Prolonged Water Deficit Research Articles

Screening for Suitable Melatonin Application Scheme to Modulate Drought Stress in Bulgarian Wheat

Drought occupies a dominant share among the environmental factors that directly cause significant economic losses. Wheat is one of the most important crops for humankind, and although it tolerates drought to a certain extent, prolonged water deficit provokes a number of unfavourable alterations in plants, which lead to a significant decrease in productivity. Because of the broadening climate changes, the search for ecological biostimulants as an innovative approach to reduce the harmful effects of drought is gaining more popularity in modern agriculture. Melatonin is a natural product of plant metabolism with growth-regulating properties – it is non-toxic and is safe for the environment. We aimed to investigate the possibilities to modulate the negative effects of drought through application of melatonin using a comparative analysis of the physiological reactions of young wheat seedlings. We studied the effects of melatonin applied before drought on the physiological responses of two Bulgarian wheat cultivars grown as a soil culture. Different concentrations of melatonin ranging from 5 to 500 μM were tested and 75 μM was selected as a promising one. Additionally, we tested the method of application of melatonin – leaf spray or root supplement. Based on the content of selected stress markers we could make a conclusion that leaf spraying of plants before stress had some attenuating effect on the negative consequences of drought, but one dose of root application appeared to be more effective. Abbreviations: MDA – malondialdehyde, Mel – melatonin, ROS – reactive oxygen species

Xylem cell size regulation is a key adaptive response to water deficit in Eucalyptus grandis.

Future climatic scenarios forecast increasingly frequent droughts that will pose substantial consequences on tree mortality. In light of this, drought-tolerant eucalypts have been propagated; however, the severity of these conditions will invoke adaptive responses, impacting the commercially valuable wood properties. To determine what mechanisms govern the wood anatomical adaptive response, highly controlled drought experiments were conducted in Eucalyptus grandis W. Hill ex Maiden, with the tree physiology and transcriptome closely monitored. In response to water deficit, E. grandis displays an isohydric stomatal response to conserve water and enable stem growth to continue, albeit at a reduced rate. Maintaining gaseous exchange is likely a critical short-term response that drives the formation of hydraulically safer xylem. For instance, the development of significantly smaller fibers and vessels was found to increase cellular density, thereby promoting drought tolerance through improved functional redundancy, as well as implosion and cavitation resistance. The transcriptome was explored to identify the molecular mechanisms responsible for controlling xylem cell size during prolonged water deficit. Downregulation of genes associated with cell wall remodeling and the biosynthesis of cellulose, hemicellulose and pectin appeared to coincide with a reduction in cellular enlargement during drought. Furthermore, transcript levels of NAC and MYB transcription factors, vital for cell wall component biosynthesis, were reduced, while those linked to lignification increased. The upregulation of EgCAD and various peroxidases under water deficit did not correlate with an increased lignin composition. However, with the elevated cellular density, a higher lignin content per xylem cross-sectional area was observed, potentially enhancing hydraulic safety. These results support the requirement for higher density, drought-adapted wood as a long-term adaptive response in E. grandis, which is largely influenced by the isohydric stomatal response coupled with cellular expansion-related molecular processes.

Morpho-physiological adaptations to drought stress in nitrogen-fixing and non-nitrogen-fixing plants

Drought profoundly affects the morpho-physiological responses of desert plants in dryland. To scrutinize the morpho-physiological responses of nitrogen (N)-fixing legumes (Ammopiptanthus mongolicus, Caragana korshinskii), N-fixing non-legumes (Elaeagnus angustifolia, Hippophae rhamnoides), and non-N-fixing plants (Nitraria tangutorum, Haloxylon ammodendron) under varied drought stress levels (75%, 50%, 25% and 5% of soil water holding capacity), a pot experiment was conducted in greenhouse. Following prolonged water deficit, carbon (C) and N stoichiometry, metabolic rates, plant growth, and biomass distribution of unstressed and stressed plants were recorded. Intensified drought significantly reduced stem, root and whole-plant biomass, with no significant changes observed in leaf dry-fresh mass ratio, specific leaf area, intrinsic water use efficiency and root to shoot ratio. However, other traits were impacted differently, reflecting distinct adaptive strategies to drought among three plant functional types (PFTs). Patterns of trait-soil water content (SWC) relationships varied across different PFTs, with N-fixing non-legumes followed by N-fixing legumes displayed greater sensitivity to SWC variations than non-N-fixing plants. This resulted in a shift from a stronger trait-SWC relationship in N-fixing non-legumes and N-fixing legumes to a less correlated relationship in non-N-fixing plants. The diverse responses to drought among PFTs suggest a shift from N limitation to water limitation as SWC decreases.

Recovery of root hydraulic conductance and xylem vessel diameter following prolonged water deficit of maize

AbstractTo sustain crop growth following soil water deficit, it is essential to have rapid recovery of leaf gas exchange. One basis for rapid recovery would be the rapid return of root hydraulic conductance to predrought levels to support water transport to the plant shoot. In this study, transpiration and root hydraulic conductance were measured over a 9‐day recovery period following an initial water‐deficit treatment of three maize (Zea mays L.) cultivars. In addition, xylem vessel diameter was measured during the recovery period at different positions from the root tip. The initiation of recovery in the transpiration rate occurred in all three cultivars within 3 days after watering, although the root conductance and transpiration rate of one cultivar were much lower than the other two cultivars. Root conductance and vessel diameter increased more slowly than the recovery of transpiration. There was an indication that transpiration could have been limited by root hydraulic conductance only when its values were low during recovery. The relationship between hydraulic conductance and vessel diameter did not, however, indicate a Poiseuille's law relationship between the two variables. Overall, cultivar variability in recovery from water deficit of the transpiration rate and root hydraulic conductance indicates that the selection for rapid recovery of leaf gas exchange following water deficit could be an important component of genotype selection in maize breeding programs.

Combined effects of mixing ratios and tree size: how do mixed forests respond to climate and drought events?

Although the relationship between biodiversity and ecosystem functionality (BEF) has been studied comprehensively, how the mixing ratio of tree species in mixed forests affects the response of trees to climate and drought remains an unexplored and rather unknown question. Hence, we established tree-ring chronologies for Pinus tabuliformis Carr. (P) and Quercus variabilis Blume. (Q) mixed forests with different mixing ratios. In the temperate region of China, we investigated three mixing ratios: 90% P and 10% Q (P9Q1), 60% P and 40% Q (P6Q4), and 20% P and 80% Q (P2Q8). We collected tree ring samples using three tree size categories: dominant, intermediate, and suppressed trees. We explored the climate sensitivity of these trees and their drought tolerance indices-resilience (Rs), resistance (Rt), and recovery (Rc) under two drought conditions: short-term drought (1993 drought) and long-term drought (1999-2015 drought). P6Q4 made P. tabuliformis more sensitive to the Palmer drought severity index (PDSI) from the previous year than the other two ratios. The effect of the mixing ratio on drought response was insignificant under short-term drought in both tree species. Rt, Rc, and Rs of P. tabuliformis decreased with an increasing Q. variabilis:P. tabuliformis ratio in long-term drought. Rt, Rc, and Rs of Q. variabilis were the highest in P6Q4. The sensitivity of trees to PDSI varied among classes and was influenced by the mixing ratio. Dominant trees were most sensitive to PDSI in P6Q4 and P2Q8, whereas intermediate and suppressed trees were more sensitive to PDSI in P9Q1. The impact of tree size on drought tolerance indices varied according to drought type and mixing ratio. These findings showed that the mixing ratio has a confounding effect on the drought sensitivity of temperate tree species. Differences in hydrological niches allow Q. variabilis to benefit from mixing with P. tabuliformis. Mixing with optimal proportion of P. tabuliformis maximizes the drought resilience of Q. variabilis. Additionally, weakly competitive species (P. tabuliformis) do not benefit from mixed forests during prolonged water deficits. This result complements previous arguments that species mixing reduces the biological vulnerability of individuals. This study emphasizes the importance of species selection based on the biological and physiological characteristics of tree species in the afforestation of mixed forests. It highlights the critical role of species mixing ratios in the resistance of mixed forest ecosystems to climate change, which may provide a reference for sustainable forest management.

Slower growth prior to the 2018 drought and a high growth sensitivity to previous year summer conditions predisposed European beech to crown dieback

The record-breaking drought in 2018 caused premature leaf discoloration and shedding (early browning) in many beech (Fagus sylvatica L.) dominated forests in Central Europe. However, a high degree of variability in drought response among individual beech trees was observed. While some trees were severely impacted by the prolonged water deficits and high temperatures, others remained vital with no or only minor signs of crown vitality loss. Why some beech trees were more susceptible to drought-induced crown damage than others and whether growth recovery is possible are poorly understood. Here, we aimed to identify growth characteristics associated with the variability in drought response between individual beech trees based on a sample of 470 trees in northern Switzerland. By combining tree growth measurements and crown condition assessments, we also investigated the possible link between crown dieback and growth recovery after drought. Beech trees with early browning exhibited an overall lower growth vigor before the 2018 drought than co-occurring vital beech trees. This lower vigor is mainly indicated by lower overall growth rates, stronger growth declines in the past decades, and higher growth-climate sensitivity. Particularly, warm previous year summer conditions negatively affected current growth of the early-browning trees. These findings suggest that the affected trees had less access to critical resources and were physiologically limited in their growth predisposing them to early browning. Following the 2018 drought, observed growth recovery potential corresponded to the amount of crown dieback and the local climatic water balance. Overall, our findings emphasize that beech-dominated forests in Central Europe are under increasing pressure from severe droughts, ultimately reducing the competitive ability of this species, especially on lowland sites with shallow soils and low water holding capacity.

Feasibility of using technology to reduce adsorption reactions in single superphosphate in soybean cultivation in the Savannah

AbstractThe soils of Brazilian Savannah are generally characterized by the predominance of highly weathered and acid Oxisols, with low fertility and high aluminum content, which inhibits the availability of phosphorus (P) for plants. Thus, we seek to develop technologies that minimize P losses. In this way, the objective was to evaluate the agronomic and economic feasibility of using the technology that reduces phosphorus adsorption reactions (TRRA) associated with single superphosphate (SS) in the cultivation of soybeans (Glycine max) in the 2018–2019 and 2019–2020 harvests. The experiment was carried out in the field, in a randomized block design, with four replications and a 4 × 2 × 2 factorial scheme, where doses of 320, 400, 480, and 570 kg ha−1 of SS were used, associated or not with the use of TRRA, in the 2018–2019 and 2019–2020 harvests. The components of yield, grain yield, and economic feasibility were evaluated, calculating the operating cost and the point of maximum economic efficiency (PMEE). The PMEE in the 2018–2019 season occurred with the application of 568 kg ha−1 of SS and, in the 2019–2020 season, it was found with the application of 320 kg ha−1 of SS + TRRA. The best weather conditions in the 2019–2020 season (absence of prolonged water deficit) influenced productivity and improved TRRA efficiency. The economic analysis indicates that the use of TRRA increases the productivity of the soybean crop, generating greater net income for the producer. However, benefits may vary depending on weather conditions.

Using thermal imagery and changes in stem radius to assess water stress in two coniferous tree species

With a warming climate and greater evaporative demand, many forest ecosystems are increasingly affected by water limitation as prolonged water deficits reduce tree-level growth and survival. Water deficit can be monitored in several ways, including from daily measurements of sap flow or changes in stem radius from automated sensors mounted on individual trees. As an alternative approach, we evaluated the use of airborne thermal imagery from unmanned aerial vehicles as a rapid, scalable tool for assessing tree-level water stress. Plant water stress leads to higher leaf temperatures when soil moisture is low and evaporative demand is high. To detect this response, we modeled the difference between leaf and air temperature (∆T) as a function of local soil moisture, vapor pressure deficit, and wind speed for two tree species, lodgepole pine (Pinus contorta var. latifolia) and white spruce (Picea glauca). We used those same weather and soil conditions to model dendrometer-based measurements of daily changes in internal tree water deficit (∆TWD). While canopy leaf temperature and daily change in tree water deficit showed little direct correlation with one another, these variables both responded to soil moisture, vapor pressure deficit, and wind speed in a manner that reflects responses to water stress as soil became progressively drier over the summer months. The two species showed some differences related to species-specific strategies for drought avoidance. The application of thermal imagery to detect water stress in natural forest ecosystems can improve understanding of how trees experience water stress across species and environmental conditions.

Contrasting sensitivity of soil bacterial and fungal community composition to one year of water limitation in Scots pine mesocosms.

The soil microbiome is crucial for regulating biogeochemical processes and can thus strongly influence tree health, especially under stress conditions. However, little is known about the effect of prolonged water deficit on soil microbial communities during the development of saplings. We assessed the response of prokaryotic and fungal communities to different levels of experimental water limitation in mesocosms with Scots pine saplings. We combined analyses of physicochemical soil properties and tree growth with DNA metabarcoding of soil microbial communities throughout four seasons. Seasonal changes in soil temperature and soil water content and a decreasing soil pH strongly influenced the composition of microbial communities but not their total abundance. Contrasting levels of soil water contents gradually altered the soil microbial community structure over the four seasons. Results indicated that prokaryotic communities were less resistant to water limitation than fungal communities. Water limitation promoted the proliferation of desiccation-tolerant, oligotrophic taxa. Moreover, water limitation and an associated increase in soil C/N ratio induced a shift in the potential lifestyle of taxa from symbiotic to saprotrophic. Overall, water limitation appeared to alter soil microbial communities involved in nutrient cycling, pointing to potential consequences for forest health affected by prolonged episodes of drought.

Concurrent time course of xylem hydraulic dysfunction and non-structural carbohydrates under contrasting water deficits and nitrogen supplies in poplar

We compared the temporal dynamics of growth, leaf gas exchange, xylem hydraulic dysfunction and non-structural carbohydrates (NSC) of two poplar hybrid genotypes subjected to a differential nitrogen (N) supply under contrasting water deficits. Moderate water deficit generated intermediate embolism rates (45–70%) but had marginal effects on NSC. Severe water deficit generated progressive hydraulic failure and NSC reduction, leading to tree death within 90 days. At death, NSC in perennial tissues were not entirely depleted because of remaining soluble sugars. Higher N availability primarily affected growth and NSC dynamics (mainly starch), not embolism dynamics. The faster growing genotype benefiting most from N addition ceased growth and photosynthesis almost simultaneously, with no effect of N addition on process cessation, leading to progressive starch depletion during severe drought. In contrast, the slower growing genotype ceased growth before photosynthesis, leading to a transient increase in starch concentration during early drought stages, but this tended to be suppressed by higher N availability. Altogether, our findings indicate that carbon starvation alone is unlikely in hydraulically vulnerable species such as poplar even under prolonged moderate water deficit, but starch relative depletion covaries in time with progressive hydraulic failure under lethal water deficit. Nutritional status has the potential to shape drought responses, primarily through adjustments in carbon source-sink relations rather than in intrinsic xylem hydraulics, in a genotype-dependent manner. Exploring how hydraulic and carbon safety margins can be coordinated within species would be valuable in understanding how variation in drought response strategies can be exploited in breeding/selection.

Simulating maize water productivity at deficit irrigated field in north west Ethiopia.

Irrigation agriculture in Ethiopia can be improved by applying appropriate irrigation levels. Since water scarcity is the major problem in Ethiopia, and farmers apply water without knowledge of the amount of water to be applied, appropriate irrigation levels for maize crops should be investigated in the central Gondar zone, Ethiopia. This paper aims to investigate the effect of deficit levels of irrigation on crop parameters and evaluate the AquaCrop model for its predictability potential of water productivity. The experiment has four levels of water application (Full Irrigation (100%), 75%, 50%, and 25% of crop evapotranspiration) at 10days of irrigation interval using Randomized Complete Block Design with three replications. Data collected in two experiments in the different seasons were soil moisture, canopy cover, biomass, and final yield. As high R 2 (0.93) and Nash-Sutcliffe Efficiency (NSE) (0.91) values indicated, the model performed well in simulating canopy cover, above-ground biomass, and yield in all treatments except 25% full irrigation (FI) with prolonged water deficit. Grain yield measured from experiment 2 was within the range of 4.6 t/ha to 7.4 t/ha. Even though a high yield was found from FI, the measured water use efficiency was better in 75% FI treatment, indicating a potential for water-saving by this treatment than FI. Higher grain yield was observed for maize sown in January at experiment 1. This was attributed to the rainfall impact on the experiment since it was spring season in Ethiopia at which some rainfall in the region is pronounced. In addition, AquaCrop thoroughly underestimated the seasonal evapotranspiration values and the deviations were commonly bigger as stress levels increased. Therefore, AquaCrop can be used in the simulation of crop parameters, prediction of irrigated outputs, and assessing the impact of irrigation scheduling.

ЭМБРИОНАЛЬНЫЕ ДАННЫЕ В БИОТЕХНОЛОГИЧЕСКИХ ИССЛЕДОВАНИЯХ ЗАСУХОУСТОЙЧИВОСТИ ПШЕНИЦЫ В ЦЕЛЯХ СЕЛЕКЦИИ

Drought as an unfavorable combination of meteorological conditions under which plants experience a prolonged water shortage in the air and soil is one of the most common abiotic stress factors, the effect of which leads to significant crop losses of economically important plants, including cereals. One of the promising directions of biotechnological assessment of the resistance of existing and newly created genotypes of cereals to this abiotic stress factor for breeding purposes is the use of embryo culture in vitro, when embryos of the particular stage of development are used as explants. Especially promising is the in vitro cultivation of immature embryos that are at the critical stage of autonomy. Such embryo does not depend on the physiological factors of the maternal individual and is able to independently give rise to a full-fledged regenerant under adequate in vitro conditions. At the same time, to identify the stage of autonomy, complex cytophysiological studies of the embryo in the dynamics of development from the zygote to the mature structure are necessary. Embryonic analysis is also necessary during evaluation of the obtained regenerants in the laboratory ex vitro and especially in the field in vivo conditions. The review article, using the example of spring soft wheat, presents some results of comprehensive investigation by the researchers of the plant physiology laboratory UIB UFRC RAS on the use of cytophysiological data to identify the critical stage of embryo autonomy, as well as on the application of the obtained results in the elaboration of biotechnology of embryo culture in vitro. Together with the researchers of the laboratory of breeding and seed production of spring wheat of the RIAS UFRC RAS, the prospects of using culture in vitro of immature autonomous embryos in the creation of drought-resistant hybrid wheat lines are shown. Experimental studies were conducted on the basis of theoretical formulation by RAS corresponding member T.B. Batygina, whose memory this article is dedicated to.

Water retention and metabolic changes improve desiccation tolerance in Barbacenia graminifolia (Velloziaceae).

Barbacenia graminifolia is a Velloziaceae species endemic to the campos rupestres in Serra do Cipó, Minas Gerais state (Brazil). This biome is characterised by high irradiance and limited water conditions. Unlike other resurrection plants, B. graminifolia can maintain a high hydric status (>80%) after 28 days of water suppression before desiccation. We investigated the physiological and metabolic mechanisms associated with structural changes that allow B. graminifolia to maintain hydration under a prolonged water deficit and to recover after desiccation. After 30 days of water deficit, desiccated plants exhibited chlorophyll degradation, a 178.4% and 193.7% increase in total carotenoids and MDA, respectively, and twice the CAT and APX activity compared to hydrated plants. The metabolite profile showed increased amino acids, carbohydrates, saturated fatty acids and benzoic acids during dehydration, while trichloroacetic acid cycle acids were higher in hydrated and rehydrated plants. Anatomical and ultrastructural data corroborated the physiological and metabolic changes and revealed the presence of mucilaginous cells with high water retention capacity. Our data indicated that combined strategies of assimilatory metabolism shutdown, accumulation of compatible solutes and antioxidant compounds, increase in hydrophilic molecules, changes in the composition of membrane lipids and remodelling of cell organelles conditioned the efficiency of B. graminifolia in delaying water loss, tolerating further desiccation and quickly recovering after rehydration. These attributes evidence that this species is well adapted to cope with adverse environmental conditions, mainly directing the metabolism to an efficient antioxidant response and improving its capacity to retain water during the dry season.

Physiological and Structural Responses to Prolonged Water Deficit in Young Trees of Two Olive Cultivars.

This study aimed to characterize the physiological and structural responses of potted one-year-old olive trees belonging to two olive cultivars—‘Nocellara del Belice’ and ‘Cerasuola’—exposed to prolonged drought under greenhouse conditions. Two irrigation treatments based on evapotranspiration (ET) were imposed for 69 days, i.e., well-watered (WW, 100% ET) and drought-stressed (DS, 10–30% ET). Leaf stomatal conductance (gs), stem water potential (Ψstem), transpiration (E), photosynthetic capacity (Amax), water use efficiency (WUE), stem (Kstem) and root (Kroot) hydraulic conductance, trunk diameter variations (TDV), and leaf patch attenuated pressure fluctuations (pp, a proxy of the inverse of leaf turgor pressure) were measured in WW and DS trees at different stages of the experiment. Leaf gs did not significantly differ between cultivars under DS, whereas differences in Ψstem only became significant at the end of prolonged drought, when ‘Nocellara del Belice’ experienced Ψstem < −4 MPa. ‘Cerasuola’ trees expressed the best WUE under drought, although they were more susceptible to photoinhibition under optimal plant water status. Both cultivars tended to increase their Kstem at the end of the drought period. A marked reduction in Kroot occurred in ‘Cerasuola’ plants after prolonged drought; however, a similar mechanism was not observed in ‘Nocellara del Belice’. The ratio between Kstem and Kroot exponentially increased towards the end of the prolonged drought period in both cultivars, but more markedly in ‘Cerasuola’. TDV and pp trends suggested that ‘Cerasuola’ plants keep better plant water status under severe drought compared to ‘Nocellara del Belice’ by maintaining high leaf turgor and reduced trunk diameter fluctuations. These responses may be related to reduced cell wall elasticity and xylem vessel size and/or wall thickness—drought avoidance mechanisms. The Kstem/Kroot ratio can serve as an indicator of drought stress avoidance mechanisms to compare genotype-specific responses to drought stress.

Can prolonged conditions of water deficit alter photosynthetic performance and water relations of coffee plants in central-west Colombia?

In the coffee-growing areas of Colombia, the vulnerability of soils to conditions of water deficit has been determined and this limitation has been projected to increase its intensity and severity during extreme climatic scenarios, which constitute one of the factors limiting coffee production. The objective of this study was to evaluate the effect of prolonged water deficit conditions on the physiological performance of coffee plants cv. Castillo ®. The evaluations were carried out in 13-month-old “Castillo®” variety plants established in a greenhouse which were subjected to two conditions: well-watered at field capacity and water deficit in the soil-applied through withholding the water supply for 40 days, using a completely randomized experimental design. Leaf water potential (Ψpd and Ψmd), gas exchange, and chlorophyll fluorescence parameters (Fv/Fm and ETR) were measured. In the plants with water deficit, Ψpd and Ψmd were decreased significantly. Five days after restricting the water supply, the gs was significantly reduced to 95% at the end of the experiment compared to plants without stress. The Fv/Fm and ETR parameters showed no sensitivity under the water deficit conditions. Plants under water deficit decreased Amax by 81%, Isat by 61%, and Rd by 50%, as compared to plants without stress. The transpiration and water-use efficiency decreased, while Ci had a greater concentration in plants under water deficit. These results indicate the physiological performance coffee cv. Castillo ® plants were significantly affect by prolonged conditions of soil water deficit and that the reductions in photosynthetic processes were related to stomatal limitations.

Morphology, biochemistry, and yield of cassava as functions of growth stage and water regime

Water deficit affects morphological attributes and physiological and biochemical processes important to plants. Although cassava crop is known for its rusticity and adaptability to adverse environmental conditions, there have not been any studies reporting the effects of water deficit at different growth stages on cassava morphology and biochemistry. The objective of this research was to evaluate the morphological, anatomical, biochemical, and yield responses of cassava under different water regimes in three growth stages. The experimental design used was completely randomized 3 × 3 factorial scheme consisting of three growth stages (GS) [90–180 (GS3), 180–270 (GS4), and 270–360 days after planting (DAP) (GS5)] and three soil water tensions (-10, -40, and -70 kPa) with five replicates. Plants were affected, mainly in GS3, by -40 and -70 kPa soil tensions, with decreases in stem diameter, plant height and number of leaves. Leaf anatomy was also affected by water deficit in GS3, with reductions in the mesophyll thickness (13.7%), spongy parenchyma (19.9%), epidermal cells on the blade abaxial surface (18.0%) and in the number of xylem vessels (15.8%); in addition, there was an increase in the wall thickness (105.0%) and in the diameter (85.5%) of the xylem vessels. Under prolonged water deficit, there was an increase in the activity of superoxide dismutase and catalase, which were efficient in controlling H2O2. The imposition of water deficit drastically reduced the yield of commercial and tuberous roots in GS3 (82.1% and 65.0%) and GS5 (45.7% and 32.5%). Our study shows that the period of crop susceptibility to water deficit is longer than previously thought, evidencing the need for greater attention to water availability between 90 and 180 and between 270 and 360 DAP, as it may aid in reducing the negative effects of water deficit on the biochemistry, anatomy, and yield components of cassava.

Root traits in Crambe abyssinica Hochst and Raphanus sativus L. plants are associated with differential tolerance to water deficit and post-stress recovery

Background Previous studies have shown that Crambe abyssinica and Raphanus sativus are physiologically tolerant to water deficits; however, there is a lack of information on the mechanisms responsible for their tolerance regarding root morphological characteristics. This study aimed to characterize morphological changes in the root system of C. abyssinica and R. sativus subjected water deficit, as well as to identify the responses that improve tolerance and post-stress recovery capacity of these plants. Methods Independent experiments for each specieswere performed in a controlled greenhouse, where plants were randomly set in a randomized block design with five replicates. Plants of C. abyssinica and R. sativus were cultivated in pots and exposed to well-watered treatment (WW; 90% water holding capacity–WHC of the substrate) or water deficit (WD; 40% WHC) conditions, at 28 days after planting. The plants were kept under WD for 7, 14, or 21 days with rehydration soon after each episode of water deficit. Assessment of water relations, biomass allocation, leaf and root system morphological characteristics and gas exchange were performed after each period of water deficit and 48 h after rehydration. Results The water deficit reduced the water status of both species, and morphological and biomass allocation were not recovered after rehydration. Photosynthesis of C. abyssinica decreased with prolonged water deficit, which was also not recovered after rehydration. In R. sativus, photosynthesis was not altered by WD for 21 days, and a higher WUE was recorded. Root morphology of R. sativus was mainly affected at 14 days of WD, while the traits related to very fine roots increased at 21 days of WD, when compared to WW plants. Thus, R. sativus has shown greater tolerance to water deficits mainly due to the presence of very fine roots throughout the period of stress, when compared to C. abyssinica in which the fine roots predominated.

Leaf transcriptome profiling of contrasting sugarcane genotypes for drought tolerance under field conditions

Drought is the most detrimental abiotic stress to sugarcane production. Nevertheless, transcriptomic analyses remain scarce for field-grown plants. Here we performed comparative transcriptional profiling of two contrasting sugarcane genotypes, ‘IACSP97-7065’ (drought-sensitive) and ‘IACSP94-2094’ (drought-tolerant) grown in a drought-prone environment. Physiological parameters and expression profiles were analyzed at 42 (May) and 117 (August) days after the last rainfall. The first sampling was done under mild drought (soil water potential of −60 kPa), while the second one was under severe drought (soil water potential of −75 kPa). Microarray analysis revealed a total of 622 differentially expressed genes in both sugarcane genotypes under mild and severe drought stress, uncovering about 250 exclusive transcripts to ‘IACSP94-2094’ involved in oxidoreductase activity, transcriptional regulation, metabolism of amino acids, and translation. Interestingly, the enhanced antioxidant system of ‘IACSP94-2094’ may protect photosystem II from oxidative damage, which partially ensures stable photochemical activity even after 117 days of water shortage. Moreover, the tolerant genotype shows a more extensive set of responsive transcription factors, promoting the fine-tuning of drought-related molecular pathways. These results help elucidate the intrinsic molecular mechanisms of a drought-tolerant sugarcane genotype to cope with ever-changing environments, including prolonged water deficit, and may be useful for plant breeding programs.

Osmolyte-induced water deficit stress mitigation during panicle initiation stage in transplanted rice (Oryza sativa L.)

A field experiment was conducted to observe the osmolyte-induced water deficit stress mitigation during the panicle initiation stage in transplanted rice (Oryza sativa L. cv. BRRI dhan72). At the panicle initiation stage, plants were simulated with four levels of water regimes viz., well-irrigated (D0), water deficit for 5 d (D1), 10 d (D2) and 15 d (D3). Plants were treated with or without 10 mM of proline (Pro) and trehalose (Tre) as foliar spray started at mid-vegetative stage and continued till the end of stress period. Results revealed that water deficit stress drastically reduced most of the plant morpho-physiological attributes while other yield contributing characters were also affected due to prolonged water deficit stress. However, exogenous application of osmolytes like Pro and Tre significantly increased all those morphological, physiological and yield contributing parameters. Foliar addition of osmolytes concomitantly decreased the number of non-effective tillers hill-1 and the number of unfilled grain panicle-1 under water stress condition. Although both the osmolytes performed well under multiple duration of drought stress, the application of 10 mM Pro markedly improved all growth and yield contributing parameters under D1 water deficit stress compared to other stress durations. Hence, it may be concluded that the use of osmolytes would be a prospective remedy against moderate water deficit stress in transplanted rice production.

High growth recovery ability of Eucalyptus grandis trees following a 3-year period of 80% throughfall reduction

Eucalyptus plantations are already planted in - or expanding to - water-limited regions with a high risk of severe drought. In future drier and more variable climate including extreme events, the ability of trees to recover after severe droughts emerges as a crucial for the sustainability of forest plantations.An original experiment involving 80% reduction in throughfall was set up in Brazil to gain insight into the responses of Eucalyptus grandis trees to prolonged (3-year) extreme water deficit and the ability of this species to recover following water stress. Our study focused on the changes in basal area, stem radius, and total height measured by high-temporal resolution dendrometers and periodical surveys of trees affected by 80% throughfall reduction (treatment group) and in a control group. The differences in basal area, stem radius, and total height growth rate were compared between groups over (i) 37 months of 80% throughfall reduction and (ii) 31 months following the end of 80% throughfall reduction. The correlations among growth rates, stem radius fluctuations, and meteorological variables in each group were determined to gain insights into the trees’ responses to environmental conditions and stem water status.The 80% reduction in throughfall over 3 years significantly reduced tree growth rates by 73% in basal area and 95% in total height. However, under normal water availability following throughfall reduction, the basal area growth rate of water-stressed trees was 97% higher than that of the control trees while total height growth rate was only 8% higher. Despite the severe water stress, no tree mortality was observed. Trees recovered 51% of their basal area over the 31-month recovery period. In contrast, only 5% of total height was recovered.In the treatment group, rapid responses to variation in rainfall events were observed during the 80% throughfall reduction period. Also, correlations between stem radius fluctuations and vapor pressure deficit indicate increased transpiration following the end of throughfall reduction. These relationships indicate high conservation of the integrity of the xylem vascular system over the 3 years of 80% throughfall reduction, a key factor in the increased resilience of the trees. In the absence of tree mortality, our results suggest the 80% throughfall reduction had a severe impact on tree growth but demonstrate great recovery ability of Eucalyptus grandis trees in basal area growth following such a severe water deficit.