Intense Water Deficit Research Articles

Water Deficit Severity during the Preceding Year Determines Plant Tolerance to Subsequent Year Drought Stress Challenges: A Case Study in Damask Rose

Damask rose is an important essential oil crop. In the present study, plants were subjected to three different water deficit levels (70, 40, and 10% available water content) for two periods (June–October). Plant phenology, growth, essential oil yield, gas exchange features, membrane stability and major antioxidant defense elements were monitored across two years. Soil water deficit was related to quicker completion of the growth cycle (up to 7.4 d), and smaller plants (up to 49.7%). Under these conditions, biomass accumulation was jointly constrained by decreased leaf area, chlorophyll content, CO2 intake, and photosynthetic efficiency (up to 82.8, 56.9, 27.3 and 68.2%, respectively). The decrease in CO2 intake was driven by a reduction in stomatal conductance (up to 41.2%), while the decrease in leaf area was mediated by reductions in both number of leaves, and individual leaf area (up to 54.3, and 64.0%, respectively). Although the reactive oxygen species scavenging system was activated (i.e., proline accumulation, and enhanced activity of three antioxidant enzymes) by water deficit, oxidative stress symptoms were still apparent. These effects were amplified, as soil water deficit became more intense. Notably, the adverse effects of water deficit were generally less pronounced when plants had been exposed to water severity during the preceding year. Therefore, exposure to water deficit elicited plant tolerance to future exposure. This phenotypic response was further dependent on the water deficit level. At more intense soil water deficit across the preceding year, plants were less vulnerable to water deficit during the subsequent one. Therefore, our results reveal a direct link between water deficit severity and plant tolerance to future water stress challenges, providing for the first time evidence for stress memory in damask rose.

What are the impacts of water deficit, cultivars, and agricultural years on the dynamics of nutrient uptake by common bean? Part I: n, P, and K

Knowing the effect of water deficit intensity on the nutrient uptake dynamics by common bean cultivars with contrasting growth habits in different years is necessary to appraise and recommend more specific fertilization management practices. A field study was carried out in the Southeast of Brazil for two years aiming to explain and compare the accumulation and extraction of the macronutrients nitrogen (N), phosphorus (P), and potassium (K) from two common bean cultivars with contrasting growth habits as a function of water deficit severity. The common bean cultivars IAC Imperador and IPR Campos Gerais, with determinate and indeterminate growth habits, respectively, were evaluated. Both cultivars were submitted to three irrigation management practices: severe water deficit (54% of the crop evapotranspiration – ETc), moderate water deficit (77% of ETc), and no water deficit (100% of ETc). Overall, the severe water deficit reduced N, P, and K accumulation in the common bean cultivars by 26, 37, and 23%, respectively. Under no water deficit, IPR Campos Gerais showed higher accumulation of biomass and nutrients N (27%) and P (42%) compared to IAC Imperador, in addition to higher interannual variability in the accumulation of nutrients. The maximum daily demand for nutrients N, P, and K of IAC Imperador was anticipated in 9, 13 and 11 days, respectively, compared to IPR Campos Gerais. Irrigation management, cultivar, and climate of the agricultural year are important factors in decision-making for the most adequate establishment of fertilization with N, P, and K in common bean.

Drought resistance of nine maize cultivars released from the 1970s through the 2010s in China

ProblemWater scarcity has become a limiting factor for increasing crop production. Yield losses due to drought stress can best be resolved by breeding new, drought-tolerant cultivars, however, the genetic gains in drought resistance of different maize cultivars especially under precise water control conditions were not systematically studied.The objectives of this study were to assess 1) the change in yield and WUE of different cultivars from the 1970s through the 2010s under precise water control conditions and 2) find out the main factors affecting the yield and WUE change of different cultivars. MethodsWe selected nine hybrids from different eras for a detailed field study under three different water treatments (full irrigation, moderate drought, and intense drought) in a rainout shelter at Hengshui (115°40′E, 37°44′N) in southern Hebei province in 2018 and 2019. We compared the grain yield and water use efficiency (WUE) of different cultivars from the 1970s through the 2010s under drought-stress (moderate drought and intense drought) and fully-irrigated conditions. ResultsThe maize yield and WUE showed a significant linear increase with the year of release. The average yield gains were 111, 113.4 and 121.3 kg ha−1yr−1 under fully-irrigated, moderate and intense drought conditions while the WUE gains were 0.31, 0.38 and 0.72 kg ha−1 mm−1 yr−1 respectively. The yield reduction ratio showed a significant linear decrease from the 1970 s through the 2010s under both moderate water deficit and intense water deficit which were 0.51 % and 0.99 % yr−1, indicating that modern cultivars had better drought resistance than older ones. With increased water stress, the yield gap and yield reduction ratio between full irrigation and drought treatments (moderate drought and intense drought) increased significantly. The significant increase in the number of ears per hectare and the number of kernels per ear was the main reason for maize yield increase with the year of release from 1970s to 2010s under drought treatments. Under drought stress, the uniformity of yield component decreased significantly compared to the fully-irrigated treatment. In addition, an overly large leaf area was not conducive to drought resistance. ConclusionsModern cultivars had better drought resistance than older ones. Selecting hybrids with higher uniformity and smaller leaf area was beneficial to improve the maize drought resistance. ImplicationsThe results of this study will be beneficial for the breeding and selecting drought-resistant cultivars.

Phenology and South American leaf blight of polyclonal seedlings population of natural rubber trees in Colombia

The phenological development of polyclonal rubber plantations has been little explored, although they present adaptive potential to specific biotic and abiotic conditions. Between 2016 and 2021, rubber tree seedlings were evaluated for leaf ontogeny, leaf area index (LAI), and reproductive phenology (flowers and fruits). The climatic conditions were correlated with the foliar and reproductive rubber phenology and the incidence and severity of the South American leaf blight (SALB). The tree phenology showed a relationship between defoliation-refoliation with the water deficit intensity and high temperatures. The development of the trees in a polyclonal plantation was heterogeneous, and the defoliation-refoliation phases were extended over time. A higher SALB severity was associated with higher relative humidity and radiation periods, reducing the leaf area (atypical defoliation) and changing flowering and fruiting seasonality. The intensity and duration of climatic factors, particularly water deficit, are important for determining phenological processes and fungal diseases such as SALB, which serves as a tool to build management strategies both in seed production and obtaining latex in scenarios of climate change.

Water deficit before veraison is crucial in regulating berry VOCs concentration in Sangiovese grapevines.

The impact of water deficit on volatile organic compounds (VOCs) responsible for grape aroma remains quite unclear. The aim of this study was to evaluate the effect of different timing and intensity of water deficit on berry VOCs and on their biosynthetic pathways. Fully irrigated control vines were compared with the following treatments: i) two different levels of water deficit from berry pea-size through veraison, ii) one level of water deficit during the lag-phase, and iii) two different levels of water deficit from veraison through harvest. At harvest, total VOC concentrations were higher in berries of water stressed vines from berry pea size through veraison or during the lag phase, whereas post-veraison water deficit determined similar concentrations as control. This pattern was even more pronounced for the glycosylated fraction and was also observed for single compounds, mainly monoterpenes and C13-norisoprenoids. On the other hand, free VOCs were higher in berries from lag phase or post-veraison stressed vines. The significant glycosylated and free VOCs increment measured after the short water stress limited to the lag phase highlight the pivotal role played by this stage in berry aroma compound biosynthesis modulation. The severity of water stress before veraison was also important, since glycosylated VOCs showed a positive correlation with the pre-veraison daily water stress integral. The RNA-seq analysis showed a wide regulation induced by irrigation regimes on terpenes and carotenoids biosynthetic pathways. The terpene synthases and glycosyltransferases as well as genes of the network of transcription factors were upregulated, especially in berries from pre-veraison stressed vines. Since the timing and intensity of water deficit contribute to regulate berry VOCs, irrigation management can be used to achieve high-quality grapes while saving water.

Exploiting multiple hydrologic forecasts to inform real-time reservoir operation for drought mitigation

To timely prompt anticipatory operations and relieve prolonged droughts effectively, multiple hydrological forecasts that provide thorough information about future streamflow need to be employed. However, it is challenging to integrate multiple forecasts in reservoir optimization and obtain a proper trading-off between current and future water supply benefits. This study proposes a novel Model Predictive Control (MPC) that can not only utilize the streamflow forecast but also utilize other two categorical forecasts, including the regime state forecast to capture the long-term persistence of the streamflow process and the annual streamflow volume state forecast. In the novel MPC, a discount factor depending on the annual streamflow volume state forecast weighs up the current deficit cost decided by the streamflow forecast and the future cost function determined by the regime state forecast. Taking the Biliuhe Reservoir in China as a case study, the value of each forecast in drought mitigation is evaluated. Results show that with an appropriate discount factor, using seasonal streamflow forecast can relieve intense deficits for extreme droughts and avoid unnecessary intense limitations for slight droughts. Utilizing the annual streamflow volume state forecast contributes to guaranteeing a reliable water supply. And employing the regime state forecast relieves the intensity of severe water deficit. By incorporating these hydrological forecasts, a 31.86% performance gain can be obtained with only a 5.03% reliability decrease compared to the baseline Stochastic Dynamic Programming informed by no forecast information. Nevertheless, forecast value is beset by forecast uncertainty. For streamflow forecast, forecast value decreases with increasing forecast uncertainty. But for the other two categorical forecasts, their forecast value depends on not only the forecast accuracy but also the hydrologic conditions and forecast bias.

Mechanical Intervention in Compacted No-Till Soil in Southern Brazil: Soil Physical Quality and Maize Yield

The intense and successive use of mechanization in modern cropping systems has increased soil compaction under no-till areas. In this study, we aimed to assess the performance of a fixed shank coupled with a seeder for the mitigation of soil compaction induced by machinery traffic as an efficient alternative to replacing the chiseling and subsoiling operations in no-till areas. We evaluated a long-term experiment conducted in clay loam (Rhodic Haplustox) soil in southern Brazil. The experiment was conducted under a randomized block design, whose treatments consisted of three wheel-traffic intensities: 0 wheel-traffic (0 WT), 14 wheel-traffic (14 WT), and 28 wheel-traffic (28 WT), combined with four soil tillage mechanical interventions under a no-till field: no-till (NT), no-till with a fixed shank (NT + FS), soil chiseling (SC), and soil subsoiling (SS). The soil physical attributes evaluated were the soil penetration resistance (SPR), macroporosity (MaP), microporosity (MiP), total porosity (TP), bulk density (BD), field-saturated hydraulic conductivity (Kfs), S index, and plant-available water capacity (PAWC). In addition, three critical soil physical functions were evaluated by using a soil physical quality index (SPQI). The results showed that SPR was sensitive to soil compaction and captured differences among the mechanical intervention methods. Machinery traffic caused soil compaction, increasing SPR and reducing PAWC. Soil chiseling and subsoiling promoted lower BD, a higher TP, MaP, Kfs, and higher S index at the 0.05–0.15 m soil layer. Based on the SPQI, no changes were detected in the soil physical functions between NT and NT + FS. On the other hand, SC and SS enhanced soil physical functioning by 10%. We concluded that a 15-cm deep fixed shank could not mitigate the soil compaction induced by machinery traffic at the seeder operation. Therefore, this method is less effective in improving the soil’s physical environment than chiseling and subsoiling operations. Finally, we encourage monitoring the persistence of these benefits on the soil over the subsequent crop seasons and in years with an intense water deficit along with the crop cycle.

Regulatory mechanisms behind the phenotypic plasticity associated with Setaria italica water deficit tolerance.

Drought is one of the main environmental stresses that negatively impacts vegetative and reproductive yield. Water deficit responses are determined by the duration and intensity of the stress, which, together with plant genotype, will define the chances of plant survival. The metabolic adjustments in response to water deficit are complex and involve gene expression modulation regulated by DNA-binding proteins and epigenetic modifications. This last mechanism may also regulate the activity of transposable elements, which in turn impact the expression of nearby loci. Setaria italica plants submitted to five water deficit regimes were analyzed through a phenotypical approach, including growth, physiological, RNA-seq and sRNA-seq analyses. The results showed a progressive reduction in yield as a function of water deficit intensity associated with signaling pathway modulation and metabolic adjustments. We identified a group of loci that were consistently associated with drought responses, some of which were related to water deficit perception, signaling and regulation. Finally, an analysis of the transcriptome and sRNAome allowed us to identify genes putatively regulated by TE- and sRNA-related mechanisms and an intriguing positive correlation between transcript levels and sRNA accumulation in gene body regions. These findings shed light on the processes that allow S. italica to overcome drought and survive under water restrictive conditions.

The Improvement of Maize (Zea mays L.) for Drought Stress Tolerance

Maize is one of the important cereals in the world after rice and wheat. It is grown for grain as well as fodder in tropical, sub-tropical and temperate regions of the World. The reduction of maize productivity under drought stress conditions depends on different factors such as plant development stage, drought intensity and duration of water deficit, and varietal sensitivity to drought stress. Drought stress is one of the major constraints to agriculture where limited water availability for crop irrigation causes a reduction in carbon fixation by the photosynthetic apparatus that result in net yield losses. Plant breeders desire novel and more accurate tools to fast-track breeding programs required for the increasing demands of food and fodder because farmers are facing a changing climate in which drought stress has major impacts on crop damages globally. Crop loss, because of drought stress, has a huge impact on agriculture industry and the economy. Therefore, to prevent economic loss and to make the crop plants more tolerant to drought stress, a variety of approaches such as conventional breeding and molecular/ genetic engineering are being practiced. Keywords: Genetic engineering, Conventional breeding, Molecular assisted selection, Drought and Stress DOI: 10.7176/JBAH/11-17-04 Publication date: September 30 th 2021

Effects of ectomycorrhizal fungi (Suillus variegatus) on the growth, hydraulic function, and non-structural carbohydrates of Pinus tabulaeformis under drought stress

BackgroundA better understanding of non-structural carbohydrate (NSC) dynamics in trees under drought stress is critical to elucidate the mechanisms underlying forest decline and tree mortality from extended periods of drought. This study aimed to assess the contribution of ectomycorrhizal (ECM) fungus (Suillus variegatus) to hydraulic function and NSC in roots, stems, and leaves of Pinus tabulaeformis subjected to different water deficit intensity. We performed a continuous controlled drought pot experiment from July 10 to September 10, 2019 using P. tabulaeformis seedlings under 80, 40, and 20% of the field moisture capacity that represented the absence of non-drought, moderate drought, and severe drought stress, respectively.ResultsResults indicated that S. variegatus decreased the mortality rate and increased height, root biomass, and leaf biomass of P. tabulaeformis seedlings under moderate and severe drought stress. Meanwhile, the photosynthetic rates, stomatal conductance, and transpiration rates of P. tabulaeformis were significantly increased after S. variegatus inoculation. Moreover, the inoculation of S. variegatus also significantly increased the NSC concentrations of all seedling tissues, enhanced the soluble sugars content, and increased the ratios of soluble sugars to starch on all tissues under severe drought. Overall, the inoculation of S. variegatus has great potential for improving the hydraulic function, increasing the NSC storage, and improving the growth of P. tabulaeformis under severe drought.ConclusionsTherefore, the S. variegatus can be used as a potential application strain for ecological restoration on arid regions of the Loess Plateau, especially in the P. tabulaeformis woodlands.

Genetically modified maize hybrids and delayed sowing reduced drought effects across a rainfall gradient in temperate Argentina.

Before the introduction of genetically modified insect-tolerant maize (Zea mays L.) in 1997, most of the production of this staple in Argentina was concentrated in humid and sub-humid temperate regions. Early spring sowings minimized the risk of water deficit around flowering and yield reduction due to pests. Use of genetically modified maize allowed optimization of sowing dates to synchronize critical periods for kernel set determination with the times of the year when water deficits are less likely, reducing large interannual variations in grain yield. This change in sowing date did not start until 2009, after the occurrence of two successive dry phases of the El Niño-Southern Oscillation phenomenon. The area of land cropped to maize in Argentina has expanded dramatically since then, particularly beyond the humid areas. Currently, maize is sown in an almost 50%/50% distribution between early and late sowings, including double cropping. Changes in agronomic practices such as sowing date and production area can lead to changes in the timing and intensity of water deficits along the maize growth cycle. This review provides an overview of new patterns of water deficit across humid, sub-humid, and semi-arid mid-latitude environments of Argentina, and their effects on grain yield and yield components.

Effects of Water Deficits on Prosopis tamarugo Growth, Water Status and Stomata Functioning.

The effect of water deficit on growth, water status and stomatal functioning of Prosopis tamarugo was investigated under controlled water conditions. The study was done at the Antumapu Experiment Station of the University of Chile. Three levels of water stress were tested: (i) well-watered (WW), (ii) medium stress intensity (low-watered (LW)) and (iii) intense stress (non-watered (NW)), with 10 replicates each level. All growth parameters evaluated, such as twig growth, specific leaf area and apical dominance index, were significantly decreased under water deficit. Tamarugo twig growth decreased along with twig water potential. The stomatal conductance and CO2 assimilation decreased significantly under the water deficit condition. Tamarugo maintained a high stomatal conductance at low leaf water potential. In addition, tamarugo reduced its leaf area as a strategy to diminish the water demand. These results suggest that, despite a significant decrease in water status, tamarugo can maintain its growth at low leaf water potential and can tolerate intense water deficit due to a partial stomatal closing strategy that allows the sustaining of CO2 assimilation in the condition of reduced water availability.

Exploring the relationship between stand growth, structure and growth dominance in Eucalyptus monoclonal plantations across a continent-wide environmental gradient in Brazil

Stand structure can have a considerable influence on forest growth and productivity. A stand’s response to factors like temperature, precipitation, vapor pressure deficit and different soil characteristics may result not only from the mean change in tree responses (e.g. growth decrease or increase), but may also depend on how individual tree responses vary in relation to their size and how they cope with competition. There may be a large growth imbalance among trees as a function of their size, which is referred to as growth dominance. That is, a change in a factor may have different impacts on stand growth depending on stand structure and how growth is distributed. Thus, using an experimental platform spanning tropical Brazil, we explored the relationship between growth dominance and stand growth, and whether this relationship changes across a wide climatic gradient, represented by soil water deficit. We found a predominance of negative growth dominance during the early phase of stand development which increased until dominance became positive, after about 30 months, and kept increasing afterwards. Increasing soil water deficit slowed the increase in growth dominance throughout time. The intensification of growth dominance (either positive or negative) was associated with decreasing stand growth. Increasing soil water deficit decreased the negative effect of growth dominance on increment in absolute terms, but we showed that, at the end of a 5-year rotation, increasing growth dominance at a site with more intense water deficit led to a greater growth loss in relative terms than at a site with milder water deficit. For example, the estimated difference in increment between a stand with a low growth dominance of 0.05 and a stand with a high growth dominance of 0.20 at the end of a 60–month rotation at a site with an accumulated water deficit of −200 mm was about 28 m3 ha−1 year−1, which is equivalent to a 39% decrease in relative terms. This same GDC difference under a water stress of −4000 mm resulted in a decrease in increment of approximately 18 m3 ha−1 year−1, or 48% in relative terms.

Effects of multiple climate change factors on exoenzyme activities and CO2 efflux in a tropical grassland

Climate change is expected to affect rainfall dynamics and the global average temperature. Here, we evaluated the effects of those changes, the intense water deficit and warming (+2 °C), on a tropical grassland soil. We tested the correlation between soil extracellular enzyme activities (EEA) and soil respiration (CO2 efflux) and temperature and soil water content (SWC). A climate change simulation was performed in a field experiment using a temperature free-air-controlled enhancement facility. SWC was the main driver of changes in EEA. The most affected enzymes were β-glucosidase, xylanase and phosphatase. As SWC declined, the potential activity of β-glucosidase and xylanase decreased, while the activity of phosphatase and CO2 efflux increased (P < 0.01). Thus, intense drought periods are likely to have a greater influence on the rates of decomposition and mineralization in the evaluated soil than is the 2 °C increase in mean temperature.

Daily osmotic adjustments in stem may be good predictors of water stress intensity in poplar

Drought events impair the carbon and water balances in plants. Climate changes highlight the importance to understand the limits of woody species to reallocate carbon in different processes and the mechanisms driving the osmotic adjustments during the day under stress. In this frame, the aim of this work was to investigate the plant capability to shift energy among competing sinks and preserve the osmotic balance during the day under severe short periods of water deficit. The role of carbohydrates as osmolytes as well as energy sources was investigated in poplar plants. Results highlighted that during water deficit soluble sugars, derived both from the new synthetised carbon and starch degradation, were principally convoyed in the bark. This increase in carbohydrates allowed the maintenance of a water reserve used during the day to prevent a water decrease within the xylem. The decrease of xylem sap osmotic potential during the night, driven by an increase of K, Ca, and fructose (+0.46, 0.52, and 0.26 mg ml−1 in water limited plants after 8 days of withholding water, respectively), probably further attracted water into the xylem. This response mechanism increased at higher water deficit intensity. The little variations in carbohydrates and mineral elements within the leaves highlighted the main role of sinks rather than sources in the early response to water deficit.

A continuum of stomatal responses to water deficits among 17 wine grape cultivars (Vitis vinifera).

Vitis vinifera L. cultivars have been previously classified as isohydric, near-isohydric, anisohydric or isohydrodynamic, depending on the study. To test the hypothesis that V. vinifera cultivars' stomatal behaviour can be separated into distinct classes, 17 cultivars grown in a replicated field trial were subjected to three irrigation treatments to manipulate vine water status across multiple years. Predawn (ΨPD) and midday (Ψl) leaf water potential and midday stomatal conductance (gs) were measured regularly throughout several seasons. The relationship of gs to Ψl was best modelled as a sigmoidal function and maximum stomatal conductance (gmax), water status at the onset of stomatal closure (Ψl95), sensitivity of closure (gsensitivity) and water status at the end of closure (Ψl25) were compared. There were no significant differences in gmax among cultivars. Cultivar-specific responses of gs to Ψl were broadly distributed along a continuum based on the relationship between Ψl95 and gsensitivity. Season-long cultivar mean Ψl values were positively related to Ψl25. In general, cultivars responded similarly to one another at high and low water status, but their stomatal behaviour differed at moderate water deficits. The results show that V. vinifera cultivars possess both iso- and anisohydric stomatal behaviours that depend on the intensity of water deficits, and call into question previous classifications assuming a single behaviour.

Abscisic Acid Coordinates Dose-Dependent Developmental and Hydraulic Responses of Roots to Water Deficit.

Root water uptake is influenced by root system architecture, which is determined by root growth and branching and the hydraulics of root cells and tissues. The phytohormone abscisic acid (ABA) plays a major role in the adaptation of plants to water deficit (WD). Here we addressed at the whole-root level in Arabidopsis (Arabidopsis thaliana) the regulatory role of ABA in mechanisms that determine root hydraulic architecture. Root system architecture and root hydraulic conductivity (Lpr) were analyzed in hydroponically grown plants subjected to varying degrees of WD induced by various polyethylene glycol (PEG) concentrations. The majority of root traits investigated, including first- and second-order lateral root production and elongation and whole-root hydraulics, had a bell-shaped dependency on WD, displaying stimulation under mild WD conditions (25 g PEG L-1) and repression under more severe conditions. These traits also showed a bell-shaped dependency on exogenous ABA, and their regulation by WD was attenuated in genotypes altered in ABA biosynthesis and response. Thus, we propose that ABA acts as a coordinator and an integrator of most root responses to mild and moderate WD, whereas responses to strong WD (150 g PEG L-1) are largely ABA independent. We also found that roots exhibit different growth responses to both WD and ABA depending on their rank and age. Taken together, our results give further insights into the coordinated water acquisition strategies of roots deployed in relation to WD intensity.

Automated Measurement and Control of Germination Paper Water Content.

Germination paper (GP) is used as a growth substrate in plant development studies. Current studies bear two limitations: (1) The actual GP water content and variations in GP water content are neglected. (2) Existing irrigation methods either maintain the GP water content at fully sufficient or at a constant deficit. Variation of the intensity of water deficit over time for plants grown on GP is not directly achievable using these methods. In this contribution, a new measurement and control approach was presented. As a first step, a more precise measurement of water content was realized by employing the discharging process of capacitors to determine the electrical resistance of GP, which is related to the water content. A Kalman filter using an evapotranspiration model in combination with experimental data was used to refine the measurements, serving as the input for a model predictive controller (MPC). The MPC was used to improve the dynamics of the irrigation amount to more precisely achieve the required water content for regulated water uptake in plant studies. This is important in studies involving deficit irrigation. The novel method described was capable of increasing the accuracy of GP water content control. As a first step, the measurement system achieved an improved accuracy of 0.22 g/g. The application of a MPC for water content control based on the improved measurement results in an overall control accuracy was 0.09 g/g. This method offers a new approach, allowing the use of GP for studies with varying water content. This addressed the limitations of existing plant growth studies and allowed the prospection of dependencies between dynamic water deficit and plant development using GP as a growth substrate for research studies.

Simulated Assessment of Summer Maize Drought Loss Sensitivity in Huaibei Plain, China

In an agricultural drought risk system, crop drought loss sensitivity evaluation is a fundamental link for quantitative agricultural drought loss risk assessment. Summer maize growth processes under various drought patterns were simulated using the Cropping System Model (CSM)-CERES-maize, which was calibrated and validated based on pit experiments conducted in the Huaibei Plain during 2016 and 2017 seasons. Then S-shaped maize drought loss sensitivity curve was built for fitting the relationship between drought hazard index intensity at a given stage and the corresponding dry matter accumulation and grain yield loss rate, respectively. Drought stress reduced summer maize evapotranspiration, dry matter, and yield accumulation, and the reductions increased with the drought intensity at each stage. Moreover, the losses caused by drought at different stages were significantly different. When maize plants were exposed to a severe water deficit at the jointing stage, the dry matter and grain yield formation were greatly affected. Therefore, maize growth was more sensitive to drought stress at the jointing stage when the stress was serious. Furthermore, when plants encountered a relatively slight drought during the seedling or jointing stage, which represented as a lower soil water deficit intensity, the grain yield loss rates approached the maximum for the sensitivity curves of these two stages. Therefore, summer maize tolerance to water deficit at the seedling and jointing stages were weak, and yield formation was more sensitive to water deficit during these two stages when the deficit was relatively slight.

Quantitative assessment of soybean drought loss sensitivity at different growth stages based on S-shaped damage curve

Crop drought loss sensitivity assessment is fundamental for managing agricultural drought risk. Potted soybean water deficit experiments with different irrigation treatments during two seasons (2015 and 2016) were conducted in China’s Huaibei Plain. S-shaped soybean drought loss sensitivity curves at four growth periods were established, and the sensitivity of seed formation to water deficit during different stages was quantitatively compared. The results indicated that the negative effects of water deficit during the flowering-podding and seed filling stages on yield formation were greater than those during the branching and seedling stages. Similarly, aboveground biomass and 1000 seed weight both reached the minimum when soybeans encountered a severe water deficit during the seed filling stage. According to the parameters of the sensitivity curve, the seed yield loss was the greatest when soybeans experienced severe drought stress during the flowering-podding stage. In addition, soybean tolerance to drought during the seedling stage was relatively weak. Moreover, the sensitivity at each growth period varied with water deficit intensity. If there was a mild water defict, soybean yield formation was more sensitive to the deficit when it occurred during the seedling stage. However, if the deficit was relatively serious, yield formation became more sensitive when it happened during the flowering-podding stage. Therefore, it is crucial to strictly control the water deficit intensity during the seedling stage and ensure an adequate water supply during the reproductive growth period, especially during the flowering and pod-enlargement stage, for guaranteeing a high soybean yield.