Decrease In Transpiration Rate Research Articles

Physiological and growth responses of Lycium barbarum seedlings to water and salt stresses

Rational exploitation and utilization of brackish water resources is the basis of sustainable agricultural development in the oasis regions of arid inland basin. As a drought-and-salt-tolerant economic crop, irrigation management at seedling stage is particularly important for the fruit yield in Lycium barbarum adulthood. The effects of three irrigation levels (the lower limits of irrigation were 80 % (full irrigation), 70 %, and 60 % of field capacity) and two salinity levels in irrigation water (1.7 (fresh water) and 5.0 dS/m) on physiology and growth of Lycium barbarum seedlings were studied through pot experiments. The results showed that water deficit treatment promoted aboveground plant growth and water use efficiency, but decreased transpiration rate of Lycium barbarum seedlings. Compared with full irrigation, the averaged leaf chlorophyll content (SPAD), base stem diameter, branch diameter, and water use efficiency of Lycium barbarum seedlings under deficit irrigation treatments were increased by 4.6 % – 6.6 %, 15.1 % – 55.5 %, 12.8 % – 41.0 %, and 22.3 % – 23.9 %, respectively, while the transpiration rate was decreased by 6.5 % – 16.1 %. Soil water content under brackish water irrigation was generally slightly higher than that under freshwater irrigation, but its soil salinity was about 5.0 times higher than that under freshwater irrigation. Compared with freshwater irrigation, brackish water irrigation decreased root biomass by 6.7 % – 9.0 % and transpiration rate by 2.5 % – 10.5 %, and increased water use efficiency by 1.9 % – 24.8 %, and meanwhile it also promoted the growth of base stem (11.4 % – 32.4 %), branch (6.4 % – 18.9 %) and leaf aera (2.2 % – 6.8 %). The lower limit of irrigation and the salinity in irrigation water imposed significant interactive effects on photosynthesis, stem and branch growth, and crop water consumption of Lycium barbarum seedlings. The analysis results of structural equation model showed that the lower limit of irrigation mainly affected water use efficiency of Lycium barbarum seedlings, while the salinity in irrigation water mainly did its root biomass. The lower limit of irrigation with 70 % field capacity may be a preferred scheme of brackish water irrigation for the planting of Lycium barbarum seedlings in arid oasis regions.

Unexpectedly, triple super phosphate fertilizer induces maize drought resilience

Phosphorus fertilizer is commonly applied to soils in crop production as diammonium phosphate (DAP). To decrease ammonium addition to the environment, triple super phosphate (TSP) is being considered as a DAP replacement. This study was undertaken to compare the response of maize plants to soil fertilization with TSP vs. DAP under well-watered conditions, under soil-drying conditions, and root hydraulic conductance. It was found for well-watered conditions in a controlled environment that there was no difference in plant growth between DAP to TSP treatments. In soil dry-down experiments, however, the initiation of the decrease in transpiration rate was unexpectedly quite different between DAP and TSP treatments. The soil water content threshold for initiation of decrease in transpiration rate with DAP treatment (average fraction transpirable soil water for two experiments = 0.285) was consistent with common observations, but the threshold associated with TSP treatment occurred at an unusually high soil water content (average fraction transpirable soil water for two experiments = 0.545). The higher threshold with TSP resulted in an extended period of soil water use, i.e. soil water conservation. Soil water conservation resulting from the TSP treatment was associated with a 27% greater shoot mass accumulation following a 4-wk re-watering period after the water-deficit treatment than measured with the DAP treatment. The high threshold for decrease in transpiration resulting from TSP was consistent with measured lower root hydraulic conductance as compared to DAP treatment. The unexpected discovery of TSP-induced initiation of transpiration rate decrease at high soil water content is consistent with greater crop drought resilience.

Differential eco-physiological performance to declining groundwater depth in Central Asian C3 and C4 shrubs in the Gurbantunggut Desert.

Resources in water-limited ecosystems are highly variable and unpredictable, and the maintenance of functional diversity among coexisting species is a crucial ecological strategy through which plants mitigate environmental stress. The comparison of differential eco-physiological responses among co-occurring plants in harsh environments could help provide deep insights into the coexistence mechanisms of competing species. Two coexisting desert shrubs with different photosynthetic pathways (Haloxylon ammodendron and Tamarix ramosissima) were selected in the Gurbantunggut Desert located in northwest China. This study detected variations in the water sources, photosynthetic parameters, stem water status, and non-structural carbohydrates of the two shrubs at three sites with different groundwater table depths during the growing seasons of 2015 and 2016 to identify distinct eco-physiological performances in coexisting plants with different functional types under fluctuating water conditions. The water sources of H. ammodendron shifted from soil water to groundwater, while T. ramosissima extracted water mainly from deep soil layers at both sites. Significant reductions in carbon assimilation and stomatal conductance in H. ammodendron with deeper groundwater table depth were detected during most drought periods, but no significant decreases in transpiration rate were detected with declining groundwater table depth. For T. ramosissima, all of these gas exchange parameters decreased with the progression of summer drought, and their relative reduction rates were larger compared with those of H. ammodendron. The stem water status of H. ammodendron deteriorated, and the relative reduction rates of water potential increased with deeper groundwater, whereas those of T. ramosissima did not differ with greater groundwater depth. These findings indicated that prolonged drought would intensify the impact of declining groundwater depth on the eco-physiology of both shrubs, but the extent to which the shrubs would respond differed. The two shrubs were segregated along the water-carbon balance continuum: the C3 shrub T. ramosissima maximized its carbon fixation at an enormous cost of water, while greater carbon fixation was achieved with far greater water economy for H. ammodendron. These results demonstrated that the two shrubs prioritized carbon gain and water loss differently when faced with limited water sources. These mechanisms might mitigate competitive stress and enable their coexistence.

Real-Time Dynamics of Water Transport in the Roots of Intact Maize Plants in Response to Water Stress: The Role of Aquaporins and the Contribution of Different Water Transport Pathways.

Using an original methodological and technical approach, we studied the real-time dynamics of radial water transfer in roots and transpiration rate in intact maize plants in response to water stress. It was shown that the response of maize plants to water stress, induced by 10% PEG 6000, was accompanied by changes in the intensity and redistribution of water transfer along different pathways of radial water transport in the roots. It was shown that during the first minutes of water stress impact, the intensity of transcellular and symplastic water transport in the roots decreased with a parallel short-term increase in the transpiration rate in leaves and, presumably, in apoplastic transport in roots. Further, after a decrease in transpiration rate, the intensity of transcellular and symplastic water transport was restored to approximately the initial values and was accompanied by parallel upregulation of some PIP aquaporin genes in roots and leaves, changes in aquaporin localization in root tissues, and changes in xylem sap pH. Under water stress conditions, cell-to-cell water transport in roots becomes dominant, and aquaporins contribute to the simultaneous regulation of water transport in roots and shoots under water stress.

Impact of root architecture and transpiration rate on drought tolerance in stay‐green sorghum

AbstractSorghum [Sorghum bicolor (L.) Moench] yield loss due to terminal drought stress is common in semiarid regions. Stay‐green is a drought adaptation trait, and a deeper understanding of stay‐green‐associated traits is necessary for sorghum breeding. We hypothesize that the stay‐green trait in sorghum may be associated with the root architecture and transpiration rate under drought stress. The objectives were to (i) identify the relationship among stay‐green‐associated traits, (ii) compare the root system architecture and transpiration rate of stay‐green (B35 and 296B) and senescent (BTx623 and R16) genotypes under drought stress, and (iii) quantify the impacts of reproductive stage drought stress on gas exchange and grain yield of stay‐green and senescent genotypes. A series of drought experiments were conducted with these genotypes. Under drought stress, the stay‐green genotypes had an increased total root length in the top 30–60 cm (18%) and 60–90 cm of soil (45%) than the senescent genotypes. In contrast, under progressive soil drying, stay‐green genotypes had a decreased transpiration rate (9%) than senescent genotypes by an early (∼1 h) partial closure of stomata under high vapor pressure deficit conditions. The increased seed yield (43%) in stay‐green genotypes is due to an increased photosynthetic rate (30%) and individual seed size (35%) than senescent genotypes. Overall, it is concluded that stay‐green phenotypes had two distinct drought adaptive mechanisms: (i) increased root length for increased soil exploration for water and (ii) an early decrease in the transpiration rate to conserve soil moisture. Identifying genomic markers for these traits would accelerate drought‐tolerant sorghum breeding.

Investigating high throughput phenotyping based morpho-physiological and biochemical adaptations of indian pennywort (Centella asiatica L. urban) in response to different irrigation regimes

Indian pennywort (Centella asiatica L. Urban; Apiaceae) is a herbaceous plant used as traditional medicine in several regions worldwide. An adequate supply of fresh water in accordance with crop requirements is an important tool for maintaining the productivity and quality of medicinal plants. The objective of this study was to find a suitable irrigation schedule for improving the morphological and physiological characteristics, and crop productivity of Indian pennywort using high-throughput phenotyping. Four treatments were considered based on irrigation schedules (100, 75, 50, and 25% of field capacity denoted by I100 [control], I75, I50, and I25, respectively). The number of leaves, plant perimeter, plant volume, and shoot dry weight were sustained in I75 irrigated plants, whereas adverse effects on plant growth parameters were observed when plants were subjected to I25 irrigation for 21 days. Leaf temperature (Tleaf) was also retained in I75 irrigated plants, when compared with control. An increase of 2.0 °C temperature was detected in the Tleaf of plants under I25 irrigation treatment when compared with control. The increase in Tleaf was attributed to a decreased transpiration rate (R2 = 0.93), leading to an elevated crop water stress index. Green reflectance and leaf greenness remained unchanged in plants under I75 irrigation, while significantly decreased under I50 and I25 irrigation. These decreases were attributed to declined leaf osmotic potential, increased non-photochemical quenching, and inhibition of net photosynthetic rate (Pn). The asiatic acid and total centellosides in the leaf tissues, and centellosides yield of plants under I75 irrigation were retained when compared with control, while these parameters were regulated to maximal when exposed to I50 irrigation. Based on the results, I75 irrigation treatment was identified as the optimum irrigation schedule for Indian pennywort in terms of sustained biomass and a stable total centellosides. However, further validation in the field trials at multiple locations and involving different crop rotations is recommended to confirm these findings.

Non-Invasive Micro-Test Technology and Reciprocal Grafting Provide Direct Evidence of Contrasting Na+ Transport Strategies between Cucurbita moschata and Cucurbita maxima

Cucurbita species are widely used as rootstocks for cucumber, watermelon, and other plants for the restriction of toxic Na+ transport from root to shoot. Previous studies have found distinct salt tolerance strategies between Cucurbita moschata and Cucurbita maxima; the former accumulates a large amount of Na+ in the root, while the latter accumulates Na+ in the shoot. To further study the mechanism of Na+ transport in plants, four reciprocal grafts were made between MB (C. moschata) and JHL (C. maxima), denoted as MB/MB, JHL/JHL, MB/JHL, and JHL/MB (scion/rootstock). The results showed that using MB as the rootstock effectively reduced the accumulation of Na+ in the scion. Conversely, JHL rootstock tended to transfer more Na+ to the scion. To clarify this phenomenon, the velocities of Na+ flows on the root surface, stem, and vein of grafting combinations were measured using non-invasive micro-test technology. Compared with the seedlings using JHL as rootstock, the grafted combination with MB as rootstock had a higher root Na+ efflux and lower Na+ fluxes in the stem and vein. qRT-PCR analyses revealed the critical roles of salt overly sensitive 1 and high-affinity potassium as components of the mechanism enabling Na+ exclusion from the root and Na+ unloading from the stem xylem. Compared with the seedlings using MB as rootstocks, the JHL-grafted plants showed more rapid stomatal closure and decreased transpiration rate in the first three hours after salt stress but maintained a higher level under prolonged salt treatment (120 h). The tissue tolerances of JHL and MB were assessed using the isolated leaves under NaCl to exclude the influence of the root and stem. The results showed that the salinity inflicted more serious damage to MB leaves than to JHL leaves. qRT-PCR analyses indicated that the intracellular Na+/H+ transporter in the leaf vein was involved in this process. All these findings indicated that C. moschata and C. maxima adopted different strategies for regulating Na+ transport, and grafting can be used as a tool to create more salt-tolerant plants.

Effects of Acetaminophen Contamination on 5-Methylcytosine Content in Zea mays and Plant Physiological Parameters

Zea mays L. plants were exposed to acetaminophen (APAP). Experiments were conducted in an experimental greenhouse with semi-controlled conditions. Experimental plants were grown in concentrations of APAP of 0, 200, 400, 600, 800, and 1000 mg L−1 for 14 days in an NFT hydroponic system. The impact of APAP contamination was observed on photosynthetic rate, water potential, proline content, and levels of 5-methylcytosine (5 mC%). The results showed that the selected parameters were influenced by different concentrations of APAP. High concentrations of APAP caused a decrease in transpiration rate, stomatal conductance, and water use efficiency. The water potential between the control and highest APAP concentration value increased by 388%. An upward trend of 5 mC% levels was observed, growing with APAP contamination. A 51% growth of 5 mC% was found between the control variant and the highest 1000 mg L−1 APAP contaminated variant. In most of the observed parameters, between 600 mg L−1 and 800 mg L−1 of APAP treatments, a turning point was shown with a noticeable increase in the stress in experimental plants according to the changes in the monitored parameters.

Seasonal changes in leaf water relations in regards to leaf drought tolerance in mature Cryptomeria japonica canopy trees

ABSTRACT Although seasonal differences in drought damage to Japanese cedar (Cryptomeria japonica D. Don) have been well studied, the mechanisms underlying these seasonal differences remain poorly understood. In this study, we measured seasonal changes in current-year shoot growth; leaf mass per area (LMA); water potential at turgor loss point (Ψtlp), predawn (Ψpre), and midday (Ψmid); osmotic potential (Ψs); maximum transpiration rates; and maximum stomatal conductance in a 43-year-old Japanese cedar stand, with particular focus on the relationship between the shoot growth period and seasonal variation in Ψtlp, and the turgor safety margin (Ψmid – Ψtlp) to identify the season in which these trees are most vulnerable to drought. Current-year shoot growth began in April, with high shoot growth continuing until August. Ψtlp varied significantly throughout the year and was particularly high during the shoot growth period. Increasing LMA and decreasing Ψs caused a reduction in Ψtlp from autumn to winter, and Ψmid dropped to approximately the level of Ψtlp during the summer due to high transpiration activity, and increased with decreasing transpiration rates during the winter. Thus, the turgor safety margin was smaller in the summer than in the winter. These results suggest that Japanese cedar is most vulnerable to drought in the summer due to high Ψtlp during the shoot growth period.

Assessing the risks of silver nanoparticle-concentrated matrix application in agricultural soil: Implications for plant and soil enzymes

The practice of reusing biosolids may be an effective strategy for addressing nutrient reuse and soil shortages. However, the accumulation of silver nanoparticles (AgNPs) in biosolids poses a major ecological hazard to organisms. In this study, we evaluated the effects of AgNPs on plant and soil enzymes in terrestrial ecosystems by exposing soybean Glycine max, as well as soil, to varying concentrations of AgNPs embedded either on the surface soil layer or throughout the soil matrix. We found that exposing the plants to 20 mg AgNPs/kg soil that was embedded throughout the soil matrix had a significant impact. Conversely, soil enzymes (dehydrogenase, urease, and fluorescein diacetate hydrolase) were affected by exposure to 20 and 80 mg AgNPs/kg of soil embedded on the surface soil layer or throughout the soil matrix at 20 mg AgNPs/kg soil. The toxic effects of AgNPs were induced by different receptor habitats.The presence of AgNPs in soil led to developmental retardation, inhibited root growth, reduced photosynthetic activity, and decreased transpiration rates in leaves. These plants also produced fewer fruits compared to soybean plants grown in regular soil without AgNPs. Moreover, most of the AgNPs soil groups demonstrated a decrease in soil enzyme activity in the surface soil; therefore, soil-capping patterns involving embedded stressors should be considered. These findings provide valuable insights that will contribute substantially to advancements in the field of biosolids for land applications.

Chitosan fabricated biogenic silver nanoparticles (Ch@BSNP) protectively modulate the defense mechanism of tomato during bacterial leaf spot (BLS) disease

Herein, the impact of chitosan fabricated biogenic silver nanoparticles (Ch@BSNP) has been evaluated for the protective management of bacterial leaf spot (BLS) disease in tomatoes caused by Xanthomonas campestris (NCIM5028). The Ch@BSNP originated by the Trichoderma viride (MTCC5661) derived extracellular compounds and subsequent chitosan hybridization. Spherical-shaped Ch@BSNP (30–35 nm) treated diseased plants were able to combat the biotic stress, as evidenced by the decreased elevated response of stress markers viz; anthocyanin (34.02%), proline (45.00%), flavonoids (20.26%), lipid peroxidation (10.00%), guaiacol peroxidase (36.58%), ascorbate peroxidase (41.50%), polyphenol oxidase (25.34%) and phenylalanine ammonia-lyase (2.10 fold) as compared to untreated diseased plants. Increased biochemical content specifically sugar (15.43%), phenolics (49.10%), chlorophyll, and carotenoids were measured in Ch@BSNP-treated diseased plants compared to untreated X. campestris-infested plants. The Ch@BSNP considerably reduced stress by increasing net photosynthetic rate and water use efficiency along with decreased transpiration rate and stomatal conductance in comparison to infected plants. Additionally, the expression of defense-regulatory genes viz; growth responsive (AUX, GH3, SAUR), early defense responsive (WRKYTF22, WRKY33, NOS1), defense responsive (PR1, NHO1, NPR1), hypersensitivity responsive (Pti, RbohD, OXI1) and stress hormones responsive (MYC2, JAR1, ERF1) were found to be upregulated in diseased plants while being significantly downregulated in Ch@BSNP-treated diseased plants. Furthermore, fruits obtained from pathogen-compromised plants treated with Ch@BSNP had higher levels of health-promoting compounds including lycopene and beta-carotene than infected plant fruits. This nano-enabled and environmentally safer crop protection strategy may encourage a sustainable agri-system towards the world's growing food demand and promote food security.

Insight of PBZ mediated drought amelioration in crop plants.

Water scarcity is a significant environmental limitation to plant productivity as drought-induced crop output losses are likely to outnumber losses from all other factors. In this context, triazole compounds have recently been discovered to act as plant growth regulators and multi-stress protectants such as heat, chilling, drought, waterlogging, heavy metals, etc. Paclobutrazol (PBZ) [(2RS, 3RS)-1-(4-chlorophenyl)- 4, 4-dimethyl-2-(1H-1, 2, 4-trizol-1-yl)-pentan-3-ol)] disrupts the isoprenoid pathway by blocking ent-kaurene synthesis, affecting gibberellic acid (GA) and abscisic acid (ABA) hormone levels. PBZ affects the level of ethylene and cytokinin by interfering with their biosynthesis pathways. Through a variety of physiological responses, PBZ improves plant survival under drought. Some of the documented responses include a decrease in transpiration rate (due to reduced leaf area), higher diffusive resistance, relieving reduction in water potential, greater relative water content, less water use, and increased antioxidant activity. We examined and discussed current findings as well as the prospective application of PBZ in regulating crop growth and ameliorating abiotic stresses in this review. Furthermore, the influence of PBZ on numerous biochemical, physiological, and molecular processes is thoroughly investigated, resulting in increased crop yield.

Ethanol-Mediated Novel Survival Strategy against Drought Stress in Plants.

Water scarcity is a serious agricultural problem causing significant losses to crop yield and product quality. The development of technologies to mitigate the damage caused by drought stress is essential for ensuring a sustainable food supply for the increasing global population. We herein report that the exogenous application of ethanol, an inexpensive and environmentally friendly chemical, significantly enhances drought tolerance in Arabidopsis thaliana, rice and wheat. The transcriptomic analyses of ethanol-treated plants revealed the upregulation of genes related to sucrose and starch metabolism, phenylpropanoids and glucosinolate biosynthesis, while metabolomic analysis showed an increased accumulation of sugars, glucosinolates and drought-tolerance-related amino acids. The phenotyping analysis indicated that drought-induced water loss was delayed in the ethanol-treated plants. Furthermore, ethanol treatment induced stomatal closure, resulting in decreased transpiration rate and increased leaf water contents under drought stress conditions. The ethanol treatment did not enhance drought tolerance in the mutant of ABI1, a negative regulator of abscisic acid (ABA) signaling in Arabidopsis, indicating that ABA signaling contributes to ethanol-mediated drought tolerance. The nuclear magnetic resonance analysis using 13C-labeled ethanol indicated that gluconeogenesis is involved in the accumulation of sugars. The ethanol treatment did not enhance the drought tolerance in the aldehyde dehydrogenase (aldh) triple mutant (aldh2b4/aldh2b7/aldh2c4). These results show that ABA signaling and acetic acid biosynthesis are involved in ethanol-mediated drought tolerance and that chemical priming through ethanol application regulates sugar accumulation and gluconeogenesis, leading to enhanced drought tolerance and sustained plant growth. These findings highlight a new survival strategy for increasing crop production under water-limited conditions.

PdEPFL6 reduces stomatal density to improve drought tolerance in poplar

Drought is an abiotic stress that affects growth, development and productivity of plants. Peptides play key roles in plant growth and development, acting in a similar manner as phytohormones. However, only a few peptides have been identified to play a role in abiotic stress tolerance of poplars. Here, we isolated an EPIDERMAL PATTERNING FACTOR (EPF) secreted Cys-rich small peptide PdEEPFL6 from NE19 [Populus nigra × (P. deltoides × P. nigra)] and explored its mechanism in plant response to drought stress. We found that PdEEPFL6 was greatly induced by dehydration treatment in poplar. To investigate its potential biological functions, PdEPFL6, was overexpressed in poplar 84 K (P. alba × P. glandulosa). PdEPFL6 overexpressing lines (OxPdEPFL6) significantly decreased stomatal density, resulting in the decrease of transpiration rate. OxPdEPFL6 lines maintained a higher photosynthetic rate and lower the water loss rate of leaves compared with the control, resulting in drought resistance increasing. Moreover, yeast two-hybrid and bimolecular fluorescence complementation assays revealed that PdEPFL6 interacted with PdTMM (receptor-like protein) and PdERECTA (receptor-like kinases). Overexpression of PdEPFL6 regulated the expression levels of MAPK-associated genes and significantly decreased the expressions of stomatal development-related transcription factors (PdSPCH and PdMUTE) under normal and drought conditions, leading to a decrease in stomatal density. Taken together, our findings show that PdEPFL6-PdERECTA/PdTMM module plays an essential role in stomatal development, the ligand-receptor pair plays an active role in regulating drought resistance by reducing stomatal density in poplar.

Phenotyping and Quantitative Trait Locus Analysis for the Limited Transpiration Trait in an Upper-Mid South Soybean Recombinant Inbred Line Population ("Jackson" × "KS4895"): High Throughput Aquaporin Inhibitor Screening.

Soybean is most often grown under rainfed conditions and negatively impacted by drought stress in the upper mid-south of the United States. Therefore, identification of drought-tolerance traits and their corresponding genetic components are required to minimize drought impacts on productivity. Limited transpiration (TRlim) under high vapor pressure deficit (VPD) is one trait that can help conserve soybean water-use during late-season drought. The main research objective was to evaluate a recombinant inbred line (RIL) population, from crossing two mid-south soybean lines (“Jackson” × “KS4895”), using a high-throughput technique with an aquaporin inhibitor, AgNO3, for the TRlim trait. A secondary objective was to undertake a genetic marker/quantitative trait locus (QTL) genetic analysis using the AgNO3 phenotyping results. A set of 122 soybean genotypes (120-RILs and parents) were grown in controlled environments (32/25-d/n °C). The transpiration rate (TR) responses of derooted soybean shoots before and after application of AgNO3 were measured under 37°C and >3.0 kPa VPD. Then, the decrease in transpiration rate (DTR) for each genotype was determined. Based on DTR rate, a diverse group (slow, moderate, and high wilting) of 26 RILs were selected and tested for the whole plant TRs under varying levels of VPD (0.0–4.0 kPa) at 32 and 37°C. The phenotyping results showed that 88% of slow, 50% of moderate, and 11% of high wilting genotypes expressed the TRlim trait at 32°C and 43, 10, and 0% at 37°C, respectively. Genetic mapping with the phenotypic data we collected revealed three QTL across two chromosomes, two associated with TRlim traits and one associated with leaf temperature. Analysis of Gene Ontologies of genes within QTL regions identified several intriguing candidate genes, including one gene that when overexpressed had previously been shown to confer enhanced tolerance to abiotic stress. Collectively these results will inform and guide ongoing efforts to understand how to deploy genetic tolerance for drought stress.

Genotype identification for a water saving trait: Exploring early stomatal closure under soil drying among mid‐South soybean

AbstractIt is necessary to understand the differences in physiological responses to water deficit stress of soybean [Glycine max (L.) Merr.] genotypes in order to breed for drought‐tolerant soybean genotypes better suited to water‐limited environments in the U.S. mid‐South region. Using controlled environment and field trials, this study identified soybean genotypes that conserve water through differences in their stomatal response under soil water deficit to determine if this trait confers a yield advantage. Research was conducted from 2017 to 2020 at the West Tennessee Research and Education Center in Jackson, TN. Seventeen mid‐South soybean genotypes (i.e., both, breeding lines and modern commercial soybean) were investigated for an early stomatal closure trait during progressive soil drying under controlled environment conditions. Under field conditions, portable rainout shelters installed when the plant canopies of most genotypes had reached at least 80% canopy closure to impose water deficit stress to nine selected genotypes for field observation of wilting score (WS) and early stomatal closure. Differences were observed among genotypes in their early stomatal closure thresholds with progressive soil drying in the controlled environment. The range in fraction of transpirable soil water (FTSW) thresholds among 17 tested genotypes was 0.33–0.76. Based on our experimental approaches in 4 yr of field studies, genotypes Ellis and USG Allen consistently expressed an early decrease in transpiration rate with progressive soil drying, delayed wilting in the field when soil water deficit developed under rainout shelters, and greater yield when grown in simulated drought conditions.

Drought resilience in CIMMYT maize lines adapted to Africa resulting from transpiration sensitivity to vapor pressure deficit and soil drying

ABSTRACT Low rainfall limits crop yield, particularly for maize (Zea mays L.) in southern Africa. Consequently, there is a need to identify genetic sources of specific drought-related traits that can contribute to soil water conservation and increased yields under water-limited conditions. In this study, maize genotypes released for production in southern Africa were tested for expression of two soil water-conservation traits: limited transpiration under elevated vapor pressure deficit (VPD) and decreased transpiration rate at high soil water contents earlier in the soil drying cycle. Two genotypes, CML 590 and CML 593, were identified and confirmed to initiate expression of limited-transpiration rate at VPD above about 1.9 kPa. In the soil-drying experiment, Umbelu 8923 and Umbelu 8930 closed their stomata earliest in the soil drying cycle as compared to other tested genotypes. These four genotypes with specific physiological traits for superior response to water deficit are genetic resources for further study to improve maize drought resilience.

Elevated CO2 Modulates Plant Hydraulic Conductance Through Regulation of PIPs Under Progressive Soil Drying in Tomato Plants.

Increasing atmospheric CO2 concentrations accompanied by abiotic stresses challenge food production worldwide. Elevated CO2 (e[CO2]) affects plant water relations via multiple mechanisms involving abscisic acid (ABA). Here, two tomato (Solanum lycopersicum) genotypes, Ailsa Craig (AC) and its ABA-deficient mutant (flacca), were used to investigate the responses of plant hydraulic conductance to e[CO2] and drought stress. Results showed that e[CO2] decreased transpiration rate (E) increased plant water use efficiency only in AC, whereas it increased daily plant water consumption and osmotic adjustment in both genotypes. Compared to growth at ambient [CO2], AC leaf and root hydraulic conductance (Kleaf and Kroot) decreased at e[CO2], which coincided with the transcriptional regulations of genes of plasma membrane intrinsic proteins (PIPs) and OPEN STOMATA 1 (OST1), and these effects were attenuated in flacca during soil drying. Severe drought stress could override the effects of e[CO2] on plant water relation characteristics. In both genotypes, drought stress resulted in decreased E, Kleaf, and Kroot accompanied by transcriptional responses of PIPs and OST1. However, under conditions combining e[CO2] and drought, some PIPs were not responsive to drought in AC, indicating that e[CO2] might disturb ABA-mediated drought responses. These results provide some new insights into mechanisms of plant hydraulic response to drought stress in a future CO2-enriched environment.

Impact of drought and temperature constraints on development and growth of faba bean (Vicia faba L.)

ABSTRACT Faba bean (Vicia faba L.) is an important traditional pulse crop in many parts of Asia and the Mediterranean region. However, water deficit and temperature, two of the key variables associated with climate variability, can have major negative influences on the development and growth of faba bean. A series of experiments were conducted to study the potential impact of temperature and water deficit on several physiological processes among faba bean genotypes. Development of node number was determined to be dependent on temperature and was found to be essentially constant among genotypes with a value of 56°C accumulated temperature required for appearance of each node. Plant leaf area, which is important in crop carbon accumulation, was estimated by developing allometric relationships between plant leaf area and number of nodes. The coefficients of these relationships varied among genotypes. Water deficit was found to be critical in impacting plant transpiration and nitrogen fixation rates. The threshold for the decrease in transpiration rate with soil drying was found to range from a fraction of transpirable soil water (FTSW) from 0.22 to 0.60 among 12 genotypes, indicating a genetic resource for improving drought resilience. Results in comparing symbiotic nitrogen fixation on drying soil among genotypes also indicated genetic variation, with one genotype (WW4403/H) being especially drought tolerant. The results of these experiments identified important genotypic differences in sensitivity of specific physiological processes to temperature and water deficit, which can be exploited to improve faba bean resilience to these environmental variables.

Silicon reduces cadmium absorption and increases root-to-shoot translocation without impacting growth in young plants of hemp (Cannabis sativa L.) on a short-term basis.

Textile hemp (Cannabis sativa L.) is a non-edible multipurpose crop suitable for fiber production and/or phytoremediation on moderately heavy metal-contaminated soils. Experiments were conducted in nutrient solution to assess the short-term impact of silicon (Si), a well-known beneficial element, on plants exposed to 20 μM cadmium (Cd) in nutrient solution. Cd decreased plant growth and affected photosynthesis through non-stomatal effects. Cd translocation factor was higher than 1, confirming the interest of hemp for phytoextraction purposes. Additional Si did not improve plant growth after 1 week of treatment but decreased Cd accumulation in all organs and improved water use efficiency through a decrease in transpiration rate. Si had only marginal impact on Cd distribution among organs. It increased glutathione and phytochelatin synthesis allowing the plants to efficiently cope with oxidative stress through the improvement of Cd sequestration on thiol groups in the roots. Si may thus have a fast impact on the plant behavior before the occurrence of plant growth stimulation.