Severe Water Deficit Conditions Research Articles

DUF4057 containing express-protein negatively regulates the drought responses in rice

The current global climatic conditions project drought as a severe form of abiotic stress that directly impacts the agricultural productivity of economically important crops. In this study, we conducted a functional characterization of a drought-responsive express-protein (OsEP) that contains the DUF-4057 superfamily domain. In silico analysis revealed differential expression of the OsEP gene in two drought-responsive rice varieties with contrasting characteristics (Heena, drought-tolerant, and Kiran, drought-sensitive). According to phylogenetic analysis, OsEP showed a high amino acid identity with the protein of Panicum hallii and Zizania palustris. Following treatment with 20% PEG, quantitative real-time PCR demonstrated an increased abundance of OsEP gene transcripts. The OsEP gene exhibited the highest expression levels in the gynoecium and roots of the rice plant. Notably, rice lines over-expressing OsEP were found to be sensitive to PEG-induced drought stress, whereas knockdown lines exhibited improved root architecture and lignification of root cells, enabling them to withstand severe water deficit conditions. Furthermore, drought stress compromised the growth parameters and grain yield of OsEP over-expressing lines compared to knock-down lines. Increased activity of antioxidant enzymes such as CAT (catalase), APX (Ascorbate peroxidase), and SOD (Superoxide Dismutase) was observed in knock-down lines compared to both over-expressing lines and wild-type plants. Additionally, knock-down lines exhibited decreased levels of membrane stability marker (MDA) and electrolyte leakage, along with elevated proline content. Important regulatory genes such as OsHsfC1b, OsbZIP81, and OsNCED, positively impacted by osmotic/drought stress, exhibit variable expression in over-expressing and knock-down lines. These findings suggest that down-regulation of the OsEP gene modulates the genomic architecture of knock-down lines, allowing them to maintain cellular homeostasis by regulating enzymatic activity. Our results indicate that the OsEP gene is a negative regulator of drought response. Moreover, GA-JA (Gibberellic Acid-Jasmonic Acid) cross-talk is involved in the down-regulation of stress-related phenomena in over-expressing lines. Overall, this study sheds light on the crucial role of the DUF4057 superfamily gene in drought response and provides insights into its potential regulatory mechanism.

Effect of Drought Stress on Growth of Soybean under Seedling Stage

The present study was conducted during September-October, 2022 at Greenhouse facility of Experimental Farm, Faculty of Agriculture Sciences, Mandsaur University, Mandsaur, Madhya Pradesh, India to identify drought tolerant genotypes. Total sixty genotypes were sown on dated 02/09/2022 by using polythene bags in completely randomized block design with four different water regimes and two replications in each set during month of September, 2022. Data were recorded for root-shoot parameters and relative leaf water content. Mean performance of root length showed that among 60 genotypes, thirty genotypes showed increased tap roots under severe water deficit conditions (0%). Under sever water stress condition (0%) highest root length was recorded of genotypes NRC138 (20.5 cm) followed by GW251 (18.15 cm) and RSC1107 (17.2 cm) respectively while lowest root length was noted in accession GW312 (3.4 cm) followed by NRC37 (5 cm) and NRC 142 (5.15 cm) respectively. Under0% water stress highest relative leaf water content was observed in genotype JS2034 (97.16%) followed by GW10 (93.47%) and GW159 (89.18%) whereas lowest was found in GW28 (20.96%) followed by GW100 (26.31%) and AGS25 (26.66%). On basis of mean data of root length, relative leaf water content, root shoot ratio by length and visual observation of plants, 11 genotypes were identified as drought tolerant and 19 genotypes were identified as medium tolerant. The identified drought tolerant genotypes may be used as water stress tolerant genotypes in future for improvement of crop in relation to drought tolerance.

Biometric and morphological adjustments of Eugenia. dysenterica DC. seedlings in response to increased soil water deficit

Water stress can affect all aspects of plant growth and development, compromising its productive potential. The cultivation of fruit species native to the Cerrado and the study of their behavior under conditions of low water availability are necessary activities, in view of their socioeconomic and environmental potential. This study was conducted to evaluate the effect of water deficit on growth and biomass production of the cagaita tree (Eugenia dysenterica DC.), a species endemic to the Cerrado (Brazilian Savannah). The experiment was performed in a greenhouse for 120 days in a randomized block design (RBD), with a double factorial arrangement (2x5), corresponding to two cagaita mother plants and five water conditions. We evaluated the growth and leaf, stem and root functional characteristics. The most severe water deficit conditions reduced shoot growth, number of leaves, production of biomass and dry matter and increased the specific and per plant mass root length of cagaita plants. Deficit extension had negative effects on its growth and development. There was a statistical difference between mother plants, with mother plant 2 being more resistant to drought. The application of a severe or longer water deficit affected shoot growth and reduced the appearance of new leaves. The stress caused by water deficiency allowed an increase in root functional characteristics, supporting the hypothesis that plants under adverse conditions focus on higher biomass production and convert a higher amount of dry matter into the roots. Leaf area did not show to be a functional characteristic, explaining the stress effects in E. dysenterica DC plants.

Plant growth promoting microorganisms (PGPM) as an eco-friendly option to mitigate water deficit in soybean (Glycine max L.): Growth, physio-biochemical properties and oil content

Drought, as an important challenge in Iran, affects all growth indicators for plants. Application of plant growth promoting microorganisms (PGPM) can reduce the detrimental effects of water deficit on plants. Two separate field experiments were conducted at the Tehran and Hashtrood sites, Iran in 2019 to study the influences of Azotobacter chroococcum (Az) and Piriformospora indica (Pi) or Az + Pi on growth, physio-biochemical properties and oil content of soybean (Glycine max L.) under water deficit conditions. Although water deficit dramatically reduced the plant height, percent vegetation cover and relative water content (RWC), plots treated with Az and Pi exhibited higher performance mentioned traits at both sites. Besides, co-inoculation of Az and Pi increased proline in Tehran (48.85 and 29.24% in leaf and root, respectively) and Hashtrood (46.91 and 48.91% in leaf and root, respectively) under severe water deficit. Accumulation of glycine betaine, soluble sugars and proteins increased for plots which received Az and Pi. Under severe water deficit conditions, the co-inoculation with Az and Pi enhanced the oil content of soybean by 12.87 and 9.37% at Tehran and Hashtrood sites respectively. Application of Az and Pi resulted in reducing the adverse effects of water deficit on oil quality of soybean by increasing the linoleic and linolenic acid in oil. Moreover, inoculation of soybean with Az and Pi can provide drought tolerance by improving ascorbate peroxidase (APX), catalase (CAT), superoxide dismutase (SOD) and peroxidase (POX) activity. However, co-inoculation with Az and Pi was generally more effective in the alleviation of water deficit detrimental effects than sole inoculation with Az and Pi. Consequently, it can be a good approach for improving tolerance, growth and oil production of soybean under water deficit conditions.

Response of dew and hydraulic redistribution to soil water in a rainfed dryland jujube plantation in China’s Hilly Loess Region

Soil desiccation occurs widely across China’s Loess Plateau due to long-term water demand in excess of water supply. Hydraulic redistribution (HR) - the movement of water from wet to dry soil via roots - and canopy dew (CD) are crucial to water replenishment in dryland ecosystems. However, much is still not known about the response of CD and HR to soil water deficits (including no deficit, slight deficit, moderate deficit, and severe deficit water conditions) in dryland jujube (Ziziphus jujuba Mill.) plantations in China’s Hilly Loess Region. To this end, the duration and intensity of dew were monitored using dielectric leaf wetness sensors to better understand the effects of soil water status on dew. Also, soil water content, sap flow, and meteorological variables were measured during the jujube growing seasons in 2017–2019. The results showed that the time of occurrence of CD under the no deficit condition came earlier than the time of occurrence of CD under slight, moderate, and severe soil water deficit conditions. Peak CD appeared at 5:00–6:30 am and ended at 6:30–9:00 am local time under the four soil water conditions. The amount, duration, and frequency of CD decreased with increasing soil water deficit. The amount and duration of CD under the no deficit condition were significantly higher than under the slight, moderate, and severe soil water deficit conditions (p < 0.05). The amount and frequency of HR (in the 20–60 cm soil layer) increased with increasing soil water deficit. Under the no deficit condition, HR was significantly lower than under the slight, moderate, and severe soil water deficit conditions (p < 0.05). While HR was influenced by CD, CD enhanced HR under the no deficit condition, but inhibited HR under slight, moderate, and severe soil water deficit conditions. For the growing season, the contribution of CD to total actual evapotranspiration (ETc act, CD/ ETc act ratio) was highest under the no deficit condition (maximum CD/ ETc act ratio of 0.21). The contribution of HR to ETc act (HR/ ETc act ratio) was higher under slight, moderate, and severe soil water deficit conditions (maximum of 0.11). The mutual effects of CD and HR lessened soil water deficit, making them important ecohydrological processes affecting the response of dryland jujube plantations to soil desiccation.

Impact of Deficit Irrigation on Grapevine cv. 'Touriga Nacional' during Three Seasons in Douro Region: An Agronomical and Metabolomics Approach.

The introduction of irrigation in vineyards of the Mediterranean basin is a matter of debate, in particular in those of the Douro Demarcated Region (DDR), due to the limited number of available studies. Here, we aimed to perform a robust analysis in three consecutive vintages (2018, 2019, and 2020) on the impact of deficit irrigation on the yield, berry quality traits, and metabolome of cv. ‘Touriga Nacional’. Results showed that in the peaks of extreme drought, irrigation at 30% crop evapotranspiration (ETc) (R30) was able to prevent a decay of up to 0.4 MPa of leaf predawn water potential (ΨPd), but irrigation at 70% ETc (R70) did not translate into additional protection against drought stress. Following three seasons of irrigation, the yield was significantly improved in vines irrigated at R30, whereas irrigation at R70 positively affected the yield only in the 2020 season. Berry quality traits at harvest were not significantly changed by irrigation, except for Total Soluble Solids (TSS) in 2018. A UPLC–MS-based targeted metabolomic analysis identified eight classes of compounds, amino acids, phenolic acids, stilbenoid DP1, stilbenoid DP2, flavonols, flavan-3-ols, di-OH- and tri-OH anthocyanins, and showed that anthocyanins and phenolic acids did not change significantly with irrigation. The present study showed that deficit irrigation partially mitigated the severe summer water deficit conditions in the DDR but did not significantly change key metabolites.

Control of Substrate Water Availability Using Soil Sensors and Effects of Water Deficit on the Morphology and Physiology of Potted Hebe andersonii

Many plant producers tend to overwater crops to prevent water stress and salt-induced damage. These practices waste irrigation water and cause leaching that harms the environment and increases production costs. In order to optimize water consumption and minimize the environmental impact of plant production, this study aimed to determine the physiological and morphological responses of Hebe andersonii to three substrate volumetric water contents (49%, 39%, and 32%). The experiment was conducted in a greenhouse with an irrigation protocol that consisted of adding small volumes of water to avoid leaching while monitoring substrate moisture with dielectric soil sensors. The results showed that moderately low substrate moisture improved the water-use efficiency, while growth was significantly reduced under more severe water deficit conditions (but without leaf chlorosis or abscission). The photosynthetic activity of Hebe was primarily controlled by the stomatal aperture, which was co-determined by the substrate moisture and seasonal temperature. Hebe leaves promoted non-photochemical quenching when carbon assimilation was limited by a water deficit, and accumulated solutes through an osmotic adjustment process (especially Cl−, Na+, and K+) to maintain their water status. Overall, Hebe andersoni cv. Variegata could successfully grow and improve its water-use efficiency in low substrate moisture and under a non-draining irrigation regime.

Transcriptomic and Biochemical Analysis Reveal Integrative Pathways Between Carbon and Nitrogen Metabolism in Guzmania monostachia (Bromeliaceae) Under Drought.

Most epiphytes are found in low-nutrient environments with an intermittent water supply. To deal with water limitation, many bromeliads perform crassulacean acid metabolism (CAM), such as Guzmania monostachia, which shifts from C3 to CAM and can recycle CO2 from the respiration while stomata remain closed during daytime and nighttime (CAM-idling mode). Since the absorbing leaf trichomes can be in contact with organic (urea) and inorganic nutrients (NO3−, NH4+) and the urea hydrolysis releases NH4+ and CO2, we hypothesized that urea can integrate the N and C metabolism during periods of severe drought. Under this condition, NH4+ can be assimilated into amino acids through glutamine synthetase (GS), while the CO2 can be pre-fixated by phosphoenolpyruvate carboxylase (PEPC). In this context, we evaluated the foliar transcriptome of G. monostachia to compare the relative gene expression of some genes involved with CAM and the N metabolism when bromeliads were submitted to 7days of drought. We also conducted a controlled experiment with an extended water deficit period (21days) in which bromeliads were cultivated in different N sources (urea, NH4+, and NO3−). Our transcriptome results demonstrated an increment in the expression of genes related to CAM, particularly those involved in the carboxylation metabolism (PEPC1, PPCK, and NAD-MDH), the movement of malate through vacuolar membrane (ALMT9), and the decarboxylation process (PEPCK). Urea stimulated the expression of PEPC1 and ALMT9, while Urease transcripts increased under water deficit. Under this same condition, GS1 gene expression increased, indicating that the NH4+ from urea hydrolysis can be assimilated in the cytosol. We suggest that the link between C and N metabolism occurred through the supply of carbon skeleton (2-oxoglutarate, 2-OG) by the cytosolic isocitrate dehydrogenase since the number of NADP-ICDH transcripts was also higher under drought conditions. These findings indicate that while urea hydrolysis provides NH4+ that can be consumed by glutamine synthetase-cytosolic/glutamate synthase (GS1/GOGAT) cycle, the CO2 can be used by CAM, maintaining photosynthetic efficiency even when most stomata remain closed 24h (CAM-idling) as in the case of a severe water deficit condition. Thus, we suggest that urea could be used by G. monostachia as a strategy to increase its survival under drought, integrating N and C metabolism.

Detection of Epistasis for Seed and Some Phytochemical Traits in Coriander under Different Irrigation Regimes

Coriander (Coriander sativum L.) is an annual herb mainly cultivated for its seed characteristics. Drought stress is a major problem which affects coriander behaviour through biochemical responses. This study aimed to determine the nature and magnitude of epistasis in inheritance of seed yield (SY), percent of dehulled seed (PODS), percent of seed hulls (POSH), essential oil content (EOC), essential oil yield (EOY), dehulled seed fatty acid content (DSFAC), hull fatty acid content (HFAC), fatty acid content (FAC), and fatty acid yield (FAY), and to estimate additive and dominance variance for the traits not influenced by epistasic effects. Three testers, TN-59-158 (highly drought-susceptible), TN-58-230 (highly drought-tolerant, but low-yielding), and their F1 hybrid were each crossed for six genotypes. The experiment was performed under different levels of water deficit: control (C), moderate water deficit (MWD), and severe water deficit (SWD) conditions. Epistasis affected the expression of SY, EOC, EOY, FAC, and FAY in all water conditions, PODS in C, POSH in SWD, HFAC in MWD, and DSFAC in both C and MWD conditions. Total epistasic effects were partitioned, showing that both [i] and [j + l] type interactions were significant, with a prevalent influence of [i] type interactions on these traits except for POSH and FAC in the SWD condition, which exhibited a higher value of the [j + l] type. Both additive and non-additive gene actions were significant for those traits not significantly affected by epistasis in C, MWD, or SWD conditions. An additive type of gene action was preponderant for PODS in MWD and SWD, POSH in MWD, DSFAC in SWD, and HFAC in C and SWD conditions.

Transcriptomic analyses provide new insights into jujube fruit quality affected by water deficit stress

Water availability is a crucial factor affecting fruit quality and productivity. A period of mild drought stress can increase fruit sweetness and improve fruit quality. However, the mechanism underlying the transcriptional regulation in Chinese jujube under water deficit conditions remains relatively uncharacterized. In this study, we analyzed the protein and sugar contents, the average weight, and transcript expression (RNA sequencing) of jujube fruit at different ripening stages (i.e., white mature and half-red fruit) under mild and severe water deficit conditions. The sucrose and protein contents increased significantly under water deficit conditions. The increase in water deficit stress from mild to severe did not significantly alter the sugar accumulation, but it decreased the average fruit weight. The sugar- and amino acid-related pathways, flavonoid biosynthesis, xyloglucan metabolism, and phenylpropanoid biosynthesis were affected by water deficit stress. Gene co-expression analyses identified many ABA- and ethylene-related genes with expression levels modulated by water deficit conditions, especially in the half-red stage. Additionally, we identified the key genes affecting fruit sugars, pigments, cell wall polysaccharides, and phenylpropanoids, which influence fruit quality. Notably, genes related to sugar transporters rather than sugar metabolism contributed to the sucrose accumulation. Flavonoid synthesis-related gene expression contributed to the earlier coloration of the stressed fruit than of the control fruit. Severe water deficit stress up-regulated the expression of pectinesterase and endotransglucosylase/hydrolase genes, which accelerated fruit ripening and softening. Regarding the phenylpropanoid biosynthesis pathway, the exposure to mild water deficit stress promoted the synthesis of secondary metabolites useful to humans (e.g., coniferin and syringin), whereas the severe water deficit treatment increased lignin accumulation. Considered together, these findings revealed the transcriptional regulatory mechanism that improved jujube fruit quality under mild drought conditions. Furthermore, the results of this study may be useful for optimizing the irrigation during jujube cultivation.

Primary Metabolite Profile Changes in Coffea spp. Promoted by Single and Combined Exposure to Drought and Elevated CO2 Concentration.

Climate change scenarios pose major threats to many crops worldwide, including coffee. We explored the primary metabolite responses in two Coffea genotypes, C. canephora cv. Conilon Clone 153 and C. arabica cv. Icatu, grown at normal (aCO2) or elevated (eCO2) CO2 concentrations of 380 or 700 ppm, respectively, under well-watered (WW), moderate (MWD), or severe (SWD) water deficit conditions, in order to assess coffee responses to drought and how eCO2 can influence such responses. Primary metabolites were analyzed with a gas chromatography time-of-flight mass spectrometry metabolomics platform (GC-TOF-MS). A total of 48 primary metabolites were identified in both genotypes (23 amino acids and derivatives, 10 organic acids, 11 sugars, and 4 other metabolites), with differences recorded in both genotypes. Increased metabolite levels were observed in CL153 plants under single and combined conditions of aCO2 and drought (MWD and SWD), as opposed to the observed decreased levels under eCO2 in both drought conditions. In contrast, Icatu showed minor differences under MWD, and increased levels (especially amino acids) only under SWD at both CO2 concentration conditions, although with a tendency towards greater increases under eCO2. Altogether, CL153 demonstrated large impact under MWD, and seemed not to benefit from eCO2 in either MWD and SWD, in contrast with Icatu.

Assessment of morpho-physiological and quantitative and qualitative yield of Peppermint (Mentha piperita L.) under different irrigation regimes and application of different nitrogen fertilizer

Introduction Water and nitrogen fertilizer are major determinants of the level of agricultural production in the world, in addition to the quantity and quality of Medicinal plants are also effective. Iran's climate is mainly dry and semi-arid, in such a situation, where abnormal environmental stresses occur for plants. Improving crop yields in these stress conditions require good management of inputs (such as water and nutrients), their amount and type, and knowledge of physiological processes and plant defense mechanisms is essential. Water stress can significantly alter the metabolism of plants and reduce growth and photosynthesis and ultimately yield of plants. In this situation, effective management of water consumption in agriculture is an urgent necessity. In this regard, the use of agronomic techniques such as application of organic fertilizers or enhancement of soil biological conditions may be effective in reducing the effects of water stress and less use of chemical fertilizers for sustainable agriculture and human nutritional health. Also, intensive agriculture with the widespread use of chemical fertilizers, especially nitrogen can cause an increase in costs and environmental pollution. A key component of sustainable agriculture is use of organic fertilizers such as vermicompost and azocompost. Materials and methods In order to investigate the effects of water deficit stress and different nitrogen fertilizers on morphological, physiological traits, biological yield and essential oil percentage of peppermint, a experiment was conducted in a factorial arrangement in a randomized complete block de sign with three replications were carried out in 2018 at the field research station of the Agricultural Research Center of Tarbiat Modares University in Karaj (51 10’E, 33 44’ N, 1305.2 m above sea level). Experimental treatments consisted of three irrigation regimes (irrigation up to field capacity and after unloading 25, 40 and 55% water use in root zone, respectively) as the major factor and six fertilizer treatments based on nitrogen requirement respectively (100% chemical fertilizer, no fertilizer, 50% chemical + 50% azocompost, 100% vermicompost, 100% azocompost and 50% chemical fertilizer + 50% vermicompost) were as sub-factors. After field preparations, this area was divided into 54 experimental plots each of which were 2 m long with six rows, 0.2 m apart. Between all the main plots, a 3 m alley was kept to eliminate the influence of lateral water movement. Plant to plant distance in each row was 0.2 cm. Results Analysis of variance showed that the effect of all the experimental treatments and their interaction on all measured traits was significant. The results showed that mild and severe drought stress decreased plant height (18.2 and 42.92%) and biological yield (15.11 and 51.98%, respectively), while pigment, carotenoid, anthocyanin, proline and essential oil percentage increased. Nitrogen fertilizer application increased all measured traits. In most of the traits measured in this experiment, 50% chemical fertilizer and 50% vermicompost fertilizer were evaluated even better under severe water deficit conditions than other treatments. Conclusion: The results also showed that if the aim of planting peppermint is to improve the quality (essential oil percentage) of the plant by applying high water deficit stress, it can save more than 50% water consumption by producing the highest essential oil percentage. And vermicompost fertilizer can also be substituted for nitrogen chemical fertilizer to promote safe and sustainable

Bacterial Inoculants Mitigating Water Scarcity in Tomato: The Importance of Long-Term in vivo Experiments.

Global population growth and climate change raise a challenge to agriculture, which, combined with the issues concerning the use of chemical fertilizers, have generated increasing attention in the use of plant-associated bacteria as a sustainable strategy in agri-food systems. The objective of this study is to evaluate the ability of five bacterial strains, previously isolated from the rhizosphere or endosphere of plants adapted to harsh environmental conditions, to act as potential plant biofertilizers in different conditions of water availability. The strain biosafety for a deliberate environmental release was investigated through a literature survey and antibiotic resistance testing. The selected strains were first characterized for their plant growth–promoting (PGP) and rhizocompetence-related traits through in vitro assays and then on short-term in vivo experiments on tomato plants. A long-term greenhouse experiment was further conducted to monitor the PGP effect of the bacteria during the entire life cycle of tomato plants subjected to full irrigation or to severe water deficit conditions, aiming to assess their actual effect on plant productivity, which is the ultimate target of the agricultural sector. Some of the strains showed a potential in improving water use efficiency and mitigating plant water stress. Under severe irrigation deficit, four of the tested strains, Micrococcus yunnanensis M1, Bacillus simplex RP-26, Pseudomonas stutzeri SR7-77, and Paenarthrobacter nitroguajacolicus 2–50, significantly increased the number of productive plants in comparison to non-bacterized control ones. Two of them, Bacillus simplex RP-26 and Paenarthrobacter nitroguajacolicus 2–50, demonstrated also, under full irrigation, to significantly improve the water productivity in comparison with non-bacterized plants. Despite all the strains showed promising PGP potential in short-term assays, the positive effect of the bacterial inoculants on plant physiology and fruit yield was observed in some cases but never corroborated by statistical significance. These results highlight the importance of performing long-term in vivo experiments to define the real PGP ability of a bacterial inoculant to positively impact plant production.

Responses of Amygdalus pedunculata Pall. in the sandy and loamy soils to water stress

Amygdalus pedunculata Pall. is a major species that is widely planted in afforested soils with different textures in the transitional zone between Mu Us Desert and Loess Plateau, China. However, the responses of A. pedunculata to increasing intensity of water stress in different textural soils are not clear. Here, we conducted a soil column experiment to evaluate the effects of different textures (sandy and loamy) on water consumption, water use efficiency (WUE), biomass accumulation and ecological adaptability of A. pedunculata under increasing water stress, i.e., 90% (±5%) FC (field capacity), 75% (±5%) FC, 60% (±5%) FC, 45% (±5%) FC and 30% (±5%) FC in 2018. A. pedunculata grown in the sandy soil with the lowest (30% FC) and highest (90% FC) water contents had respectively 21.3%–37.0% and 4.4%–20.4% less transpiration than those with other water treatments (45%–75% FC). In contrast, A. pedunculata transpiration in the loamy soil decreased with decreasing water content. The magnitude of decrease in transpiration increased with increasing level of water deficit (45% and 30% FC). Mean daily and cumulative transpirations of the plant were significantly lower in the sandy soil than in the loamy soil under good water condition (90% FC), but the reverse was noted under water deficit treatments (45% and 30% FC). Plant height, stem diameter and total biomass initially increased with decreasing water content from 90% to 75% FC and then declined under severe water deficit conditions (45% and 30% FC) in the sandy soil. However, these plant parameters decreased with decreasing water content in the loamy soil. WUE in the sandy soil was 7.8%–12.3% higher than that in the loamy soil, which initially increased with decreasing water content from 90% to 75% FC and then declined under water deficit conditions (45% and 30% FC). The study showed that plant transpiration, biomass production and WUE responded differentially to increasing intensity of water stress in the sandy and loamy soils. The contrasting responses of A. pedunculata to water stress in different textural soils can guide future revegetation programs in the northern region of Chinese Loess Plateau by considering plant adaptability to varying soil and water conditions.

Integrated application of biochar and bio-fertilizer improves yield and yield components of Cowpea under water-deficient stress

A low amount of organic matter and insufficient irrigation are two main challenges facing successful crop production in arid and semiarid regions. Application of biochar as an organic amendment to soil not only can help increase organic matter in soil, but also may alleviate adverse effects of water deficit on plant growth and yield production. To test this hypothesis, a two-year field experiment was conducted to assess the effect of sugarcane biochar on yield and yield components of cowpea in water-deficient soil. Treatments consisted of two levels of seed treatment with nitroxin, three levels of biochar application (0, 4, and 8 ton/ha), and a threelevel irrigation regime (60, 90, and 120 mm from evaporation pan class A), laid out in a split-factorial design. Results showed that the seed number per plant was significantly higher in cowpea when grown with biochar, possibly due to the relief of water-deficient stress and higher phosphorus and potassium content. Biomass production of cowpea declined under a severe waterdeficit condition (ir3) compared to normal irrigation (ir1) in 2018 and 2019, decreasing by 39% and 42%, respectively. The maximum biomass obtained from application of 8 ton/ha biochar reached 617.43 and 664.92 g/m2 in 2018 and 2019, respectively. Seeds treated with nitroxin exhibited 10% and 8% greater biomass production in 2018 and 2019 as compared with control treatments. Seed yield increased with the addition of biochar to soil under all irrigation regimes; however, the maximum seed yield of 266.46 and 275.36 g/m2 was observed when there was no water-deficient stress condition and application of 8 ton/ha biochar in 2018 and 2019, respectively.

Spectral behavior of Persian oak under compound stress of water deficit and dust storm

Persian oak (Quercus Brantii Lindl.) which is the most widely distributed tree in the Zagros Mountain forests is affected by western dust storms, mostly originating in Iraq, and harsh water stress as well. The objective of this research is to analyze the spectral behavior of Persian oak under water and dust stress scenarios, aiming to pave the way for modeling the stresses of drought and dust storms on oak trees using remote sensing images. Experiments were carried out on 54 two-year old oak tree seedlings, using a portable wind tunnel in greenhouse conditions. Water stress was induced on seedlings by means of changes in irrigation practices, i.e. well-watered (100 % field capacity), medium water deficit condition (40 % field capacity), and severe water deficit condition (20 % field capacity) treatments. Dust stress is also investigated by using three different dust particle concentrations, i.e. 350, 750 and 1500 (μg/m³). The spectrometry experiments were carried out at leaf and canopy levels in dark room by Fieldspec-3-ASD spectrometer. Spectral analysis was conducted using four procedures: (i) narrow-band spectral indices analysis, (ii) geometric indicators extraction from absorption features, (iii) Partial Least Squares Regression (PLSR), and SVM classifier. Results show that water stress could be modeled much better using PLSR statistic (R2 = 0.87, RMSE = 0.12), narrow-band indices analysis (R2cv = 0.75, RMSEcv = 0.17), and continuum removal (R2 = 0.71, RMSE = 0.20), respectively. For dust stress, PLSR (R2 = 0.83, RMSE = 0.14) and narrow-band indices (R2cv = 0.7, RMSE cv = 0.30) showed the best results, respectively. SVM could successfully separate stressed and not-stressed samples and also the stress types at both leaf and canopy levels, but it could not distinguish the different levels of stresses.

Soil fertility and fine root distribution after gypsum application in Eucalyptus plantations with different tolerance to water deficit

Most Eucalyptus plantations in Brazil are located in regions with low fertility soils and seasonal droughts. The main objectives of the present study were to evaluate the fine root distribution of Eucalyptus along the soil profile and the vertical distribution of Ca, Mg, S, and K in the soil in response to dolomitic limestone and gypsum application under severe water deficit conditions. The experiment was designed in randomized blocks. Two clones of the hybrid Eucalyptus urograndis (one clone was tolerant to water deficit and one clone was susceptible to water deficit) were used under two crop conditions (with and without gypsum application). Fine root density (FRD) and root length density (RLD) decreased gradually along the soil profile. Gypsum application increased RLD in some soil layers in the tolerant clone. The Ca, Mg, and S-SO42− content of the soil increased in both clones. Both clones showed an increase in wood volume in response to gypsum application. The Ca, Mg, and S-SO42− content of the soil increased in both clones. Both clones showed an increase in wood volume in response to gypsum application. At 46 months after planting, the wood volume increased by 17% in the susceptible clone and by 24% in the tolerant clone. The use of soil conditioners, such as gypsum and limestone, is important to improve soil fertility and root distribution for both clones, especially in a prolonged drought season.

Effect of nylon mulch and some plant growth regulators on water use efficiency and some quantitative traits in onion (Allium cepacv.) under water deficit stress

In order to investigate the effects of plant growth regulators (PGRs) and mulch on some traits of onion under water deficit stress, a split-factorial experiment based on Randomized Complete Block Design with three replications was conducted in Iran in 2016 and 2017. The main plot consisted of water deficit stress treatment at three levels (100%, 80% and 60% of water requirement), and sub-plots consisted of a dark nylon mulch application and an unmulched control, and PGRs six levels (zero, salicylic acid 0.5 mM, methyl jasmonate 5 and 7.5 mM, and 24-epibrasinolide 0.5 and 1 mM, respectively). Final yield under water deficit stress (60% water requirement) decreased by 30% compared to control (100% water requirement). On the other hand, the use of plastic mulch increased the yield by 29%. Interaction of water deficit stress and PGRs on leaf number, fresh and dry weight of plant, plant height, bulb length and diameter, early yield and final bulb yield were significant and the effect of regulators was mainly effective in severe water deficit conditions. The highest crop yield of 52.55 ton per hectare was obtained from 1 micromolar brassinolide treatment under non-stress conditions which had a 9% increase compared to control under non-stress conditions and 28% increase compared to control under severe water deficit stress.

Photosynthesis response to severe water deficit in terminal stems of Myriolimon ferulaceum

Myriolimon ferulaceum is a leafless species and close relative to Limonium inhabiting the same harsh environments in the rocky coast and salt marshes, with discontinuous distribution in western and central coast of the Mediterranean Basin and southern Iberian Peninsula. In order to test for the drought adaptive importance of photosynthesis in stems, and to decipher advantages and drawbacks of stem vs. leaf photosynthesis under drought conditions, M. ferulaceum was grown under the well-watered and severe water deficit conditions used in previous experiments with Limonium. Growth, stem anatomy, photosynthesis and gas exchange, and Rubisco-related traits were measured. Growth capacity in M. ferulaceum was higher than that of many Limonium under well-watered conditions, where limitations to photosynthesis were mostly biochemical. However, severe water deficit conditions had a higher impact in the leafless species, where the main photosynthesis limitation was stomatal conductance. High intrinsic water-use efficiency under well-watered conditions and high mesophyll conductance to stomatal conductance ratio under severe water deficit conditions were the main drivers of growth capacity in M. ferulaceum.

Effect of Water Stress during Grain Filling on Yield, Quality and Physiological Traits of Illpa and Rainbow Quinoa (Chenopodium quinoa Willd.) Cultivars.

The total area under quinoa (Chenopodium quinoa Willd.) cultivation and the consumption of its grain have increased in recent years because of its nutritional properties and ability to grow under adverse conditions, such as drought. Climate change scenarios predict extended periods of drought and this has emphasized the need for new crops that are tolerant to these conditions. The main goal of this work was to evaluate crop yield and quality parameters and to characterize the physiology of two varieties of quinoa grown under water deficit in greenhouse conditions. Two varieties of quinoa from the Chilean coast (Rainbow) and altiplano (Illpa) were used, grown under full irrigation or two different levels of water deficit applied during the grain filling period. There were no marked differences in yield and quality parameters between treatments, but the root biomass was higher in plants grown under severe water deficit conditions compared to control. Photosynthesis, transpiration and stomatal conductance decreased with increased water stress in both cultivars, but the coastal variety showed higher water use efficiency and less discrimination of 13C under water deficit. This response was associated with greater root development and a better stomatal opening adjustment, especially in the case of Rainbow. The capacity of Rainbow to increase its osmoregulant content (compounds such as proline, glutamine, glutamate, K and Na) could enable a potential osmotic adjustment in this variety. Moreover, the lower stomatal opening and transpiration rates were also associated with higher leaf ABA concentration values detected in Rainbow. We found negative logarithmic relationships between stomatal conductance and leaf ABA concentration in both varieties, with significant R2 values of 0.50 and 0.22 in Rainbow and Illpa, respectively. These moderate-to-medium values suggest that, in addition to ABA signaling, other causes for stomatal closure in quinoa under drought such as hydraulic regulation may play a role. In conclusion, this work showed that two quinoa cultivars use different strategies in the face of water deficit stress, and these prevent decreases in grain yield and quality under drought conditions.