Drought Resistance Capacity Research Articles

Small reservoirs can enhance the terrestrial carbon sink of controlled basins in karst areas worldwide

The concentration of Greenhouse Gas (GHG) in the atmosphere has sharply increased since the Industrial Revolution, leading to climate warming and severe environmental problems. It has become a consensus that GHG emissions of large reservoirs essentially constitute inland aquatic GHG emissions. However, questions remain regarding whether small karst reservoir (SKR) is only a substantial source of GHG emissions like large reservoirs, and how much GHG emission it can offset by affecting the terrestrial carbon sink (TCS) of its controlled basin. We selected two basins in the karst area of southwestern China, with built and planned SKRs, and quantitatively analysed the impact of the SKR on basin-scale water and carbon cycles during 2000–2020 using multi-source remote sensing data and the Google Earth Engine. Results showed that the associated increase in the TCS in the SKR-controlled basin can completely offset the GHG emissions and TCS losses caused by submerged land, resulting in a 21.48 % faster increase rate of TCS and a 12.20 % greater increase in TCS caused by human activities than in non-karst reservoir basin. Meanwhile, by intercepting both surface and groundwater runoff, the SKR-controlled basin showed a 329.55 % faster increase rate of available surface water resources than the non-karst reservoir basin, alleviating the problem of engineering water shortages and enhancing the drought resistance capacity. Moreover, in the three major karst areas worldwide, and especially in southwestern China, faster vegetation restoration and TCS increase exist in most SKR-controlled basins, and this increase is enhanced with increasing proximity to the water surface. This study revealed that SKR is more than a substantial source of GHG emissions; it can also effectively enhance the TCS and available surface water resources in controlled basin, which is of great significance for achieving carbon neutrality goals while maintaining the sustainability of water and carbon cycle in karst areas.

Exogenous Streptomyces spp. enhance the drought resistance of naked oat (Avena nuda) seedlings by augmenting both the osmoregulation mechanisms and antioxidant capacities.

Drought is a major obstacle to the development of naked oat industry. This work investigated mechanisms by which exogenous Streptomyces albidoflavus T4 and Streptomyces rochei D74 improved drought tolerance in naked oat (Avena nuda ) seedlings. Results showed that in the seed germination experiment, germination rate, radicle and hypocotyl length of naked oat seeds treated with the fermentation filtrate of T4 or D74 under PEG induced drought stress increased significantly. In the hydroponic experiment, the shoot and root dry weights of oat seedlings increased significantly when treated with the T4 or D74 fermentation filtrate under the 15% PEG induced drought stress (S15). Simultaneously, the T4 treatment also significantly increased the surface area, volume, the number of tips and the root activity of oat seedlings. Both T4 and D74 treatments elicited significant increases in proline and soluble sugar contents, as well as the catalase and peroxidase activities in oat seedlings. The results of comprehensive drought resistance capacity (CDRC) calculation of oat plants showed that the drought resistance of oat seedlings under the T4 treatment was better than that under the D74 treatment, and the effect was better under higher drought stress (S15). Findings of this study may provide a novel and effective approach for enhancing plant defenses against drought stress.

Distribution Characteristics of Drought Resistance and Disaster Reduction Capability and the Identification of Key Factors—A Case Study of a Typical Area in the Yun–Gui Plateau, China

Karst areas are characterized by poor surface water storage capacity, which makes them more sensitive to drought events. To enhance drought resistance in karst landform areas, this study focuses on a typical region in the Yun–Gui Plateau of China, specifically Guizhou Province, which includes 88 counties and districts. According to the regional characteristics, the index system for the assessment of drought resistance and disaster reduction ability was constructed to include 17 indexes in five evaluation layers, including natural conditions, water conservancy project, economic strength, water usage and water conservation level, and emergency support capacity. A comprehensive evaluation was conducted using a fuzzy evaluation model. Furthermore, the drought resistance and disaster reduction capacity of Guizhou Province was evaluated according to the fulfillment of water supply and water demand under the frequency of 75%, 90%, 95%, 97%, and 99% drought frequency inflow in each research unit. This assessment serves to define the spatial distribution pattern of drought resistance and disaster reduction capability within the province. Additionally, according to the results of the supply–demand balance method, the weight of the main influencing factors in regards to drought resistance and disaster reduction ability was optimized and adjusted to identify the key restricting factors of drought resistance and disaster reduction ability. This research data was obtained from the National Disaster Survey database, aiming to provide practical guidance for drought resistance in Guizhou Province. The research findings show that: (1) the distribution characteristics of drought resistance and disaster reduction capability in Guizhou Province are the most significant in Guiyang City, Liupanshui City, and Anshun City in the southwest, with higher drought resistance and disaster reduction ability found in central region, and lower drought resistance primarily identified in the eastern part of Qiandongnan Prefecture, Tongren City, the southern part of Qiannan Prefecture, and the northwestern part of Bijie City; (2) there are six main influencing factors in the three criterion layers, i.e., hydraulic engineering, emergency drought resistance, and social economy, and their contribution rates are as follows: surface water supply and storage rate > average number of soil moisture monitoring stations > per capita GDP > agricultural emergency drought irrigation rate > regional water supply assurance rate > cultivated land effective irrigation rate.

Spatiotemporal characteristics and obstacle factors identification of agricultural drought disaster risk: A case study across Anhui Province, China

Identifying the spatiotemporal characteristics and obstacle factors of the agricultural drought disaster risk is essential to reduce grain losses and ensure food security. However, due to the high uncertainty in drought disaster risk system, there are few effective risk evaluation and diagnosis methods. In this study, the uncertain information contained in sample data was mined and utilized, and a calculation method of the dynamic difference degree coefficients for the five-element connection number was proposed. Then, a quantitative risk evaluation and diagnosis model was established. Furthermore, the spatiotemporal characteristics and key obstacle factors of the agricultural drought disaster risk across Anhui Province, China from 2008 to 2017 were identified. The results indicated that the risk grades of the connection number values of North Anhui, Central Anhui, and South Anhui in 2008 were 0.359 (high risk), 0.072 (medium risk), and 0.097 (medium risk), respectively, and those in 2017 were 0.103 (medium risk), 0.196 (medium risk), and 0.368 (low risk), respectively. Thus, there were salient spatiotemporal characteristics in which the risk decreased from north to south and tended to decrease over time. In addition, the long-term high risk in North Anhui was due to the severe drought hazard, low forest cover, high exposure to drought, and low drought resistance capacity. The worse risk status in Central Anhui was caused by the small precipitation and water resources amount, low relative humidity, and large agricultural population. The factors inhibiting risk reduction in South Anhui were the large paddy field areas, low reservoir regulation and storage, and fewer water-saving irrigation areas. In summary, this method is effective and exhibits high sensitivity to risk change, and it can be applied to other grain production areas. The results can provide a scientific basis for formulating the targeted measures of agricultural drought disaster risk control in Anhui Province.

POTENSI RAINWATER HARVESTING DALAM MENGURANGI RISIKO KEKERINGAN DI KABUPATEN KARAWANG

<p class="Abstract"><em><span lang="EN-US">Drought occurs quite often in Indonesia, closely related to water availability for community needs. One of the districts in West Java Province experiencing drought problems is Karawang district, where the RWH (Rainwater Harvesting) concept will be applied. This study aimed to analyze the risk of drought-related to applying the potential RWH in reducing drought risk. This study only focuses on meteorological drought, determined by SPI (Standardized Precipitation Index). Identification of potential areas for the application of RWH is carried out using the Weighted Method Overlay approach in the Geographic Information System (GIS), which was modified by adding a parameter of potential drought hazard. The potential reliability of RWH, as seen from Volumetric Reliability (VR) for supplying the average water requirement of MCK (Bath Washing Toilet) per year, indicates that most of the Karawang district area is potential for applying RWH. The results of adding the potential drought hazard parameters on applying the RWH concept show the decreasing area of very potential and potential category areas into 5,38%, the increase of drought resistance capacity is 17.5%, and the risk-reducing to 8.3%. Those results are due to the changes in the area of drought in the risk analysis. The assumptions of 60 rainy days on the average rainy day in a year and all households making RWH storage systems were used in the analysis. The results of this study can be used as a first step to see the potential of RWH in Karawang Regency both in terms of area and reliability.</span></em></p>

Endocellulase SlGH9-21 significantly improves drought resistance and storage capacity of tomato

Drought, one of the most important abiotic factors affecting plant growth, causes a large reduction in tomato production every year. Tomato, a berry fruit and vegetable that can be eaten fresh or cooked, has rich nutritional value. However, most of ripe fruits show softening of pericarp, which leads to damage easily during transportation, and shorten the shelf life. Fruit mechanical strength is important to the texture, transport resistance and shelf life of tomato fruit. We found a natural tomato mutant in the field, which showed excellent drought resistance ability and late ripening characteristics. The target gene Solyc09g075360 (SlGH9-21) was obtained through transcriptome data screening. After the gene was silenced, tomatoes improved their drought resistance by reducing stomatal aperture and increasing stem vessel diameter. We also found that silencing of the SlGH9-21 gene delayed the ripening of tomato fruit and improved fruit firmness. Compared with the control, the ripening of the fruit of SlGH9-21 gene-silenced plants was delayed by approximately 10 days, which increased the fruit firmness and storage tolerance and reduced the water loss rate of fruit. Overall, the study of tomato stress response mechanisms and the identification of key genes regulating fruit hardness are beneficial to the improvement of tomato resistance. It is also conducive to the improvement of tomato quality. The research results can lay a foundation for the enhancement of fruit storage tolerance and stress resistance.

Drought response strategies are coupled with leaf habit in 35 evergreen and deciduous oak (Quercus) species across a climatic gradient in the Americas.

Distinct survival strategies can result from trade-offs in plant function under contrasting environments. Investment in drought resistance mechanisms can enhance survivorship but result in conservative growth. We tested the hypothesis that the widespread oaks (Quercus spp.) of the Americas exhibit an interspecific trade-off between drought resistance and growth capacity. Using experimental water treatments, we isolated adaptive trait associations among species in relation to their broad climates of origin and tested for correlated evolution between plant functional responses to water availability and habitat. Across all lineages, oaks displayed plastic drought responses - typically acclimating through osmolyte accumulation in leaves and/or employing conservative growth. Oaks from xeric climates had higher osmolytes and reduced stomatal pore area index, which allows for moderated gas exchange and limits tissue loss. Patterns suggest drought resistance strategies are convergent and under strong adaptive pressure. Leaf habit, however, mediates the growth and drought resistance strategies of oaks. Deciduous species, and evergreen species from xeric climates, have increased drought tolerance through osmoregulation, which allows for continuous, conservative growth. Evergreen mesic species show limited drought resistance but could enhance growth under well-watered conditions. Consequently, evergreen species from mesic environments are especially vulnerable to chronic drought and climate change.

System Structure–Based Drought Disaster Risk Assessment Using Remote Sensing and Field Experiment Data

With the impacts of climate change and human activities, agricultural drought disaster losses have increased remarkably. Drought disaster risk assessment is a prerequisite for formulating disaster reduction strategies and ensuring food security. However, drought disaster risk is a complex system, and quantitative assessment methods reflecting the risk formation mechanism are still rarely reported. This study presented a chain transmission system structure of drought disaster risk, which meant that drought disaster loss risk R was derived from drought hazard H by the transformation of drought disaster vulnerability V. Based on this point, firstly, a drought hazard curve between drought intensity and drought frequency was established using remote sensing data and the copula function. Then, a crop loss calculation approach under various drought events and drought resistance capacity scenarios was achieved by two-season field experiments and the AquaCrop model. Finally, a loss risk curve cluster of “drought frequency–drought resistance capacity–yield loss rate” was proposed by the composition of the above two quantitative relationships. The results of the case study for summer maize in Bengbu City indicated that the average yield loss rate under 19 droughts occurring during the growth period of maize from 1982 to 2017 was 24.51%. High risk happened in 1988, 1992, 1994, 2001, and 2004, with the largest loss rate in 2001, up to 65.58%. Overall, droughts with a return period less than two years occurred frequently during the growth period of summer maize in Bengbu, though the loss risk was still controllable. In conclusion, the results suggest that the loss risk curve provides a new effective method of drought disaster risk quantitative assessment from a physical mechanism perspective, which lays a scientific foundation for decision-making in risk management.

The effects of drought on stock prices: An industry-specific perspective

In this study, we examine the effect of drought on industry stock prices using a balanced panel of monthly data for 15 industries classified by China Securities Regulatory Commission in 2012. By combining the results of ordinary least squares (OLS) estimation and quantile regression models, we present a comprehensive evaluation of the relationship between drought and industry stock prices. The OLS regression results generally show that drought is negatively correlated with industry stock prices. However, quantile regression reveals that the effect of drought changes from positive to negative from the lowest to the highest stock price quantile. In addition, drought resistance capacity varies by industry. We further use threshold regression to determine the effects of investor sentiment on the relationship between drought and stock prices and identify two different regimes: low sentiment and high sentiment. In the low sentiment regime, drought has a significant negative effect on industry stock prices, while in the high sentiment regime, drought has a significant positive impact on industry stock prices.

Quantitative Evaluation and Obstacle Factor Diagnosis of Agricultural Drought Disaster Risk Using Connection Number and Information Entropy.

To promote the application of entropy concepts in uncertainty analysis of water resources complex system, a quantitative evaluation and obstacle factor diagnosis model of agricultural drought disaster risk was proposed using connection number and information entropy. The results applied to Suzhou City showed that the agricultural drought disaster risks in Suzhou during 2007–2017 were all in middle-risk status, while it presented a decreasing trend from 2010. The information entropy values of the difference degree item bI were markedly lower than those of the difference degree b, indicating that bI provided more information in the evaluation process. Furthermore, the status of drought damage sensitivity and drought hazard were improved significantly. Nevertheless, high exposure to drought and weak drought resistance capacity seriously impeded the reduction of risk. Thus, the key to decreasing risk was to maintain the level of damage sensitivity, while the difficulties were to reduce exposure and enhance resistance. In addition, the percentage of the agricultural population, population density, and percentage of effective irrigation area were the main obstacle factors of risk and also the key points of risk control in Suzhou. In short, the results suggest that the evaluation and diagnosis method is effective and conducive to regional drought disaster risk management.

Morphological and Physiological Responses of Melia azedarach Seedlings of Different Provenances to Drought Stress

Melia azedarach Linn. is a deciduous tree of the Melia genus in the Meliaceae family that is native to China. To study the mechanism of drought resistance in Melia azedarach and evaluate the drought resistance capacity of each provenance, we selected eight provenances (Shandong Kenli, Jiangsu Pizhou, Hubei Shayang, Jiangsu Xuanwu, Jiangxi Xihu, Jiangsu Jurong, Guangdong Luogang, and Henan Shihe) as the research subjects and set four levels of drought stress treatment (CK: 75% of field capacity, mild drought: 60% of field capacity, moderate drought: 45% of field capacity, and severe drought: 30% of field capacity). The results showed that the growth in the seedling height and the ground diameter, the leaf relative water content, transpiration rate (Tr), net photosynthetic rate (Pn), stomatal conductance (Gs), and the content of chlorophyll (Chl) decreased with the increasing stress levels, while the root–shoot ratio, water saturation deficit, and the contents of malondialdehyde (MDA) increased. The SOD in most provenances initially increased and then decreased, reaching a peak during moderate drought. At the late stage of treatment, the magnitude of the changes in the photosynthetic indicators was more pronounced than in the physiological indicators. Principal component analysis showed that the contribution of all four principal components under the three drought stresses was above 85%, which represented the majority of the original data. Combined with the affiliation function method and weights, the comprehensive evaluation value (D value) of the drought resistance was calculated for the eight provenances. Then, we obtained the order of drought resistance of the test materials under the three drought stresses, respectively. The combined results revealed that the drought resistance of Henan Shihe and Jiangxi Xihu was stronger, while the drought resistance of Guangdong Luogang and Hubei Shayang was weaker. Based on the above findings, we can select provenances with strong and weak drought resistance for transcriptome sequencing to screen drought-resistant genes for an in-depth study at the molecular level.

Lianas and Trees From a Seasonally Dry and a Wet Tropical Forest Did Not Differ in Embolism Resistance but Did Differ in Xylem Anatomical Traits in the Dry Forest

One of the most prominent changes in neotropical forests has been the increase in abundance and size of lianas. Studies suggest that lianas have more acquisitive strategies than trees, which could allow them to take advantage of water more effectively when it is available in water-limited forests, but few studies compared across growth form (i.e., lianas vs. trees) and forest type (i.e., wet vs. seasonally dry). We measured hydraulic and anatomical traits of co-occurring lianas and trees that convey drought resistance (xylem embolism resistance and intervessel pit membranes) and water transport capacity (xylem vessel diameter and density) in a seasonally dry and a wet evergreen tropical forest to address: (1) Are there differences between vulnerability to embolisms (P50—water potential at 50% loss of hydraulic conductivity) and hydraulic safety margins (HSM) across growth form and forest type? (2) How do vessel diameter and density vary across growth form and forest type? (3) Are there differences in xylem intervessel pit membrane thickness across growth form and forest type and does it predict xylem embolism vulnerability in trees and lianas? We examined hydraulic and xylem anatomical traits of 32 species—eight lianas and eight trees in each forest type. We found no difference in P50and HSMs between lianas and trees and between the wetter and drier forest. Dry forest lianas had 81% greater maximum vessel diameter and 125% greater range in vessel diameter sizes than dry forest trees but, there was no significant difference between life forms in the wet forest. Dry forest species had 50% greater vessel density and 30% greater maximum pit membrane thickness than wet forest ones. Maximum pit membrane thickness was correlated to P50and HSMs. The main difference between lianas and trees occurred in the dry forest, where lianas had larger maximum xylem vessel size than trees, implying that they have proportionally greater hydraulic conductive capacity than the trees in seasonal forests.

Evidence for evolution and selection of drought-resistant genes based on high-throughput resequencing in weedy rice.

Weedy rice (Oryza sativa f. spontanea) is a relative of cultivated rice that propagates in paddy fields and has strong drought resistance. In this study, we used 501 rice accessions to reveal the selection mechanism of drought resistance in weedy rice through a combination of selection analysis, genome-wide association studies, gene knockout and overexpression analysis, and Ca2+ and K+ ion flux assays. The results showed that the weedy rice species investigated have gene introgression with cultivated rice, which is consistent with the hypothesis that weedy rice originated from de-domestication of cultivated rice. Regions related to tolerance have particularly diversified during de-domestication and three drought-tolerance genes were identified. Of these, Os01g0800500 was also identified using an assay of the degree of leaf withering under drought, and it was named as PAPH1, encoding a PAP family protein. The drought-resistance capacity of PAPH1-knockout lines was much lower than that of the wild type, while that of overexpression lines was much higher. Concentrations of Ca2+ and K+ were lower in the knockout lines and higher in the overexpression lines compared with those of the wild type, suggesting that PAPH1 plays important roles in coping with drought stress. Our study therefore provides new insights into the genetic mechanisms underlying adaptive tolerance to drought in wild rice and highlights potential new resistance genes for future breeding programs in cultivated rice.

Important Physiological Changes Due to Drought Stress on Oat

As temperatures rise and water availability decreases, the water decit is gaining attention regarding future agricultural production. Drought stress is a global issue and adversely affects the productivity of different crops. In this study, drought-tolerant varieties of oats were screened to determine drought-tolerant varieties that may be employed in drought-prone areas to achieve sustainable development and mitigate the impact of climate change. To do so, the growth and stress adaptive mechanism of 15 domestic and overseas oat cultivars at the seedling stage were analyzed. Water stress was simulated using 20% polyethylene glycol (PEG-6000). The results showed that the soluble protein content and superoxide dismutase activity of variety DY2 significantly increased under drought stress, whereas the photochemical efficiency and relative water content decreased slightly. The relative electrical conductivity (REC) and drought damage index of the QH444 and DY2 varieties increased the least. The peroxidase content of Q1 and DY2 significantly increased, and the catalase activity of Q1, QH444, and DY2 also substantially increased. Principal component analysis revealed that nine physiological and biochemical parameters were transformed into three independent comprehensive indexes. The comprehensive evaluation results showed that DY2, LN, and Q1 exhibited a strong drought resistance capacity and could be used as a reference material for a drought-resistant oat breeding program. The gray correlation analysis also indicated that Fv/Fm, chlorophyll, REC, and malondialdehyde could be used as key indexes for evaluating the drought resistance of oat.

Risk evaluation of agricultural drought disaster using a grey cloud clustering model in Henan province, China

Frequent drought is a critical limiting factor for regional agriculture development. Accurately evaluating regional agricultural drought risk contributes to raising disaster risk management and reducing drought disaster losses. This paper proposes a grey cloud clustering model based on panel data to assess the agricultural drought disaster risk of Henan province. The new model includes two parts. One component is indicator and time weights determination which uses the grey incidence analysis methods, the maximum deviation and maximum entropy principle, respectively. The other part is the construction of grey cloud possibility function which calculates the drought disaster risk grade. Then, the proposed model is applied for assessing the agricultural drought disaster risk of Henan Province at the regional scale, and the time scale selected is from 2012 to 2016. The agricultural drought disaster presents different spatial distribution in drought hazard, exposure, damage sensitivity and drought resistance capacity. The comprehensive risk evaluation results indicate that the drought risk in the most northern and southern regions of Henan Province is lower, while the western, mid-western and eastern regions have a higher risk. Compared with the traditional assessment models for disaster risk, the proposed model can recognize the random, fuzzy and grey uncertainties of the agricultural drought disaster system. Thus, it is a beneficial tool for drought disaster risk assessment and can help to make some suggestions for drought disaster mitigation.

Hydrological Drought Regimes of the Huai River Basin, China: Probabilistic Behavior, Causes and Implications

: Hydrological droughts were characterized using the run-length theory and the AIC (Akaike information criterion) techniques were accepted to evaluate the modeling performance of nine probability functions. In addition, the copula functions were used to describe joint probability behaviors of drought duration and drought severity for the major tributaries of the Huai River Basin (HRB) which is located in the transitional zone between humid and semi-humid climates. The results indicated that: (1) the frequency of hydrological droughts in the upper HRB is higher than that in the central HRB, while the duration of the hydrological drought is in reverse spatial pattern. The drought frequency across the Shiguan River along the south bank of the HRB is higher than the other two tributaries; (2) generalized Pareto distribution is the appropriate distribution function with the best performance in modelling the drought duration over the HRB; while the Generalized Extreme Value (GEV) distribution can effectively describe the probabilistic properties of the drought severity. Joe copula and Tawn copula functions are the best choices and were used in this study. Given return periods of droughts of <30 years, the droughts in the upper HRB are the longest, and the shortest are in the central HRB; (3) the frequency of droughts along the mainstream of the HRB is higher than tributaries of the HRB. However, concurrence probability of droughts along the mainstream of the HRB is lower than the tributaries of the HRB. The drought resistance capacity of HRB has been significantly improved, effectively reducing the impact of hydrological drought on crops after 2010.

Effects of biochar addition on soil hydraulic properties before and after freezing-thawing

Biochar as a soil amendment has attracted wide attention worldwide. However, the study of biochar on soil hydraulic properties during freeze-thawing remains insufficient. The purpose of this study was to determine the effect of straw biochar on soil water retention and soil hydraulic conductivity during a freeze-thaw period. Specifically, the effects of different biochar application rates (0, 30, 60, 90 and 120 t·hm−2) on the soil water characteristic curve (SWRCs), saturated hydraulic conductivity (Ksat) and hydraulic characteristic parameters were analysed through field trials. The response relationship between changes in the soil pore size and hydraulic characteristics was explored. The results showed that the combination of biochar amendment and freezing-thawing significantly increased the soil micro pore size (≥0.3–5 μm), soil voids (>100 μm) and total porosity (TP) and thereby improved the soil water retention capacity during the melting period. In addition, the use of biochar can promote the Ksat before and after freezing-thawing. However, increases in the carbon added during the melting period decreased the value of Ksat by 3.89%, 8.12%, 13.02% and 18.14% (p < 0.05) due to blockage of the soil pores by fine carbon particles. Compared with the control treatment, biochar significantly increased the field capacity (FC) and available water content (AWC) in soil. The largest relative change in the FC was obtained with an applied carbon amount of 60 t·hm−2, and this effect would improve the drought resistance capacity of the soil in the spring season. The excessive application of biochar led to an imbalance between the liquid and gas phases in soil, and thus, suggested biochar should not be applied in excess amounts to avoid negative effects on the soil structure. This study revealed the response mechanism of the hydraulic characteristics of the carbon-soil mixture during the freeze-thaw period and can provide a reference for the efficient utilization of soil water resources and the prediction of soil moisture in cold and dry areas.

Kaolin particle film modulates morphological, physiological and biochemical olive tree responses to drought and rewatering

Regarding the foreseeing climate change is reasonable to expect harmful consequences to olive tree (Olea europaea L.), an iconic species of Mediterranean region. Thus, the selection of practices that allow a better drought resistance and recovery capacity needs the immediate attention of scientific community. This study evaluates the strategies adopted by young potted olive trees, subjected to three cycles of drought and rewatering, in the presence of a reflective clay, kaolin (KL). The results demonstrated that KL induced shade-related leaf structural changes and was effective in keeping leaf water status during the most stressful periods. In general, photosynthetic activity of sprayed plants was improved by the alleviation of drought-induced stomatal and non-stomatal limitations. Moreover, during stress imposition sprayed leaves showed reduced oxidative damages, allowing lower investment in antioxidant defences. Furthermore, sprayed plants also had lower nighttime water losses due to inferior nighttime stomatal conductance, and are able to maintain higher respiration rates. Upon rewatering, the shaded effect conferred by KL limited gas exchange restauration, but improved the plants’ capacity to restore the metabolic functions. In spite of the induced physiological and biochemical changes, no significant differences were found in whole-plant water use efficiency and plant biomass accumulation, possibly by the attenuation of photosynthesis restauration during the recovery events. In conclusion, the changes induced by KL might be beneficial under severe conditions, as on realistic Mediterranean field environments.

Assessing the drought mitigation ability of the reservoir in the downstream of the Yellow River

Due to climate change and human activities, drought frequency and its corresponding impact have intensified in many regions across China. Reservoirs are key in regulating streamflow and mitigating a drought's impact. Therefore, it is vital to analyze their drought mitigation ability. In this study, the drought adaptation capacity and drought resistance capacity of the reservoir are selected as two drought mitigation ability metrics to measure the effectiveness of a reservoir when facing a drought. The drought adaptation capacity represents the ability of a reservoir to prevent and mitigate damage caused by drought. It is assessed from two viewpoints, one reflecting the reservoir scale and layout reasonability, while the second reflecting the engineering operation and management. The drought resistance capacity refers to the ability of a reservoir to meet the water demand under a certain level of a drought (i.e. drought joint return period, which is defined later), and is calculated based on the reservoir's water supply and water demand. These two drought mitigation ability metrics can be applied not only for a single reservoir, but also for a group of reservoirs. This study applies these two metrics in the downstream of the Yellow River for a group of reservoirs. The results show that: 1) the ability of reservoirs in the downstream of the Yellow River for prevention and mitigation of damage caused by drought rates in the normal grade; and 2) the reservoirs can better resist the drought whose joint return period is smaller than 2 years while the drought resistance capacity is weak when the joint return period is over 6 years. Overall, the basin's drought adaptation and resistance capacity need to be improved. Management and operation of current water conservancy projects still need to be enhanced.

Alginate-derived oligosaccharides promote water stress tolerance in cucumber (Cucumis sativus L.)

Marine alginate-derived oligosaccharides (ADOs) are prepared from degraded alginate. Our experiments were carried out to determine the mechanism of ADOs to improve resistance to water stress in cucumber (Cucumis sativus L.). We evaluated the effects of ADOs on physiological indices, photosynthesis, reactive oxygen species (ROS) levels, antioxidant enzyme activities, and relative expression levels of drought resistance genes. The growth of drought stressed cucumber decreased markedly. However, treatment with ADOs significantly improved the diameter, fresh weight, photosynthetic rate, transpiration rate, stomatal conductance, maximum quantum yield of photosystem II (Fv/Fm) and chlorophyll degradation; thus, reversing the effects of drought stress. Moreover, the antioxidant levels and ROS scavenging enzyme activities also increased in response to the ADOs. Additionally, the genes involved in abscisic aid (ABA) signaling and the drought stress response, such as superoxide dismutase [Cu-Zn] (CsSOD(Cu-Zn)), the peroxidase superfamily protein (CsPOD3), ABA deficient 2 (CsABA2), responsive to ABA 18 (CsRAB18), abscisic acid insensitive 5 (CsABI5), responsive to dehydration 22 (CsRD22), and responsive to dehydration 29A (CsRD29A) were upregulated by ADOs. The ABA content was also improved by ADOs. Our results suggest that ADOs induced the expression of some antioxidant enzyme synthetic genes involved in the ABA signaling pathway by stimulating ABA synthesis to improve the drought resistance capacity in cucumber.