meal, or oats. Wheat breeders are actively working to create various crossbreeds so that wheat can adapt and perform effectively in lowland areas. The convergent breeding method is one of the strategies employed to produce genotypes with superior performance. Convergent breeding enhances genetic diversity by incorporating superior traits from all parent plants. The breeding results expedite the emergence of genetic combinations between selected parents. This method involves combining several parent varieties with various traits, with the hope that their offspring will inherit all the characteristics of the crossed parents. Our study with wheat convergent breeding has reached the F6 generation, and in this current study we evaluated the performance of each observed trait in different environments, with the goal of determining the levels of homogeneity and homozygosity. The study utilized a randomized complete block design with three replications, and the crops were planted in various locations. The planting locations selected were those that are >1000 m above sea level (asl), and at a lowland of ± 250 m asl. Wheat performance based on stomatal characteristics showed a reduction in the lowland, which indicates a response to climatic conditions in a particular environment. The higher the environmental temperatures, the smaller the stomatal size, which reduces plant water loss. Noteworthy findings include the tallest plant in CBF-6. CAMN23(265), the highest number of tillers in CBF-6. CAMN233 and CBF-6.CAMN8(4), the largest flag leaf area in CBF-7.CAMN60, and the highest 100-seed weight, as well as overall yield in CBF-7.CAMN119. An analysis of the lowland sensitivity index identified ten moderate genotypes that could potentially adapt well and achieve optimal yields.

Multi-trait efficiency and interactivity of bacterial consortia used to enhance plant performance under water stress conditions

Water stress is a major limiting factor for agricultural production under current and projected climate change scenarios. As a sustainable strategy, plant growth-promoting bacterial consortia have been used to reduce plant water stress. However, few studies have examined the effects of stress on multi-trait efficiency and interactivity of bacterial species. In this study, we used several in-vitro experiments, plant assays and greenhouse trials to investigate the effects of stress and bacterial consortia on 1-aminocyclopropane-1-carboxylic acid deaminase (ACCD) activities, indole-3-acetic acid (IAA) production and plant growth-promoting traits (Phosphate-solubilization, starch hydrolysis, siderophores and ammonium production). We further assessed biofilm formation and the chemotactic behaviour in response to ACC. A total of fifteen ACCD rhizobacteria with multiple growth-promoting traits from the dominant plant species from the hyperseasonal Aripo Savannas were screened in this study. Five of the isolates were further analyzed based on their ACCD activities and were tested in single and dual consortium to assess their abilities in promoting growth under simulated drought stress (−0.35 MPa) and chemically induced ACC conditions (0.03 mM). Our findings showed that bacteria which produce high concentrations of IAA affected the isolates’ ability to promote growth under stress, irrespective of microbial combination with ACCD activity above the minimal threshold of 20 nmol α-ketobutyrate mg−1 h−1. Biofilm production with co-culture interaction varied greatly across treatments, however, the general trend showed an increase in biofilm under stress induce conditions. The best performing co-culture, UWIGT-83 and UWIGT-120 (Burkholderia sp.) showed enhanced growth in germination assays and in greenhouse trials with Capsicum chinense (Moruga red hot peppers) under drought stress, when compared to non-inoculated treatments. The findings highlight the importance of testing interactivity of bacterial species with multiple growth promoting traits under stress conditions; and proposed the use of ACC growth media as a novel biofilm screening method for selecting potential stress plant growth-promoting bacteria. Better screening strategies for appropriate plant growth-promoting bacteria may narrow the inconsistency observed between laboratory and field trials.

Assessing the impact of deficit irrigation strategies on agronomic and productive parameters of Menara olive cultivar: implications for operational water management

The olive tree is an iconic tree in the Mediterranean region, traditionally cultivated under rainfed conditions; however, olive cultivars are also found outside the Mediterranean region and are widely used for oil and olive production. However, with the increasing aridity and global changes, olive agroecosystems are facing sustainability challenges. This study aims to evaluate the effect of two deficit irrigation strategies on the agronomic and productive parameters of the Menara, olive cultivar as a tool for operational irrigation water management. For this purpose, an experiment was conducted on an olive orchard for two consecutive years (2021 and 2022), comparing four regulated deficit irrigation (RDI) treatments and two sustained deficit irrigation (SDI) treatments, with fully irrigated trees. The results showed that moderate and controlled water stress under RDI did not significantly affect the yield of the Menara olive cultivar. In addition, by reducing plant water requirement by 20% during sensitive periods and by 40% during normal periods, under RDI, it is possible to save between 25% and 30% of irrigation water and to increase water productivity by 5%–20% with a slight decrease in fruit yield ranging between 10% and 15%. However, the trees subjected to the sustained deficit irrigation strategy exhibited a reduced capacity for shoot growth compared to those under RDI and fully irrigated conditions. Our findings showed that water deprivation during sensitive periods reduced phenological traits and slowed down shoot growth. Furthermore, the water status of the trees was reflected in fruit volume, as a decrease in water supply resulted in a corresponding reduction in fruit volume. Although the study provides important insights into water management strategies for olive cultivation, the short observation period does not allow for long-term plant adaptation evaluation and productivity beyond 2 years. Therefore, it is recommended that future studies extend the observation period to better understand plant adaptation to irrigation regimes.

Changes in root hydraulic conductivity in wheat (Triticum aestivum L.) in response to salt stress and day/night can best be explained through altered activity of aquaporins.

Salt stress reduces plant water flow during day and night. It is not known to which extent root hydraulic properties change in parallel. To test this idea, hydroponically grown wheat plants were grown at four levels of salt stress (50, 100, 150 and 200 mM NaCl) for 5-8d before harvest (d14-18) and subjected to a range of analyses to determine diurnal changes in hydraulic conductivity (Lp) at cell, root and plant level. Cell pressure probe analyses showed that the Lp of cortex cells was differentially affected by salt stress during day and night, and that the response to salt stress differed between the main axis of roots and lateral roots. The Aquaporin (AQP) inhibitor H2 O2 reduced Lp to a common, across treatments, level as observed in salt-stressed plants during the night. Analyses of transpiring plants and exuding root systems provided values of root Lp which were in the same range as values modeled based on cell-Lp. The results can best be explained through a change in root Lp in response to salt stress and day/night, which results from an altered activity of AQPs. qPCR gene expression analyses point to possible candidate AQP isoforms.

Bark Beetle Effects on Fire Regimes Depend on Underlying Fuel Modifications in Semiarid Systems

AbstractAlthough natural disturbances such as wildfire, extreme weather events, and insect outbreaks play a key role in structuring ecosystems and watersheds worldwide, climate change has intensified many disturbance regimes, which can have compounding negative effects on ecosystem processes and services. Recent studies have highlighted the need to understand whether wildfire increases or decreases after large‐scale beetle outbreaks. However, observational studies have produced mixed results. To address this, we applied a coupled ecohydrologic‐fire regime‐beetle effects model (RHESSys‐WMFire‐Beetle) in a semiarid watershed in the western US. We found that in the red phase (0–5 years post‐outbreak), surface fire extent, burn probability, and surface and crown fire severity all decreased. In the gray phase (6–15 years post‐outbreak), both surface fire extent and surface and crown fire severity increased with increasing mortality. However, fire probability reached a plateau during high mortality levels (>50% in terms of carbon removed). In the old phase (one to several decades post‐outbreak), fire extent and severity still increased in all mortality levels. However, fire probability increased during low to medium mortality (≤50%) but decreased during high mortality levels (>50%). Wildfire responses also depended on the fire regime. In fuel‐limited locations, fire probability increased with increasing fuel loads, whereas in fuel‐abundant (flammability‐limited) systems, fire probability decreased due to decreases in fuel aridity from reduced plant water demand. This modeling framework can improve our understanding of the mechanisms driving wildfire responses and aid managers in predicting when and where fire hazards will increase.

The Effect of Biochar Amendment on Physiological and Biochemical Properties and Nutrient Content of Lettuce in Saline Water Irrigation Conditions

Salinity often increases osmotic stress, reducing plant water uptake and inhibiting the absorption of nutrients and minerals. This imbalance situation causes physiological, biochemical disorders, and nutrient deficiencies in plants. In this study, the effects of biochar application on the physiological properties, nutrient contents and antioxidant enzyme activities of lettuce were investigated under saline irrigation water conditions. For this purpose, four different biochar doses and different irrigation water salinity levels were applied to the lettuce plant. In the study, biochar application under salt stress conditions decreased the Na, Fe, Zn content and antioxidant enzyme activity of the plant. Leaf relative water content, chlorophyll content (SPAD) and some nutrients (Ca, K, Mg, P, Cu and Mn) also increased. Therefore, biochar applied under salt irrigated water conditions offers good potential to reduce the severity of plant exposure to salinity stress. In addition, the biochar amendment helped the plant uptake of nutrients.

Inclusion of a cold hardening scheme to represent frost tolerance is essential to model realistic plant hydraulics in the Arctic–boreal zone in CLM5.0-FATES-Hydro

Abstract. As temperatures decrease in autumn, vegetation of temperate and boreal ecosystems increases its tolerance to freezing. This process, known as hardening, results in a set of physiological changes at the molecular level that initiate modifications of cell membrane composition and the synthesis of anti-freeze proteins. Together with the freezing of extracellular water, anti-freeze proteins reduce plant water potentials and xylem conductivity. To represent the responses of vegetation to climate change, land surface schemes increasingly employ “hydrodynamic” models that represent the explicit fluxes of water from soil and through plants. The functioning of such schemes under frozen soil conditions, however, is poorly understood. Nonetheless, hydraulic processes are of major importance in the dynamics of these systems, which can suffer from, e.g., winter “frost drought” events. In this study, we implement a scheme that represents hardening into CLM5.0-FATES-Hydro. FATES-Hydro is a plant hydrodynamics module in FATES, a cohort model of vegetation physiology, growth, and dynamics hosted in CLM5.0. We find that, in frozen systems, it is necessary to introduce reductions in plant water loss associated with hardening to prevent winter desiccation. This work makes it possible to use CLM5.0-FATES-Hydro to model realistic impacts from frost droughts on vegetation growth and photosynthesis, leading to more reliable projections of how northern ecosystems respond to climate change.

Physiological traits and response strategies of four subtropical tree species exposed to drought

World-wide, forests are experiencing drought-induced mortality. However, physiological adaptation to drought is highly variable, which may lead to differential mortality patterns and alter community structure. In this study, saplings of four common tree species ( Ormosia pinnata , Dalbergia odorifera , Castanopsis fissa and Michelia macclurei ) grown in subtropical plantations in southern China were subjected to average rainfall and three drought treatments, consisting of low (25% rainfall reduction), moderate (50% rainfall reduction) and high (75% rainfall reduction) drought. To investigate their drought response strategies and select tree species with higher drought tolerance, we examined plant traits, including tree growth, stomatal regulation, water relations, carbon dynamics and morphology, that might contribute to drought tolerance. We found that O. pinnata adapted to drought by decreasing turgor loss point (TLP) and increasing leaf dry matter content and leaf mass per area (LMA). D. odorifera exhibited low leaf minimum conductance and high LMA as the key drought traits to reduce water loss. C. fissa was slowest to initiate stomatal closure but completed stomatal closure more rapidly than the other species. Drought reduced light-saturated photosynthetic rates (A sat ) for O. pinnata , D. odorifera and C. fissa primarily due to declining stomatal conductance (g s ), with lesser limitations due to the biochemical capacity of Rubisco carboxylation (V cmax ) and electron transport (J max ). M. macclurei was the first species to close stomata. Drought did not affect A sat for M. macclurei due to stable photosynthetic biochemical processes; however, V cmax regulation of A sat increased with drought intensity. There was trait variation in the capacity of study trees to tolerate drought, with M. macclurei exhibiting the highest capacity to tolerate drought due to key stomatal (earlier stomatal closure) and hydraulic (lower TLP) traits reducing plant water loss with progressive drought stress. • Selecting species with morphological and physiological traits that confer high drought tolerance and resistance will be critical for designing and managing plantations. • M. macclurei might be the best adapted plantation tree for growth in future drier climates. • M. macclurei exhibited high drought avoidance and resistance, and maintained photosynthesis.

Plant water status, plant growth, and fruit yield in bell pepper (Capsicum annum L.) under shade nets

Shade nettings can be an effective technology for producing bell pepper under warm conditions. The physiological mechanisms through which shade nets improve plant growth and fruit yield are still not fully understood. The objectives were to determine the effects of shade level on plant and soil water status, plant growth and fruit yield of ‘Aristotle’ bell pepper. Trials were conducted in the spring/summer of 2017 and 2018 in Tifton, GA, following a randomized complete block design with five shade levels [0% (open field), 30%, 47%, 63%, and 80%]. Photosynthetic photon flux rate (PPFR) and leaf temperature decreased while soil water content and leaf water potential increased with shade level, indicating reduced plant water use due to reduced evaporative demand under shaded conditions. Increased shade levels resulted in enhanced plant growth in part because of improved plant water status. Total fruit yield and number of sunscalded fruit diminished with increasing shade level, while marketable yield was maximal at 30% shade. The incidences of soil-borne diseases [Phytophthora blight (Phytophthora capsici) and southern blight (Sclerotium rolfsii)] decreased with increasing shade levels. Overall, a shade level of 30% was found to be optimal and allowed production of maximal fruit yield through improving water availability (plant and soil water) and minimizing abiotic (drought, light, temperature) and biotic (pathogens) stresses.

Investigating root architectural differences in lines of Arabidopsis thaliana. L. with altered stomatal density using high resolution X-Ray synchrotron imaging

PurposeFreshwater is an increasingly scarce natural resource, essential for agricultural production. As plants consume 70% of the world’s freshwater, a reduction in their water use would greatly reduce global water scarcity. Plants with improved Water Use Efficiency (WUE) such as those with altered expression of the Epidermal Patterning Factor (EPF) family of genes regulating stomatal density, could help reduce plant water footprint. Little however, is known about how this modification in Arabidopsis thaliana. L. affects root architectural development in soil, thus we aim to improve our understanding of root growth when stomatal density is altered.MethodsWe used X-Ray synchrotron and neutron imaging to measure in three dimensions, the root system architecture (RSA) of Arabidopsis thaliana. L. plants of three different genotypes, namely that of the wild type Columbia (Col 0) and two different EPF mutants, EPF2OE and epf2-1 (which show reduced and increased stomatal density, respectively). We also used the total biomass and carbon isotope discrimination (Δ) methods to determine how WUE varies in these genotypes when grown in a sandy loam soil under controlled conditions.ResultsOur results confirm that the EPF2OE line had superior WUE as compared to the wild type using both the Δ and total biomass method. The epf2-1 mutant, on the other hand, had significantly reduced WUE using the Δ but not with the biomass method. In terms of root growth, the RSAs of the different genotypes had no significant difference between each other. There was also no significant difference in rhizosphere porosity around their roots as compared to bulk soil for all genotypes.ConclusionOur results indicate that the EPF mutation altering stomatal density in Arabidopsis thaliana. L. plants did not have an adverse effect on root characteristics thus their wide adoption to reduce the global freshwater footprint is unlikely to compromise their soil foraging ability.

Understanding and Exploiting Transpiration Response to Vapor Pressure Deficit for Water Limited Environments.

More frequent droughts and an increased pressure on water resources, combined with social licence to operate, will inevitably decrease water resources available for fully irrigated cotton production. Therefore, the long-term future of the cotton industry will require more drought tolerant varieties that can perform well when grown in rainfed cropping regions often exposed to intermittent drought. A trait that limits transpiration (TRLim) under an increased vapour pressure deficit (VPD) may increase crop yield in drier atmospheric conditions and potentially conserve soil water to support crop growth later in the growing season. However, this trait has not been tested or identified in cotton production systems. This study tested the hypotheses that (1) genetic variability to the TRLim VPD trait exists amongst 10 genotypes in the Australian cotton breeding programme; (2) genotypes with a TRLim VPD trait use less water in high VPD environments and (3) variation in yield responses of cotton genotypes is linked with the VPD environment and water availability during the peak flowering period. This study combined glasshouse and field experiments to assess plant transpiration and crop yield responses of predominantly locally bred cotton genotypes to a range of atmospheric VPD under Australian climatic conditions. Results indicated that genetic variation to the limiting transpiration VPD trait exists within cotton genotypes in the Australian breeding programme, with five genotypes identified as expressing the TRLim VPD trait. A modelling study suggests that this trait may not necessarily result in overall reduced plant water use due to greater transpiration rates at lower VPD environments negating the water conservation in high VPD environments. However, our study showed that the yield response of cotton genotypes is linked with both VPD environment and water availability during the peak flowering period. Yield performance of the TRLim genotype was improved at some high VPD environments but is unlikely to out-perform a genotype with a lower yield potential. Improved understanding of integrated plant- and crop-level genotypic responses to the VPD environments will enhance germplasm development to benefit cotton production in both rainfed and semi-irrigated cotton systems, thereby meeting the agricultural challenges of the twenty-first Century.

Trehalose increases tomato drought tolerance, induces defenses, and increases resistance to bacterial wilt disease.

Ralstonia solanacearum causes bacterial wilt disease, leading to severe crop losses. Xylem sap from R. solanacearum-infected tomato is enriched in the disaccharide trehalose. Water-stressed plants also accumulate trehalose, which increases drought tolerance via abscisic acid (ABA) signaling. Because R. solanacearum-infected plants suffer reduced water flow, we hypothesized that bacterial wilt physiologically mimics drought stress, which trehalose could mitigate. We found that R. solanacearum-infected plants differentially expressed drought-associated genes, including those involved in ABA and trehalose metabolism, and had more ABA in xylem sap. Consistent with this, treating tomato roots with ABA reduced both stomatal conductance and stem colonization by R. solanacearum. Treating roots with trehalose increased xylem sap ABA and reduced plant water use by lowering stomatal conductance and temporarily improving water use efficiency. Trehalose treatment also upregulated expression of salicylic acid (SA)-dependent tomato defense genes; increased xylem sap levels of SA and other antimicrobial compounds; and increased bacterial wilt resistance of SA-insensitive NahG tomato plants. Additionally, trehalose treatment increased xylem concentrations of jasmonic acid and related oxylipins. Finally, trehalose-treated plants were substantially more resistant to bacterial wilt disease. Together, these data show that exogenous trehalose reduced both water stress and bacterial wilt disease and triggered systemic disease resistance, possibly through a Damage Associated Molecular Pattern (DAMP) response pathway. This suite of responses revealed unexpected linkages between plant responses to biotic and abiotic stress and suggested that R. solanacearum-infected plants increase trehalose to improve water use efficiency and increase wilt disease resistance. The pathogen may degrade trehalose to counter these efforts. Together, these results suggest that treating tomatoes with exogenous trehalose could be a practical strategy for bacterial wilt management.

Supplemental Irrigation with Brackish Water Improves Carbon Assimilation and Water Use Efficiency in Maize under Tropical Dryland Conditions

Dry spells in rainfed agriculture lead to a significant reduction in crop yield or to total loss. Supplemental irrigation (SI) with brackish water can reduce the negative impacts of dry spells on net CO2 assimilation in rainfed farming in semi-arid tropical regions and maintain crop productivity. Thus, the objective of this study was to evaluate the net carbon assimilation rates, indexes for water use efficiency, and indicators of salt and water stress in maize plants under different water scenarios, with and without supplemental irrigation with brackish water. The experiment followed a randomized block design in a split-plot design with four replications. The main plots simulated four water scenarios found in the Brazilian semi-arid region (Rainy, Normal, Drought, and Severe Drought), while the subplots were with or without supplemental irrigation using brackish water with an electrical conductivity of 4.5 dS m−1. The dry spells reduced the photosynthetic capacity of maize, especially under the Drought (70% reduction) and Severe Drought scenarios (79% reduction), due to stomatal and nonstomatal effects. Supplemental irrigation with brackish water reduced plant water stress, averted the excessive accumulation of salts in the soil and sodium in the leaves, and improved CO2 assimilation rates. The supplemental irrigation with brackish water also promoted an increase in the physical water productivity, reaching values 1.34, 1.91, and 3.03 times higher than treatment without SI for Normal, Drought, and Severe Drought scenarios, respectively. Thus, the use of brackish water represents an important strategy that can be employed in biosaline agriculture for tropical semi-arid regions, which are increasingly impacted by water shortage. Future studies are required to evaluate this strategy in other important crop systems under nonsimulated conditions, as well as the long-term effects of salts on different soil types in this region.

Unexpected Responses of Bean Leaf Size to Elevated CO2.

CO2 is currently a growth-limiting resource for plants with C3 metabolism, and elevated CO2 also often reduces stomatal conductance, reducing plant water stress. Increased photosynthesis and improved water status might be expected to result in increased leaf size. It is therefore unexpected that leaf size is in some cases reduced in plants grown at elevated CO2, and also unexpected that elevated CO2 applied only during darkness can increase leaf size. These experiments compared leaf size responses to day and/or night elevated CO2 in six cultivars of Phaseolus vulgaris grown with either constant or varying temperature in controlled environment chambers. Diverse responses of leaf size to elevated CO2 were found among the cultivars, including increased leaf size with elevated CO2 applied only during darkness in some cultivars and temperature regimes. However, leaf size responses to elevated CO2 and cultivar differences in response were unrelated to differences in leaf water potential or turgor pressure.

Reduced plant water use can explain higher soil moisture in organic compared to conventional farming systems

Conventional high-input farming systems in Europe are often regarded as unsustainable with severe environmental impacts on biodiversity, soils, water and climate. Low-input farming approaches, such as organic farming, have been proposed to reduce environmental impacts while further improving soil properties such as soil organic matter content and aggregate stability. Whether these changes also influence ecohydrological properties and improve the water relations of organically grown crops remains unclear. In this study we assessed the long-term effects of conventional and organic farming systems on the water relations of soils and crops in the “DOK” (bio-Dynamic, bio-Organic & ‘Konventionell’ = conventional) trial. In particular, we tested if organic and conventional farming lead to marked differences in soil moisture, soil water evaporation, as well as root water uptake depth and stomatal conductance of winter wheat and soybean during the growing seasons 2017 and 2018. Stable isotope analyses and ecophysiological measurements revealed that organic compared to conventional farming did not affect soil water evaporation or root water uptake depths. Instead, we found higher soil moisture in the rooting zone and reduced stomatal conductance (gs) in organically grown wheat. Treatment effects on soil moisture and gs of soybean were smaller but showed similar tendencies as observed in wheat. Also, leaf area, and grain and straw yield of wheat decreased under organic farming while yields of soybean were not affected by the treatments. Based on our data we suggest that reduced plant water use observed under organically managed farming lead to the observed higher soil moisture in organically compared to conventionally managed farming systems in the DOK trial. These results suggest advantages of organic farming regarding agronomic water use as well as for the resistance of farming systems to current or future drought scenarios.

The Effect of Applied Salinity and Water Stress on Chemical Suppression of Phytophthora ramorum from Soilborne Inoculum in Rhododendron.

A serious concern for nurseries is the potential for Phytophthora ramorum and other Phytophthora species to colonize roots without inducing aboveground symptoms in plants that then serve as cryptic reservoirs of inoculum. Episodic abiotic stresses that reduce plant water potential can compromise the host resistance to trigger disease development from root and crown infections during many Phytophthora-plant interactions. We conducted a series of experiments with root-inoculated Rhododendron plants in a potting soil mix to assess the influence of excess salt or water deficit on ramorum blight development and the potential for these abiotic stresses to affect the efficacy of oomycete-suppressive chemical soil treatments. During growth chamber trials, P. ramorum colonized roots of both nonsalt-treated and salt-treated plants. However, salt treatment offset the benefit realized from soil treatment with mefanoxam (Subdue Maxx) and mandipropamid (Micora), as evidenced by the enhanced pathogen colonization of roots. A 3-week episode of water stress imposed after chemical treatment but before inoculation eliminated protection against P. ramorum root colonization conferred by fosetyl-Al (Aliette). At an outdoor experimental nursery, foliar symptoms were apparent in 23% of root-inoculated plants during two trials and absent during one trial. However, the majority of inoculated plants in all trials had colonized roots with little or no aboveground symptoms. A single application of Subdue Maxx or Aliette reduced root colonization by P. ramorum in Rhododendron plants. Although salt stress did not enhance ramorum blight symptom expression at the nursery, salt partially offset protection from P. ramorum root colonization obtained by Subdue Maxx.