Mild Drought Stress Research Articles

Effects of drought stress on physiological and biochemical and chemical components of Cinnamomum cassia seedlings

Six month old Cinnamomum cassia seedlings were used to simulate drought stress with polyethylene glycol(PEG 6000). The physiological indicators(osmotic substances, antioxidant enzymes, etc.) and chemical components of seedlings under different drought levels and the correlation between the two were studied. The results showed that the chlorophyll content and relative water content decreased gradually with the increase of PGE 6000(0, 5%, 10%, 15%) concentration and time(3, 5, 7 d), while the soluble protein content, soluble sugar content and catalase(CAT) activity increased, but the rising rate slowed down with the time. The activities of peroxidase(POD), superoxide dismutase(SOD), malondialdehyde(MDA) and proline content increased at first and then decreased. The content of coumarin, cinnamaldehyde, cinnamic acid and dimethoxycinnamaldehyde decreased, while the content of cinnamyl alcohol continued to increase.Under drought stress, the fluorescence signals of reactive oxygen species and no contents in roots of C. cassia seedlings were significantly stronger than those of the control.Further correlation analysis showed that coumarin content, di-methoxycinnamaldehyde content and osmoregulation substance content were significantly negatively correlated(P<0.05), cinnamic acid content was significantly negatively correlated with POD and SOD activities(P<0.01).It was found that C. cassia seedlings showed a certain degree of drought tolerance under short-term or mild drought stress, but if the drought exceeded a certain degree, the physiological metabolism of the seedlings would be unbalanced.

Irrigation and fertilizer treatments affecting rosmarinic acid accumulation, total phenolic content, antioxidant potential and correlation between them in peppermint (Mentha piperita L.)

One of the greatest challenges in recent years is providing enough food to feed the increasing world population, while available freshwater resources become limited. However, effective fertilizer management has also a fundamental role to improve yield quality and quantity. A field experiment was conducted over 2 years, using a split-plot arrangement in a randomized complete block design. The experiments had three water deficit severity treatments: 25% (control), 40% (mild stress), and 55% (severe stress) depletion from the available water. The subplot division consisted of six fertilizer treatments; FR1: unfertilized (control), FR2: 140 kg ha−1 urea; FR3: 105 kg ha−1 urea + 3.3 ton ha−1 vermicompost; FR4: 70 kg ha−1 urea + 6.6 ton ha−1 vermicompost; FR5: 35 kg ha−1 urea + 10 ton ha−1 vermicompost, and FR6: 13.5 ton ha−1 vermicompost. The maximum essential oil (0.97%) was observed under mild water deficit stress. The highest antioxidant activity (DPPH) and superoxide dismutase activity could be monitored under unfertilized and 140 kg ha−1 urea fertilized conditions, respectively. Vermicompost-treated soils reduced antioxidant features, total phenol, and rosmarinic acid content under water deficit. These results indicate that mild drought stress can increases the synthesis of medical compound and vermicomposting can alleviate the impact of drought by conserving soil moisture and improve nutrient uptake. Therefore, the results suggest that using vermicompost as a fast-acting nitrogen amendment can improve the leaf area index.

The transcriptomic landscapes of rice cultivars with diverse root system architectures grown in upland field conditions.

Root system architecture affects plant drought resistance and other key agronomic traits such as lodging. However, although phenotypic and genomic variation has been extensively analyzed, few field studies have integrated phenotypic and transcriptomic information, particularly for below-ground traits such as root system architecture. Here, we report the phenotypic and transcriptomic landscape of 61 rice (Oryza sativa) accessions with highly diverse below-ground traits grown in an upland field. We found that four principal components explained the phenotypic variation and that accessions could be classified into four subpopulations (indica, aus, japonica and admixed) based on their tiller numbers and crown root diameters. Transcriptome analysis revealed that differentially expressed genes associated with specific subpopulations were enriched with stress response-related genes, suggesting that subpopulations have distinct stress response mechanisms. Root growth was negatively correlated with auxin-inducible genes, suggesting an association between auxin signaling and upland field conditions. A negative correlation between crown root diameter and stress response-related genes suggested that thicker crown root diameter is associated with resistance to mild drought stress. Finally, co-expression network analysis implemented with DNA affinity purification followed by sequencing analysis identified phytohormone signaling networks and key transcription factors negatively regulating crown root diameter. Our datasets provide a useful resource for understanding the genomic and transcriptomic basis of phenotypic variation under upland field conditions.

Soil Water Deficit and Fertilizer Placement Effects on Root Biomass Distribution, Soil Water Extraction, Water Use, Yield, and Yield Components of Soybean [Glycine max (L.) Merr.] Grown in 1-m Rooting Columns.

Typical small-pot culture systems are not ideal for controlled environment phenotyping for drought tolerance, especially for root-related traits. We grew soybean plants in a greenhouse in 1-m rooting columns filled with amended field soil to test the effects of drought stress on water use, root growth, shoot growth, and yield components. There were three watering treatments, beginning at first flower: watered daily to 100% of the maximum soil water holding capacity (control), 75% (mild drought stress), or 50% (drought stress). We also tested whether applying fertilizer throughout the 1-m soil depth instead of only in the top 30 cm would modify root distribution by depth in the soil profile and thereby affect responses to drought stress. Distributing the fertilizer over the entire 1-m soil depth altered the root biomass distribution and volumetric soil water content profile at first flower, but these effects did not persist to maturity and thus did not enhance drought tolerance. Compared to the control (100%) watering treatment, the 50% watering treatment significantly reduced seed yield by 40%, pod number by 42%, seeds per pod by 3%, shoot dry matter by 48%, root dry matter by 53%, and water use by 52%. Effects of the 75% watering treatment were intermittent between the 50 and 100%. The 50% treatment significantly increased root-to-shoot dry matter ratio by 23%, harvest index by 17%, and water-use efficiency by 7%. Seed size was not affected by either fertilizer or watering treatments. More than 65% of the total root dry matter was distributed in the upper 20 cm of the profile in all watering treatments. However, the two drought stress treatments, especially the mild drought stress, had a greater proportion of root dry matter located in the deeper soil layers. The overall coefficient of variation for seed yield was low at 5.3%, suggesting good repeatability of the treatments. Drought stress imposed in this culture system affected yield components similarly to what is observed in the field, with pod number being the component most strongly affected. This system should be useful for identifying variation among soybean lines for a wide variety of traits related to drought tolerance.

Relationships between diurnal and seasonal variation of photosynthetic characteristics of Eucalyptus plantation and environmental factors under dry-season irrigation with fertilization

Eucalyptus is widely planted in South China and has high economic and ecological values. However, the seasonal drought in southern China severely limits the productivity of Eucalyptus plantation. In this study, the dry-season irrigation was carried out after the conventional production and planting of Eucalyptus. The diurnal changes of photosynthetic characteristics of Eucalyptus plantations were measured in July, October 2017 and January, May 2018 to explore the diurnal and seasonal variations and their responses to both dry-season irrigation and environmental factors. The results showed that during the first-year growth of Eucalyptus urophylla × E. grandis plantation, (1) the diurnal changes of the trees under different treatments showed single-peak curves with the varied occurrence time of the highest photosynthetic characteristics in different months; the E. urophylla × E. grandis without dry-season irrigation (CK and F) had transpiration midday depression in January and that with the only dry-season irrigation (W) exhibited both photosynthetic and transpiration midday depression in May. (2) The trees of CK and F were subjected to mild drought stress in the dry season and their maximum photosynthetic and transpiration rate were lower than those of W and WF treatment respectively, but they had higher maximum WUE. The trees of W had significantly higher daily net CO2 assimilation and daily water transpiration in dry season. (3) The diurnal changes of photosynthetic characteristics were mainly influenced by water vapor pressure deficit (VPD) at the corresponding time of the month. (4) In the short-term treatments, dry-season irrigation and fertilization significantly increased the biomass of E. urophylla × E. grandis. Dry-season irrigation alleviated the mild drought stress for gas exchange in the dry season and further promote the biomass of E. urophylla × E. grandis. This study provided an important practical exploration for improving the productivity of E. urophylla × E. grandis plantation in seasonal arid areas.

Cross priming with drought improves heat-tolerance in chickpea (Cicer arietinum L.) by stimulating small heat shock proteins and antioxidative defense

An expected rise in global temperature is an inevitable threat to crop productivity and may have serious concerns on food security. In northern India, winter-sown chickpea (Cicer arietinum L.) come across with abrupt high temperature during the terminal reproductive stage which leads to reduction in the production. Priming chickpea with mild drought at the seedling stage may induce tolerance to heat stress at a later stage. We analyzed 11 days old seedlings of two contrasting chickpea varieties (PBG1 and PBG5) primed with mild drought stress for 3 days, recovered for another 6 days, and finally exposed to different levels of heat stress (30 °C, 32 °C, 34 °C, and 36 °C) for 12 h. Both damage and defense parameters were analyzed at different stages i.e. before and after priming and finally after exposure to varying degrees of stress. Our study revealed that priming improved membrane integrity by reducing percent electrolyte leakage and lipid peroxidation up to 34 °C, whereas mitochondrial efficiency (2,3,5-triphenyl tetrazolium chloride (TTC) reduction) could not be influenced. Superoxide dismutase, catalase and ascorbate peroxidase activity increased proportionately with the increase in temperature (up to 34 °C only). Later, activity declined at higher temperatures. Changes in the expression level of Small Heat Shock Proteins (sHSP18.5 and 22.7) were also established by RT-PCR. Primed plants showed increased expression of sHSP at 36 °C. Overall, priming with drought reduced the membrane damage and increased antioxidative enzymes, also modulated expression of sHSP18.5 and 22.7; thus, improved the heat tolerance up to 34 °C. This study has highlighted the role of drought priming in the acclimation to heat stress and corroboration of antioxidative enzymes and sHSP’s.

Rhizospheric Bicarbonate Improves Glucose Metabolism and Stress Tolerance of Broussonetia papyrifera L. Seedlings under Simulated Drought Stress

Heavy concentrations of bicarbonates present throughout karst ecosystems necessitate identification of the role of $${\text{HCO}}_{3}^{ - }$$ in plant growth, especially when under drought stress. We aim to elucidate effect of different concentrations of $${\text{HCO}}_{3}^{ - }$$ on paper mulberry (Broussonetia papyrifera L.) seedlings growth under drought stress. Effects of four bicarbonate concentrations (0, 3, 6, and 9 mM) with simulated mild drought stress on growth, glucose metabolism, photosynthetic traits, self-protective abilities and extent of cell damage were examined. Compared with other treatments, plants under 3 mM bicarbonate with simulated mild drought stress showed the best osmotic adjustment and reactive oxygen species scavenging ability, the highest total activity of glucose catabolism enzymes and glucose-6-phosphate dehydrogenate activity, and the highest growth rate. Specific concentration of $${\text{HCO}}_{3}^{ - }$$ reduce negative influence in Broussonetia papyrifera L. under drought stress. Due to both producing more metabolic substrate and activating pentose phosphate pathway, those plants showed stronger resistance, therefore might suffer less harm and retain a better growth status under mild drought stress. This suggests that when specific plants in a karst environment are suffering drought stress, specific concentration of $${\text{HCO}}_{3}^{ - }$$ benefit to their growth.

Effects of drought and rehydration on the growth and physiological characteristics of mustard seedlings

The mustard variety Felicia was used to analyze the response and compensation effects of growth and physiology under drought stress and rehydration conditions at the seedling stage. The seedlings were exposed to different levels of drought stress simulated by polyethylene glycol (PEG). The growth parameters, fresh weight, chlorophyll fluorescence, and antioxidant system were measured. The results showed that drought stress inhibited the growth of roots and shoots and reduced the performance of photosystem II (PS II). After rehydration, the root length and fresh weight of plants rapidly increased, and the performance index (PIABS) was found to be higher compared with the control, which suggested a compensative effect. The chlorophyll content was significantly reduced under moderate and severe drought stress. However, it increased under mild stress conditions. After rehydration, the chlorophyll content under moderate and severe stress did not return to the levels of control, and there was no significant difference between mild stress and the control. Under drought stress, the activities of antioxidant enzymes and content of malondialdehyde (MDA) increased significantly in the leaves. After rehydration, MDA and the activities of antioxidant enzyme were higher than those of the control group, particularly under moderate and severe stress. Therefore, these results suggest that mustard is strongly adapted to mild drought stress through the efficient activities of antioxidant enzymes activity and photosynthesis, as well as its rapid recovery after rehydration.

Phenotypic Plasticity of Drought Tolerance Traits in a Widespread Eucalypt (Eucalyptus obliqua)

Long-term studies of tree responses to drought stress help us to understand the capacity of species to adapt to their environment. In this study, we investigated how Eucalyptus obliqua adjusts physiological and morphological traits in response to seasonal and multi-year droughts. We monitored physiological and morphological traits over multiple years in undisturbed control and throughfall reduction plots in a eucalypt forest in south-eastern Australia. The throughfall reduction treatment did not induce significantly lower soil moisture in the throughfall reduction plots compared with the control plots. However, natural variability in precipitation and evaporative demand induced drought stress of varying intensity each summer in all plots. We observed a significant relationship between seasonal precipitation and leaf pre-dawn water potential (ΨPD), with less precipitation over summer, resulting in a decline in ΨPD and drought stress when ΨPD fell below −0.75 MPa. Eucalyptus obliqua responded to short-term summer drought through rapid leaf osmotic adjustment which lowered the leaf water potential at the turgor loss point beyond the minimum leaf water potential. Morphological adjustments, such as the reduction of leaf area to sapwood area (higher Huber Value) were moderate during the measurement period and only occurred under severe drought stress (pre-dawn water potential < −1.2 MPa). Overall, E. obliqua responded to short-term mild drought stress through physiological trait plasticity, while morphological adjustment only occurred under a more severe water deficit.

Influence of arbuscular mycorrhiza fungi and drought stress on fatty acids profile of sesame (Sesamum indicum L.)

Abstract Drought stress is one of the most important environmental stresses which influences plant growth and development; and limits plant production. Mycorrhiza-inoculated plants often have greater tolerance to drought stress than non-mycorrhizal plants. In the present study, the effect of drought stress together with arbuscular mycorrhiza fungi (AMF) was investigated on agro-physio-chemical characteristics and oil compositions of sesame. Irrigation level (normal irrigation, mild drought stress, and severe drought stress), and mycorrhizal inoculation (Funneliformis mosseae, Rhizophagus intraradices, and non-inoculated plants) were included as treatments. Combined analysis of variance over 2 years of data revealed that the impact of irrigation and AMF was significant on mycorrhizal root colonization, non-enzymatic antioxidants, leaf phosphorus content, free amino acids and total soluble protein contents, oil yield and compositions, and plant seed yield. Mean comparisons indicated that with increasing severity of drought stress, mycorrhizal root colonization, seed yield, total chlorophyll, total soluble protein, oil yield and percentage, leaf phosphorus, total flavonoid and unsaturated fatty acids diminished. However, the amount of free amino acids, phenol, anthocyanin, carotenoids, saturated fatty acids and the ratio of saturated to unsaturated fatty acids rose significantly. Severe drought stress diminished the seed yield and unsaturated fatty acids levels by about 65 and 10 %, respectively, but it augmented free amino acids by about 65 %. Both AMF species inoculation treatments increased mycorrhizal root colonization, seed yield, oil yield and percentage, total soluble protein, leaf phosphorus, total chlorophyll, unsaturated fatty acids and all non-enzymatic antioxidants; however, they reduced saturated fatty acids and the ratio of saturated to unsaturated fatty acids significantly. Thus, for improving quantitative and qualitative traits of sesame, regardless of the drought stress level, AMF inoculation is recommendable.

Haplotype-Based, Genome-Wide Association Study Reveals Stable Genomic Regions for Grain Yield in CIMMYT Spring Bread Wheat.

We untangled key regions of the genetic architecture of grain yield (GY) in CIMMYT spring bread wheat by conducting a haplotype-based, genome-wide association study (GWAS), together with an investigation of epistatic interactions using seven large sets of elite yield trials (EYTs) consisting of a total of 6,461 advanced breeding lines. These lines were phenotyped under irrigated and stress environments in seven growing seasons (2011–2018) and genotyped with genotyping-by-sequencing markers. Genome-wide 519 haplotype blocks were constructed, using a linkage disequilibrium-based approach covering 14,036 Mb in the wheat genome. Haplotype-based GWAS identified 7, 4, 10, and 15 stable (significant in three or more EYTs) associations in irrigated (I), mild drought (MD), severe drought (SD), and heat stress (HS) testing environments, respectively. Considering all EYTs and the four testing environments together, 30 stable associations were deciphered with seven hotspots identified on chromosomes 1A, 1B, 2B, 4A, 5B, 6B, and 7B, where multiple haplotype blocks were associated with GY. Epistatic interactions contributed significantly to the genetic architecture of GY, explaining variation of 3.5–21.1%, 3.7–14.7%, 3.5–20.6%, and 4.4– 23.1% in I, MD, SD, and HS environments, respectively. Our results revealed the intricate genetic architecture of GY, controlled by both main and epistatic effects. The importance of these results for practical applications in the CIMMYT breeding program is discussed.

Physiological Characteristic Changes and Full-Length Transcriptome of Rose (Rosa chinensis) Roots and Leaves in Response to Drought Stress.

Rose (Rosa chinensis) is the most important ornamental crops worldwide. However, the physiological and molecular mechanism of rose under drought stress remains elusive. In this study, we analyzed the changes of photosynthetic and phytohormone levels in the leaves and roots of rose seedlings grown under control (no drought), mild drought (MD) and severe drought stress. The total chlorophyll content and water use efficiency were significantly enhanced under MD in rose leaves. In addition, the concentration of ABA was higher in the leaves compared to the roots, whereas the roots accumulated more IAA, methylindole-3-acetic acid and indole-3-propionic acid. We also constructed the first full-length transcriptome for rose, and identified 96,201,862 full-length reads of average length 1,149 bp that included 65,789 novel transcripts. A total of 3,657 and 4,341 differentially expressed genes (DEGs) were identified in rose leaves and roots respectively. KEGG pathway analysis showed enrichment of plant hormone, signal transduction and photosynthesis are among the DEGs. 42,544 alternatively spliced isoforms were also identified, and alternative 3' splice site was the major alternative splicing (AS) event among the DEGs. Variations in the AS patterns of three genes between leaves and roots indicated the possibility of tissue-specific posttranscriptional regulation in response to drought stress. Furthermore, 2,410 novel long non-coding RNAs were detected that may participate in regulating the drought-induced DEGs. Our findings identified previously unknown splice sites and new genes in the rose transcriptome, and elucidated the drought stress-responsive genes as well as their intricate regulatory networks.

Impact of water availability on root growth of sugar beet varieties

AbstractOn average, sugar beet yield in the UK is reduced by 10% due to water limitation. The root system of a plant is responsible for water uptake and hence an extensive root system is crucial to mitigate drought stress. There might be varietal differences when it comes to plant root system architecture but so far none have been reported in sugar beet. This study shows the results of 2 years of field experiments, examining the rooting patterns and overall plant growth of sugar beet under both rainfed and irrigated conditions. In the first year, three varieties were assessed, and in the second year, five varieties. No significant yield differences were found between the rainfed and irrigated treatments, which is likely due to the applied drought stress only being mild in both years. There were, however, significant varietal differences in plant growth and rooting patterns in rainfed plants which were most distinct when plants were subjected to mild drought stress. Varietal differences observed might indicate the possibility of breeding for certain root traits to mitigate drought stress in sugar beet in the future.

Seasonal variations in leaf and branch trace elements and the influence of a 3-yr 100% rainfall exclusion on Pinus massoniana Lamb.

BackgroundTrace elements are essential for the growth and survival of plants, and their concentrations and distributions in plants are effective reflections of ecological adaptation strategies. However, this aspect has seldom been addressed.MethodChanges in the leaf and branch trace elements of Pinus massoniana Lamb, induced by seasonal dynamics and in response to a 3-yr 100% rainfall exclusion, were evaluated.ResultsThe results showed that the concentrations of Fe, Cu, Zn, Cd, Ni and Cr in leaves of P. massoniana in the control group had high seasonal resolution. There were three groups according to their patterns over the growing season: (1) nutrient elements (Cu, Zn, Ni and Cd), which continuously decreased in concentration during the growing season, with the highest concentration in spring and the lowest in autumn; (2) accumulating element (Cr), which increased in concentration from spring to autumn; and (3) indifferent element (Fe), which increased in concentration from spring to summer and decreased in concentration from summer to autumn. The concentrations of trace elements in leaves and branches showed no significant differences with mild drought stress, except for Fe and Cr in leaves and Cr in branches, which significantly increased (p < 0.05) under the result of self-selection under mild drought stress. Therefore, the resultant seasonal and drought effects on trace element cycling in P. massoniana could provide theoretical support to respond to future climate change.

Evaluation of morpho-physiological traits under drought stress conditions in barley (Hordeum vulgare L.)

Drought stress is one of the major constraints limiting the production and productivity of barley. We tried to identify some indicators related to plant productivity by analyzing some agro-morphological and physiological traits in recombinant inbred lines (RILs). Plants were exposed to three water treatments: well-watered at 70% available water content (AWC), mild drought stress at 35% AWC, and severe drought stress at 10% AWC. Our results revealed that drought significantly affected most of the studied morpho-physiological traits resulting in strong decreases in yield and the studied traits. We did not observe a significant difference in water-use efficiency between severe and mild drought conditions. Therefore, the mild stress treatment was considered as the most suitable water level in our study. Genotypes with the most tillers and spikes, the highest 1,000-grain mass, and biological yields achieved higher grain yields under all water stress conditions. Therefore, these traits could be considered as useful tools in breeding programs.

Implications of intra-seasonal climate variations on chlorophyll a fluorescence and biomass in winter barley breeding program

This study aimed to explore how ten selected winter barley genotypes responded to variations in environmental conditions during the growth season by using fast chlorophyll a fluorescence and normalized difference vegetation index (NDVI) at the booting, anthesis and early grain-filling stage. Lower amount of rainfall during the anthesis induced instability in the function of PSII, observed as the positive K-band in six and the positive L-band in seven genotypes. At grain filling, all genotypes displayed negative K- and L-bands, suggesting an increase of stability within PSII. The performance index increased from booting to grain filling in most genotypes. Chlorophyll a fluorescence parameters were incorporated into the partial least squares model as explanatory variables of NDVI. After a cross-validation, the model with four latent variables was chosen explaining 75.8% variance (r = 0.870) for NDVI. The principal component analyses showed two distinct types of the reaction of the barley genotypes to the mild drought stress at anthesis.

Growth, Physiological and Biochemical Traits of Sage under the Exogenous Stimulating and Stress Factors

Sage (Salvia officinalis L.) belonging to the Lamiaceae family, as the main herb in the world is cultivated in many countries for extraction of essential oil from the leaves. One of the most important uses of the plant is to use its leaves as raw material in pharmaceutical and cosmetics industries. Interaction effects of exogenous jasmonic acid (JA) at different concentrations (0.00, 400, and 600 µM) and the applied of arbuscular mycorrhizal fungi (AMF) in soil under different moisture conditions (control or non-stress, slightdrought, and mild drought stress) on growth, and morphophysiological characteristics of sage and the quantity and quality yield of essential oil from the sage leaves were investigated. The constituents in the essential oils from the sage leaves were analyzed by GC-FID and GC/MS. Results indicated that the inoculation with AMF meaningfully increased the growth parameters sage, while, the foliar spray of JA improved only physiological traits such as soluble sugar, proline, and anthocyanin in the leaves. Experimental treatments individually increased the concentrations of 1,8-cineole in the essential oils. The interaction effects including AMF × JA, AMF × irrigation, and JA × irrigation significantly affected the essential oil yield and the morphological characteristic of sage. The highest value of the essential oil yield was obtained from AMF-inoculation × mild drought × JA at 400 µM. Finally, the exogenous application of JA along inoculation with AMF changed some characteristics of the sage plant under drought stress condition. Indeed, AMF-inoculation and the foliar spraying of JA had synergistic effects on the amounts secondary metabolites of sage especially, 1,8-cineole. In conclusion, we found that the exogenous JA along the inoculation of arbuscular mycorrhizal improves growth characteristics and quality of the essential oil of sage and enhances water deficit tolerance.

The decoupling between gas exchange and water potential ofCinnamomum camphoraseedlings during drought recovery and its relation to ABA accumulation in leaves

AbstractAimsDrought stress and the degree of drought severity are predicted to rise under highly variable patterns of precipitation due to climate change, while the capacity of trees to cope with drought recovery through physiological and biochemical adjustment remains unclear. We aimed to examine the coupling of physiology and biochemistry in trees during drought and the following recovery.MethodsPotted seedlings of Cinnamomum camphora were grown under well watered conditions prior to the experimental drought stress, which was initiated by withholding water. Seedlings were rewatered following attainment of two drought severities: mild drought (stomatal closure) and moderate drought (ψxylem = −1.5 MPa). We measured leaf-level water potential, gas exchange (photosynthesis and stomatal conductance), abscisic acid (ABA), proline and non-structural carbohydrates (NSCs) concentrations in seedlings of C. camphora during drought and a 4-day recovery.Important FindingsWe found that drought severity largely determined physiological and biochemical responses and affected the rate of recovery. Stomatal closure occurred at the mild drought stress, accompanied with ABA accumulation in leaves and decline in water potential, while leaf proline accumulation and variable NSC were evident at the moderate drought stress. More severe drought stress led to delayed recovery of gas exchange, but it did not have significant effect on water potential recovery. The relationships of water potential and gas exchange differed during drought stress and post-drought recovery. There was tight coupling between water potential and gas exchange during drought, but not during rewatering due to high ABA accumulation in leaves, thereby delaying recovery of stomatal conductance. Our results demonstrate that ABA could be an important factor in delaying the recovery of stomatal conductance following rewatering and after water potential recovery of C. camphora. Furthermore, greater drought severity had significant impacts on the rate of recovery of tree physiology and biochemistry.

Mild drought stress has potential to improve lettuce yield and quality

Lettuce (Lactuca sativa L.) is the most widespread leafy vegetable in the world, grown in several countries. However, commercially available cultivars have a low content of functional compounds, compared to several other vegetables. In addition, the postharvest period is characterized as a stressful stage, affecting the quality of this vegetable. One strategy that has been shown to be effective in increasing the content of functional compounds in plants is the application of abiotic elicitors, such as drought stress at moderate levels. In addition, there is evidence that plants submitted to these elicitors have greater tolerance to subsequent stresses, such as those arising from the postharvest storage. This study evaluated the effect of the pre-harvest application of moderate levels of drought stress on the pre and postharvest quality of lettuce. For this, lettuce plants were grown with the volume of water needed to saturate 100 % of the soil (C, control), 90 % of the soil (DS 90 %), 80 % of the soil (DS 80 %), or they were subjected to a short-term acute stress by water restriction (WR) for 4 days before harvest. After harvesting, half of plants were stored at 6−8 °C and 80 % humidity for postharvest analysis. The application of moderate drought stress resulted in plants with higher biomass in treatments DS 90 % and WR and did not affect the color or firmness of the plants. The DS 80 % treatment stood out in terms of quality parameters, as it resulted in plants with a higher content of carotenoids, chlorophylls, caffeic acid, monocaffeoyl tartaric acid, malercyl quercetin glucoside, quercetin-3-O-glucuronide, and greater total antioxidant activity at harvest. Plants submitted to moderate drought stress did not show changes in firmness during storage; but showed an increase in the content of flavonoids in WR, and in some phenolic compounds that have been negatively affected by storage. The results indicate that the application of moderate drought stress, especially at the 80 % level, represents an interesting strategy to improve the quality of this vegetable at harvest and after storage.

Effect of organic substances on wheat (Triticum spp.) productivity and soil enzyme functional stability under drought stress conditions

Application of organic inputs for arable soil is a common way to improve crop production. However, the interactions between organic amendments and drought are not fully known. The present study was conducted at Skolkovo University of Science and Technology, Moscow to compare the effect of three different organic-based supplements viz., humic acid, biochar and fulvic acid on the soil enzyme functional stability and shortterm wheat growth effects. Soil samples under same amount of organic carbon content were studied on wheat in greenhouse condition under three levels of water deficit irrigation: (1) control - no water deficit irrigation (70% of soil water holding capacity, WHC); (2) mild drought stress 50% WHC; (3) high drought stress (30% WHC). The response of the enzyme activities related to the C, N, and P cycles were analyzed after 1, 7, 14 and 28 days of incubation. The stress response of enzyme activities under drought conditions was noted to be constant and organic amendments removed it even in high drought stress. For wheat plants, stress due to limited water availability was successfully eliminated by organic amendments to an extent of mild drought levels.