Levels Of Water Deficit Research Articles

Deficit irrigation decision-making of indigowoad root based on a model coupling fuzzy theory and grey relational analysis

Water scarcity is a critical constraint to the cultivation of medicinal crops. Establishing irrigation requirements for medicinal plants is crucial for the large-scale production of crude drugs in China. To evaluate the response of indigowoad root growth to water deficit (WD) under-mulched drip irrigation, and determine the optimal deficit irrigation mode for this medicinal crop in Hexi Corridor’s desert oasis, two WD levels were applied: mild (65–75% FC [field capacity]) and moderate (55–65% FC). These treatments were implemented during the vegetative growth (VG) and fleshy-root growth (RG) stages, and sufficient water supply maintained during the other plant stages. A total of seven combined treatments were imposed, with sufficient water supply (85–75% FC) as the control treatment. From the 2-year-long (2017, 2018) field experiment’s results, 12 indicators of indigowoad root growth, yield, water consumption and quality attributes were evaluated via weighted fuzzy evaluation and a grey relation-coupling model. Results indicated that, with greater irrigation amounts throughout the plant growth period, the fuzzy evaluation value of growth, yield and water consumption indicators increased whereas their quality indicators decreased. The fuzzy evaluation value of yield indicators of V1G0 (mild WD treatment during VG) was the highest (0.1582, 0.1581), while that of growth indicators was also relatively high (0.1524, 0.1532). Fuzzy evaluation values of growth and yield indicators of V1G1 (mild WD during VG and RG) exceeded those of V1G2 (mild WD during VG and moderate WD during RG), but evaluation value of quality indicators was lower for V1G1 (0.1457, 0.1457) than V1G2 (0.1494, 15155). Based on the weighted grey relation model, the comprehensive score of V1G0 was deemed best. Therefore, to ensure both yield and quality, the V1G1 is recommended. Our results can provide a scientific basis for efficient water-saving cultivation of indigowoad root in Hexi oasis regions.

Dual effect of the presence of fruits on leaf gas exchange and water relations of olive trees.

The presence of fruits provokes significant modifications in plant water relations and leaf gas exchange. The underlying processes driving these modifications are still uncertain and likely depend on the water deficit level. Our objective was to explain and track the modification of leaf-water relations by the presence of fruits and water deficit. With this aim, net photosynthesis rate (AN), stomatal conductance (gs), leaf osmotic potential (Ψπ), leaf soluble sugars and daily changes in a variable related to leaf turgor (leaf patch pressure) were measured in olive trees with and without fruits at the same time, under well-watered (WW) and water stress (WS) conditions. Leaf gas exchange was increased by the presence of fruits, this effect being observed mainly in WW trees, likely because under severe water stress, the dominant process is the response of the plant to the water stress and the presence of fruits has less impact on the leaf gas exchange. Ψπ was also higher for WW trees with fruits than for WW trees without fruits. Moreover, leaves from trees without fruits presented higher concentrations of soluble sugars and starch than leaves from trees with fruits for both WW and WS, these differences matching those found in Ψπ. Thus, the sugar accumulation would have had a dual effect because on one hand, it decreased Ψπ, and on the other hand, it would have downregulated AN, and finally gs in WW trees. Interestingly, the modification of Ψπ by the presence of fruits affected turgor in WW trees, the change in which can be identified with leaf turgor sensors. We conclude that plant water relationships and leaf gas exchange are modified by the presence of fruits through their effect on the export of sugars from leaves to fruits. The possibility of automatically identifying the onset of sugar demand by the fruit through the use of sensors, in addition to the water stress produced by soil water deficit and atmosphere drought, could be of great help for fruit orchard management in the future.

Improved feed forward with bald eagle search for conjunctive water management in deficit region

Due to increasing requirements on water resources and a lower recharge rate, the farming seasons are a vital season for the management of groundwater and surface water resource management. This condition necessitates the use of combined water distribution to meet the full water requirements. Analysis of existing surface water resources and related restrictions, this research suggested an algorithm for aquifer stabilization and fulfilling optimum water requirements. To manage the optimum withdrawals and the subsequent drop, this technique first employed the MODFLOW model for simulating the water levels. Next, an improved feed-forward neural network (IFFNN) was combined with an optimization method to create a machine learning (ML) framework. During the last phase, the findings of the optimized connectives approach as well as the relevant fields technologies to determine using improved bald eagle search with least square SVM(IBES-LSSVM) method that predicted the level of water deficit for every period, especially during farming seasons. This approach is based on an improved bald eagle search (IBES) optimization technique for finding the best settings for a least-squares support vector machine (LSSVM). The findings revealed that between 2005 and 2020, the year with the biggest water deficit was 2018 when only roughly 64 percent of water need was satisfied by groundwater (69 percent) and surface water (64 percent) (33 percent). The water depth may have risen by around 0.7 m during the study period if the optimum model had been used. The outcome of this research will help the management forecast future water shortages and make smarter water strategic choices.

Riego deficitario en maíz y soja

In regions with temperate and humid climate such as Uruguay, supplementary irrigation stabilizes and increases crop yields. Irrigation on demand generates higher water consumption, which affects production system sustainability due to inefficient use of resources. In order to determine environmentally and economically more sustainable irrigation strategies, three maximum irrigation depths were evaluated in field experiment, (T2) 3 mm d-1, (T3) 6 mm d-1, (T4) 9 mm d-1 and (T1) control without irrigation, on corn and soybean production. Performance differences were observed in both crops at different water deficit levels. When precipitation (PP) was higher than average, its poor temporary distribution generated water deficit at specific times, affecting yield. T1 and T2 did not cover the crop evapotranspiration (ETc) during the critical period and grain filling, which lowered yields. T3 and T4 gave higher yields and in the three years average they were significantly different. T3 did not always cover the ETc, but the soil reserve and PP contributed to cover it, saving irrigation water. The AquaCrop model was calibrated for maize and different irrigation strategies were evaluated. The calibrated model simulated well yield, biomass and soil moisture in the irrigated treatments. In T1, the model underestimated the yield. The soil allowed for further root exploration. At 0.90 m depth, the model simulated well the yield in T1, mainly in the dry year. The model predicts the yield with a good adjustment at different irrigation and PP situations if the stress coefficients are adjusted and the crop is properly parameterized. Finally, T1, three maximum irrigation depths (3, 6 and 8 mm net) and three irrigation management (depleting 10 mm, depleting 50 % of readily available water (RAW) and depleting 100 % of RAW) were evaluated in maize with AquaCrop. The productive variables, irrigation requirement, energy demand and partial income analysis were analyzed, considering a maize crop irrigated by central pivot. It is concluded that 5 mm net gives returns and income similar to 8 mm net, without considering investment costs. Regarding management, depleting 100 % of the RAW has higher water productivity, but it is risky in dry years; however, it is feasible to vary the strategy depending on the climatic perspectives of each year.

Enhancing drought stress tolerance in Camelina (Camelina sativa L.) through exogenous application of potassium.

The current study was performed under controlled conditions to study the effects of exogenous potassium application on carotenoid contents and drought tolerance in Camelina. Water deficit levels such as 100% FC (control) and 40% FC (drought stress) were imposed after germination of Camelina plants grown to maturity, and different treatments of exogenous K+ were applied at the vegetative stage. We have reported 17 traits of plant growth, physiology, antioxidant enzyme activity, focusing on carotenoids in Camelina to explore their potential yield and yield components. For this purpose, we used multivariate analysis techniques (descriptive statistics, correlation matrix, analysis of variance [ANOVA] and principal components analysis [PCA] to determine the best relation between potassium and studied traits). The results showed a large number of variations in the studied trait under control and water deficit condition. Plant fresh weight (g) was negatively correlated with shoot length and SOD insignificantly correlated with plant fresh weight (g) under water deficit conditions. Potassium loading predicted that foliar application (3 mM K2 SO4 ), foliar application (6 mM KNO3 ), foliar application (12 mM KNO3 ) and foliar application (12 mM K2 SO4 ) are the important doses that contribute the most to enhance the growth, physiological and biochemical activities and carotenoids to improve the Camelina yield under water deficit condition. These doses should be considered in the future to improve the Camelina yield under semi-arid conditions with increased genetic diversity (varietal selection).

MicroRNAs expression profiles in early responses to different levels of water deficit in Setaria viridis.

The online version contains supplementary material available at 10.1007/s12298-022-01226-z.

Metabolomics analysis of milk thistle lipids to identify drought-tolerant genes

Milk thistle is an oil and medicinal crop known as an alternative oil crop with a high level of unsaturated fatty acids, which makes it a favorable edible oil for use in food production. To evaluate the importance of Milk thistle lipids in drought tolerance, an experiment was performed in field conditions under three different water deficit levels (Field capacity (FC), 70% FC and 40% FC). After harvesting seeds of the plant, their oily and methanolic extracts were isolated, and subsequently, types and amounts of lipids were measured using GC–MS. Genes and enzymes engaged in biosynthesizing of these lipids were identified and their expression in Arabidopsis was investigated under similar conditions. The results showed that content of almost all measured lipids of milk thistle decreased under severe drought stress, but genes (belonged to Arabidopsis), which were involved in their biosynthetic pathway showed different expression patterns. Genes biosynthesizing lipids, which had significant amounts were selected and their gene and metabolic network were established. Two networks were correlated, and for each pathway, their lipids and respective biosynthesizing genes were grouped together. Four up-regulated genes including PXG3, LOX2, CYP710A1, PAL and 4 down-regulated genes including FATA2, CYP86A1, LACS3, PLA2-ALPHA were selected. The expression of these eight genes in milk thistle was similar to Arabidopsis under drought stress. Thus, PXG3, PAL, LOX2 and CYP86A1 genes that increased expression were selected for protein analysis. Due to the lack of protein structure of these genes in the milk thistle, modeling homology was performed for them. The results of molecular docking showed that the four proteins CYP86A1, LOX2, PAL and PXG3 bind to ligands HEM, 11O, ACT and LIG, respectively. HEM ligand was involved in production of secondary metabolites and dehydration tolerance, and HEM binding site remained conserved in various plants. CA ligands were involved in synthesis of cuticles and waxes. Overall, this study confirmed the importance of lipids in drought stress tolerance in milk thistle.

Potency of Titanium Dioxide Nanoparticles, Sodium Hydrogen Sulfide and Salicylic Acid in Ameliorating the Depressive Effects of Water Deficit on Periwinkle Ornamental Quality

In this study, the optimal concentration of sodium hydrosulfide (NaSH), salicylic acid (SA), and titanium dioxide nanoparticles (TiO2NPs), and their relative effectiveness on alleviating the adverse effects of water deficit on ornamental quality, were investigated in periwinkle. Plants were cultivated under three water deficit levels (80, 50, and 20% available water content) and received two foliar applications of TiO2NPs (0, 0.5 and 1 mM), NaSH (0.5 and 1 mM), or SA (1 and 2 mM). Water deficit deteriorated ornamental quality, amplified the risk of buckling (lower stem strength) and suppressed longevity. It decreased both light interception (leaf area) and carbon assimilation. Besides impaired hydration status, water-stressed plants underwent oxidative damage as indicated by reduced chlorophyll content, elevated membrane degradation, and lipid peroxidation. Spray treatments improved all traits, besides stem strength and proline content. Additionally, they enhanced carotenoid content and the activities of catalase and peroxidase. Their relative effectiveness (TiO2NPs > NaSH > SA) and optimal concentration (i.e., 0.5 mM (TiO2NPs, NaSH), and 1 mM (SA)) was independent of water deficit level. In conclusion, this study provides practices for improved ornamental quality and longevity independently of water availability, with their positive effect being stronger under irregular or limited water supply.

Biofilm forming rhizobacteria affect the physiological and biochemical responses of wheat to drought

Plant growth promoting rhizobacteria (PGPR) can attenuate the adverse effects of water deficit on plant growth. Since drought stress tolerance of bacteria has earlier been associated to biofilm formation, we aimed to investigate the role of bacterial biofilm formation in their PGPR activity upon drought stress. To this end, a biofilm-forming bacterial collection was isolated from the rhizospheres of native arid grassland plants, and characterized by their drought tolerance and evaluated on their plant growth promoting properties. Most bacterial strains formed biofilm in vitro. Most isolates were drought tolerant, produced auxins, showed 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity and solubilized mineral phosphate and potassium, but at considerably different levels. Greenhouse experiments with the most promising isolates, B1, B2 and B3, under three levels of water deficit and two wheat varieties led to an increased relative water content and increased harvest index at both moderate and severe water deficit. However, the bacteria did not affect these plant parameters upon regular watering. In addition, decreased hydrogen peroxide levels and increased glutathione S-transferase activity occurred under water deficit. Based on these results, we conclude that by improving root traits and antioxidant defensive system of wheat, arid grassland rhizospheric biofilm forming bacilli may promote plant growth under water scarcity.

Tracheidogram’s Classification as a New Potential Proxy in High-Resolution Dendroclimatic Reconstructions

Quantitative wood anatomy (QWA) is widely used to resolve a fundamental problem of tree responses to past, ongoing and forecasted climate changes. Potentially, QWA data can be considered as a new proxy source for long-term climate reconstruction with higher temporal resolution than traditional dendroclimatic data. In this paper, we considered a tracheidogram as a set of two interconnected variables describing the dynamics of seasonal variability in the radial cell size and cell wall thickness in conifer trees. We used 1386 cell profiles (tracheidograms) obtained for seven Scots pine (Pinus sylvestris) trees growing in the cold semiarid conditions of Southern Siberia over the years 1813–2018. We developed a “deviation tracheidogram” approach for adequately describing the traits of tree-ring formation in different climate conditions over a long-term time span. Based on the NbClust approach and K-means method, the deviation tracheidograms were reliably split into four clusters (classes) with clear bio-ecological interpretations (from the most favorable growth conditions to worse ones) over the years 1813–2018. It has been shown that the obtained classes of tracheidograms can be directly associated with different levels of water deficit, for both the current and previous growing seasons. The tracheidogram cluster reconstruction shows that the entire 19th century was characterized by considerable water deficit, which has not been revealed by the climate-sensitive tree-ring chronology of the study site. Therefore, the proposed research offers new perspectives for better understanding how tree radial growth responds to changing seasonal climate and a new independent proxy for developing long-term detailed climatic reconstructions through the detailed analysis of long-term archives of QWA data for different conifer species and various forest ecosystems in future research.

Specific features of the water regime of the genus Chaenomeles introduced plants in the steppe zone conditions

Sufficient water supply for plants is one of the most important conditions for their vital activity, since most of the biochemical reactions that regulate the plants physiological functions take place in the water environment. The plants adaptive capacity to the influence of a complex of environmental factors in field conditions is largely determined by the ability to maintain water balance, which can be characterized by various features. Among them, the transpiration intensity and the level of water deficit are the most important indicators that are related to the mechanisms of plant resistance to water or high-temperature stress. The aim of the work was to evaluate the introduction success of plants according to the markers of water availability in a new environment. The objects of the study were plants of the genus Chaenomeles, introduced in the Botanical Garden of Oles Honchar Dnipro National University: three natural species (Ch. japonica, Ch. speciosa, and Ch. cathayensis), as well as two hybrids (Ch. × superba and Ch. × californica). Species Ch. japonica naturally grows in humid areas with moderate temperatures, while species of Chinese origin Ch. speciosa and Ch. cathayensis are adapted to mountainous terrain with sharp temperature fluctuations. Water deficiency in the leaves of introduced plants was determined by saturating leaf cuttings with water; the intensity of transpiration was studied by the method of rapid weighing. Both indicators of the water regime in the leaves of introduced plants were measured under contrasting levels of moisture supply during the growing season in the steppe zone conditions: in the wet period, the dry period, and the period of moisture restoration. It was found that during the drought, the intensity of transpiration increased significantly (P ˂ 0.05) compared to the wet period in the leaves of all introduced Chaenomeles plants, the most (by 1.6–1.7 times) in Ch. japonica, Ch. speciosa and Ch. × superba, the least (by 1.3 times) in the leaves of Ch. × californica. Water deficit in the dry growing season in the leaves of all studied Chaenomeles plants increased significantly (P ˂ 0.05), the most in the leaves of Ch. catayensis (2.8 times compared to the wet period), the least in the leaves of Ch. spesiosa (in 2.0 times compared to the wet period). The level of water deficit in the leaves of both Chinese species was lower than that of Ch. japonica (18.85%). In the leaves of Ch. japonica, Ch. speciosa and Ch. × superba was the fastest recovery of the water balance after drought, as well as the most effective regulation of the transpiration intensity level with the onset of drought and during the recovery period. Introduced plants of the species Ch. japonica, Ch. speciosa and Ch. × superba turned out to be the most adapted to vegetation in the conditions of the steppe climate, which is characterized by periods of drought.

Response of yield, growth traits, and leaf nutrients of garden cress to deficit saline irrigation waters

abstract Food sustainability is continuously restricted by water shortage and poor water quality in water-scarce regions. In this study, a pot experiment was carried out under rain shelter conditions to quantify the impact of the different levels of water salinity on the yield, leaf nutrients, and growth traits of garden cress under different water-deficit levels. Twelve treatments included three water-deficit (WD) levels (I0, I1, and I2 indicating 100, 80, and 60% of field capacity, respectively) in combination with four saline irrigation water levels (IWS) (S1, S2, S3, and S4, indicating 0.38, 2, 4, and 8 dSm−1, respectively). Also, multiple linear regression analysis was performed to predict garden cress yield using WD, IWS, and soil salinity (ECe) parameters in different combinations. The results showed that yield, leaf area, stomata, chlorophyll content, leaf Ca2+, K+, K+/Na+, and Ca2+/Na+ markedly decreased under water deficit and water salinity interaction. The highest and lowest ECe values were observed at the I2S4 (8.67 dSm−1) and I0S1 (0.88 dSm−1) treatments. The highest yield was found at I0S1 (166.1 g pot−1), and it was 49.8% and 62.0% higher than I1S4 and I2S4 treatments. The developed models have R2 larger than 0.92, showing that they could provide a valuable tool for evaluating and estimating the garden cress productivity under different WD and IWS conditions. Finally, we conclude that WD (80% of FC or lower) combined with a higher IWS of 0.38 dSm−1 is not recommended for irrigating garden cress, which will cause considerable yield and commercial quality reduction of garden cress plants.

Stomatal conductance and transpiration in Allium sativum L. under water deficiency

The study aimed to verify the water stress indicators of garlic (Allium sativum L.) submitted to water deficit levels, simulating the effects of possible climatic changes. Considering that A. sativum is a crop known worldwide for its medicinal, culinary properties and applications in the ecological management of agricultural pests and, knowing that the planet is undergoing constant climatic changes, this study becomes essential to understand the influence of these changes on this species cultivation. The treatments were established with water conditions of 100, 75, 50, and 25% of the pot capacity (PC). According to the pot capacity, three bulbils were planted per pot (5 L) containing Plantmax® substrate, irrigated every two days. During the first and last week of the greenhouse treatments, the chlorophyll index was evaluated using a porometer with a seven-day interval between the analysis. The first analysis was performed in the first week of water stress and the last one in the last days of stress. Garlic plants showed sensitivity to water deficit, resulting in lower conductance and transpiration compared to treatments 50% and 75% water deficit, apparently without causing changes in production. In view of the results of this study, it is concluded that Allium sativum L. will not be totally harmed by the climate changes expected in the future according to atmospheric changes in the region of Laranjeiras do Sul.

Effects of increasing CO2 concentration and water deficit on photosynthetic performance and water use efficiency of typical green manure plants

Exploring the impacts of CO2 and soil water availability on the photosynthetic performance and water use efficiency of three green manure plants could provide theoretical basis for the adaptive management of grassland ecosystems under future climate change. An experiment was conducted in an artificial climate chamber with precisely controled CO2 concentrations of 400 (natural atmospheric) and 800 μmol·mol-1 (doubled), and four water treatments, 80% field water holding capacity (FC) (full irrigation control group), 55%-60% FC (mild water deficit), 35%-40% FC (moderate water deficit), <35% FC (severe water deficit) to investigate the impacts of increasing CO2 concentration and water deficit on chlorophyll content, gas exchange variables, and water use efficiency (WUE) of oilseed rape (Brassica napus), white clover (Trifolium repens), and alfalfa (Medicago sativa). The results showed that under the same CO2 concentration, when soil moisture was less than 40% FC, the chlorophyll content and gas exchange parameters of three plants were significantly decreased. The treatment of 55%-60% FC did not alter the total chlorophyll content of three species, but reduced the photosynthetic rate (Pn) and transpiration rate (Tr) of white clover and alfalfa by 6%-25% and did not affect their WUE. Compared with atmospheric CO2 concentration, the doubled CO2 concentration significantly decreased the Pn of oilseed rape by 21.5% under the full irrigation treatment, increased the Pn of three species under mild water deficit, increased the Pn of oilseed rape and alfalfa under moderate water deficit, but only improved the Pn of alfalfa under severe water deficit. The doubled CO2 concentration significantly increased WUE of white clover and alfalfa under all water deficit conditions, but only increased WUE of oilseed rape under mild water deficit. Increasing CO2 concentration and water deficit significantly interacted to affect Pn of three species and the WUE of oilseed rape. In summary, the three species differed in their responses to doubled atmospheric CO2 concentration and different levels of water deficit. Our results suggested that elevated CO2 concentration could improve the adverse effects of mild water deficit on photosynthetic performance and WUE of three species, but only improve the photosynthetic performance of alfalfa under severe water deficit.

Physiological and Morphological Characteristics of Drought-Stressed Chenopodium quinoa Willd, as Affected by Proline and Ascorbic Acid

ABSTRACT In order to study the effects of proline and ascorbic acid on some morphological and physiological characteristics of quinoa in response to drought stress, an experiment was conducted as split plot based on randomized complete block design with three replications, during two consecutive years. The main factor was drought stress at three levels, namely irrigation after 30, 60, and 100 mm evaporation (control, mild, and severe stress, respectively) from class A pan. The second factor included foliar application of proline sulfate at three levels (40, 80, and 120 mg/l), foliar application of ascorbic acid at three levels (50, 90, and 130 mg/l), and control (no spraying). Drought stress reduced seed yield, relative water content, and growth indices. Ascorbic acid and proline treatments at each level of drought stress improved the traits under study. In general, by increasing the concentration of proline and ascorbic acid at all water deficit levels (specially in condition of no drought stress), no specific trend was observed on the studied traits while the treatments with 120 mg ascorbic acid and 130 mg proline provided the optimal growth conditions under mild and severe stress conditions.

The combined effect of water deficit stress and TiO2 nanoparticles on cell membrane and antioxidant enzymes in Helianthus annuus L.

Nanotechnology has become one of the several approaches attempting to ameliorate the severe effect of drought on plant's production and to increase the plants tolerance against water deficit for the water economy. In this research, the effect of foliar application of TiO2, nanoparticles or ordinary TiO2, on Helianthus annuus subjected to different levels of water deficit was studied. Cell membrane injury increased by increasing the level of water deficit and TiO2 concentration, and both types of TiO2 affected the leaves in analogous manner. Ord-TiO2 increased H2O2 generation by 67–240% and lipid peroxidation by 4–67% in leaves. These increases were more than that induced by Nano-TiO2 and the effect was concentration dependent. Proline significantly increased in leaves by water deficit stress, reaching at 25% field capacity (FC) to more than fivefold compared to that in plants grown on full FC. Spraying plants with water significantly decreased the activities of enzymes in the water deficit stressed roots. The water deficit stress exerted the highest magnitude of effect on the changes of cell membrane injury, MDA, proline content, and activities of CAT and GPX. Nano-TiO2 was having the highest effect on contents of H2O2 and GPX activity. In roots, the level of water deficit causes highest effect on enzyme activities, but TiO2 influenced more on the changes of MDA and H2O2 contents. GPX activity increased by 283% in leaves of plants treated with 50 and 150 ppm Nano-TiO2, while increased by 170% in those treated with Ord-TiO2, but APX and CAT activities increased by 17–197%, in average, with Ord-TiO2. This study concluded that Nano-TiO2 didn’t ameliorate the effects of drought stress on H. annuus but additively increased the stress, so its use in nano-phytotechnology mustn’t be expanded without extensive studies.

Partial root zone drying method of irrigation: A review

AbstractWater availability has been a major constraint in crop production technology across the globe. The agricultural sector has been the largest consumer of fresh water for ages and accounts for about two‐thirds of the total fresh water used for human consumption. In the scenario of rapid population growth, the share of fresh water allocated to agriculture would get reduced to a great extent. Therefore, there is the ever‐increasing need to use the available water efficiently and precisely. It is a high priority to evolve new irrigation methods so that water use efficiency (WUE) can be maximized through optimum management of available irrigation water. Deficit irrigation (DI) is an optimization strategy that requires crops to intentionally endure a certain level of water deficit. This sometimes leads to a decrease in yield, however, with a significant increase in WUE. Partial root zone drying (PRD) is a modified version of DI, which has been practiced to improve WUE by controlling drought stress. In this method of irrigation, the spatial separation of dry and wet roots is maintained during the entire cropping season. The water stress developed in one part of the root zone generates chemical signals in the form of abscisic acid, which leads to partial closure of stomatal opening. Stomatal closure reduces the rate of transpiration, which in turn increases WUE. This paper is an effort to briefly discuss the concept of PRD and to review some important work carried out across the world.

Influence of drought stress on growth, biochemical changes and leaf gas exchange of strawberry (<i>Fragaria</i> × <i>ananassa</i> Duch.) in Indonesia

<abstract> <p>Drought stress is one of the challenges that can affect the growth and the quality of strawberry. The study aims to determine the growth, biochemical changes and leaf gas exchange of three strawberry cultivars under drought stress. This study was conducted in a glasshouse at Indonesian Citrus and Subtropical Fruits Research Institute, Indonesia, from July-November 2018. The experiment was arranged in a factorial randomized completely block design (RCBD) with three replications and four water deficit (WD) levels [100% field capacity (FC)/well-watered), 75% of FC (mild WD), 50% of FC (moderate WD), and 25% of FC (severe WD)] for three strawberry cultivars (Earlibrite, California and Sweet Charlie). The results showed that total chlorophyll and anthocyanin contents (p ≤ 0.05) were influenced by the interaction effects of cultivars and water deficit. Whereas other parameters such as plant growth, transpiration rate (<italic>E</italic>), net photosynthesis (<italic>A</italic>), stomatal conductance (<italic>gs</italic>), leaf relative water content (LRWC), flowers and fruits numbers, proline content, length, diameter, weight and total soluble solid (TSS) of fruit were affected by water deficit. <italic>A</italic> had positive significant correlation with plant height (r = 0.808), leaf area (r = 0.777), fruit length (r = 0.906), fruit diameter (r = 0.889) and fruit weight (r = 0.891). Based on the results, cultivars affected LRWC, and also number of flowers and fruits of the strawberry. This study showed that water deficit decreased plant growth, chlorophyll content, leaf gas exchange, leaf relative water content, length, diameter and weight of fruit but enhanced TSS, anthocyanin, MDA, and proline contents. Increased anthocyanin and proline contents are mechanisms for protecting plants against the effects of water stress. California strawberry had the highest numbers of flowers and fruits, and also anthocyanin content. Hence, this cultivar is recommended to be planted under drought stress conditions. Among all water stress treatments, 75% of FC had the best results to optimize water utilization on the strawberry plants.</p> </abstract>

Effects of arbuscular mycorrhizal inoculation on the growth, photosynthesis and antioxidant enzymatic activity of Euonymus maackii Rupr. under gradient water deficit levels.

The role of arbuscular mycorrhizal (AM) fungus (Rhizophagus intraradices) in the amelioration of the water deficit-mediated negative influence on the growth, photosynthesis, and antioxidant system in Euonymus maackii Rupr. was examined. E. maackii seedlings were subjected to 5 water deficit levels, soil water contents of 20%, 40%, 60%, 80% and 100% field capacity (FC), and 2 inoculation treatments, with and without AM inoculation. The water deficit increasingly limited the seedling height, biomass accumulation in shoots and roots, chlorophyll content, gas exchange and chlorophyll fluorescence parameters with an increasing water deficit level. In addition, water deficit stimulated the activities of antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), in both shoots and roots, except under 20% FC conditions. E. maackii seedlings under all water deficit conditions formed symbiosis well with AM fungi, which significantly ameliorated the drought-mediated negative effect, especially under 40% and 60% FC conditions. Under 40% to 80% FC conditions, AM formation improved seedling growth and photosynthesis by significantly enhancing the biomass accumulation, chlorophyll content and assimilation. Mycorrhizal seedlings showed better tolerance and less sensitivity to a water deficit, reflected in the lower SOD activities of shoots and roots and CAT activity of shoots under 40% and 60% FC conditions. Downregulation of the antioxidant system in mycorrhizal seedlings suggested better maintenance of redox homeostasis and protection of metabolism, including biomass accumulation and assimilation. All the results advocated the positive role of R. intraradices inoculation in E. maackii against a water deficit, especially under 40% FC, which suggested the distinct AM performance in drought tolerance and the potential role of the combination of E. maackii-AM fungi in ecological restoration in arid regions.

The effect of water deficit and livestock stocking density on soil organic carbon stocks in Namibia

Livestock integrated land use systems are considered as viable options for enhancing soil organic carbon (SOC) sequestration in a changing climate. This study assessed the influence of water deficit and livestock stocking density on soil carbon stocks. A total of 101 matching data were extracted from map layers of water deficit and livestock stocking density for C storage in Arenosols of Omusati and Otjozondjupa regions of Namibia. Maps for water deficit and livestock stocking density were obtained from national databases. The SOC data were arranged into four treatment combinations represented by two levels of water deficit and two levels of livestock stocking density. Linear mixed models (LMM) were then used to evaluate differences in SOC stocks in response to livestock stocking density and water deficit. Results showed that there was a significant interaction (p = 0.013) between the effects of livestock stocking density and water deficit on C-stocks. In conditions where the water deficit was small, the SOC stock was larger under more intensive grazing. Whilst in conditions where water deficit was large, the SOC stock was larger under less intensive grazing. Furthermore, the difference between SOC stock at large and small water deficits was larger under more intensive grazing. This shows that the impacts of a changing climate, and changes in the intensity of grazing must be considered together to predict effects on the SOC stock.