Plant Water Relations Research Articles

Use limitation on soil water resource by red plum apricot

Since 1995, the yield, benefits, and plantation area of red plum apricot have increased dramatically. But as red plum apricot trees’ canopy and roots grew, soil drying appeared and sometimes become severe in a wet year. The severe soil drying influence the yield, quality and benefits of red plum apricot because precipitation is small and with a big season change. At this time, the plant-water relationship has to be regulated on Soil Water Resource Use Limitation by Plant and Soil Moisture Vegetation Carrying Capacity. However, there are few studies on the utilization limit of soil water resources by red plum apricot forest land. In this study, daily precipitation, and soil water suctions at different soil water content are measured, and the maximal infiltration depth and the soil water resource use limitation by red plum apricot were estimated. The results show that wilting coefficient varies with soil depth from 7.98 in surface soil to 7.1% in 240 cm soil depth, the maximal infiltration depth is 290 cm and the Use Limit of Soil Water Resources by red plum apricot is 212.7 mm. When the soil water resource in the maximal infiltration depth is lower than the limit, the regulation of the plant-water relationship must be considered.

Further Test of Pneumatic Method in Constructing Vulnerability Curves Using Six Tree Species with Contrasting Xylem Anatomy

The pneumatic method is a novel method determining vulnerability to embolism in plants, yet it remains unclear whether this method is suitable for all species with different xylem anatomy. In this study, using six tree species with contrasting xylem anatomy, including four vessel-bearing species (diffuse-porous wood and ring-porous wood) and two tracheid-bearing species (non-porous wood), we test the reliability of the pneumatic method by comparing to hydraulic methods and also considering turgor loss point and native embolism. Vessel length distribution and cut-open vessel volume were also evaluated using the silicone injection technique. Additionally, we also synthesized published data to find out the consistency between the pneumatic method and hydraulic methods. Results showed that there was a maximum 10-folds difference in mean vessel length and mean vessel diameter varying from 30 to 56 μm among species. The estimated open vessel volume ranges from 0.064 to 0.397 mL, with a maximum of 14% of the tube vacuum reservoir. For four vessel-bearing species, the pneumatic method showed good consistency with hydraulic methods, and this consistency was evidenced by turgor loss point and native embolism. For two tracheid-bearing species, the pneumatic method significantly overestimated vulnerability because of the bad consistencies with hydraulic methods and plant water relations. Data synthesis of 56 species also suggested that the pneumatic method can accurately measure the embolism vulnerability of vessel-bearing species but not for tracheid-bearing species. Our study provided further evidence that the pneumatic method is accurate for most vessel-bearing species and thus has the potential to be widely used in the plant hydraulics field. However, we proposed that the precise calculation of air discharge volume should take into account the volume of open vessels for species with wide and long vessels.

Field Investigation into Tree Fates from Recent Apple Tree Decline: Abrupt Hydraulic Failure Versus Gradual Hydraulic Loss

In the last decade, a sporadic tree health syndrome affecting high-density apple plantings in North America has become known as Rapid Apple Decline (RAD) or Sudden Apple Decline (SAD). The affected apple trees were typically grafted on small dwarfing rootstocks, often displayed necrosis at the graft union, and suffered from sudden mortality that occurred over 2–3 weeks amid the growing season or a gradual decline. In 2019 and 2020, we conducted a multi-site investigation in the south Okanagan, British Columbia, Canada, to assess the stem hydraulic characteristics, stomatal conductance, leaf δ13C‰, and fruit dry matter accumulation of the declining trees during disease progression. In trees that died, mortality appeared to be associated with severe disruption in xylem water transport at the damaged graft union, followed by abrupt hydraulic failure. In contrast, symptomatic trees that did not die exhibited the moderately declined plant water relations and a reduction in fruit dry matter accumulation followed by either further deterioration or eventual recovery. This pattern indicates the risk of carbohydrate depletion over gradual hydraulic decline and the importance of timely horticultural remedies. In the present study, we discuss potential horticultural practices to mitigate hydraulic dysfunctions and enhance crop tolerance.

Evaluation of the Effect of Water Stress on Clonal Variations of Cv. Monastrell (Vitis vinifera L.) in South-Eastern Spain: Physiology, Nutrition, Yield, Berry, and Wine-Quality Responses

The present study aims to analyze the physiological and agronomical response to drought among seven local and traditional field-grown Monastrell clones (4, 94, 188, 360, 276, 372, and 373) over four seasons (2018–2021) under optimum irrigation conditions (control) and water stress (stress). We have focussed on measuring Monastrell interclonal variability in plant water relations and leaf gas exchange, vegetative growth, leaf mineral nutrition, yield, water use efficiency (WUE), and grape and wine quality. A classification of the different clones according to drought-tolerance degree and agronomical/oenological performance was established. The classification revealed that (a) The most drought-tolerant clone (i.e., clone 4) was neither the most productive (8600 kg ha−1), the most efficient in terms of water use (average of 25 kg m−3), nor the one that presented a better grape quality; (b) The most productive and efficient clone (i.e., clone 94) (11,566 kg ha−1, average of 30 kg m−3) was also a drought-tolerant clone, but it provided the worst berry and wine qualities with the lowest aromatic/nutraceutical potential, and it is not recommended for premium red wine production; (c) Conversely, clone 360 provided the highest berry quality, but at the expense of a greatly reduced vigor and yield (4000 kg ha−1) and a lower WUEyield (average of 10 kg m−3); (d) Low-vigor clones 372 and 276 were the most sensitive to drought conditions and put more water conservation mechanisms into play, i.e., a tighter control of vine water use and reduced leaf transpiratory surface, under soil water deficit and high vapor pressure deficit (VPD). In addition, these clones reached a balance between drought tolerance, productive water use efficiency (WUEyield), and berry and wine quality, because they provided moderate yields (7400–7700 kg ha−1), a high WUEyield (average between 17–19 kg m−3 applied water), and an enhanced berry and wine quality with greater oenological, nutraceutical, and aromatic potential; (e) High-vigor clone 188 also displayed several mechanisms of drought tolerance (tighter stomatal control of water use), maintained a higher yield (10,500 kg ha−1) and a very high WUEyield (29 kg m−3), enhanced berry quality (similarly to 276 or 372), and improved oenological/aromatic potential, and can also be recommended for the application of low water volume deficit irrigation (DI) strategies under semi-arid conditions.

Consistent responses to moisture stress despite diverse growth forms within mountain fynbos communities

Understanding climate change impacts on the Cape Floristic Region requires improved knowledge of plant physiological responses to the environment. Studies examining physiological responses of mountain fynbos have consisted of campaign-based measurements, capturing snapshots of plant water relations and photosynthesis. We examine conclusions drawn from prior studies by tracking in situ physiological responses of three species, representing dominant growth forms (proteoid, ericoid, restioid), over 2 years using miniature continuous sap flow technology, long-term observations of leaf/culm water potential and gas exchange, and xylem vulnerability to embolism. We observed considerable inter-specific variation in the timing and extent of seasonal declines in productivity. Shallow-rooted Erica monsoniana exhibited steep within-season declines in sap flow and water potentials, and pronounced inter-annual variability in total daily sap flux (Js). Protea repens showed steady reductions in Js across both years, despite deeper roots and less negative water potentials. Cannomois congesta—a shallow-rooted restioid—was least negatively impacted. Following rehydrating rain at the end of summer, gas exchange recovery was lower in the drier year compared with the normal year, but did not differ between species. Loss of function in the drier year was partially accounted for by loss of xylem transport capacity in Erica and Cannomois, but not Protea. Hitherto unseen water use patterns, including inter-annual variability of gas exchange associated with contrasting water uptake properties, reveal that species use different mechanisms to cope with summer dry periods. Revealing physiological responses of key growth forms enhances predictions of plant function within mountain fynbos under future conditions.

Effect of Bacterial Strains with Different Ability to Synthesize Auxins and Cytokinins on the Growth and Water Relations of Wheat Plants

The content of cytokinins, auxins, chlorophyll, transpiration, content and relative content of water, water and osmotic potentials, hydraulic conductivity, morphological parameters of durum wheat (Triticum durum Desf.) plants after the introduction into their rhizosphere of cytokinin-producing strains (Bacillus subtilis IB-22) or auxin-producing (Pseudomonas mandelii IB-Ki14) bacteria was evaluated. The experiments were carried out in laboratory conditions in vessels with agrochernozem at an optimal level of illumination. It was shown that the cytokinin-producing strain stimulated plant growth, accumulation of chlorophyll, and increased transpiration to a greater extent compared to plants treated with the auxin-producing strain. Plants under the influence of the B. subtilis IB-22 strain lost more water during transpiration, while there was no decrease in the level of water content and turgor. It is concluded that bacterial cytokinins affect the water metabolism of wheat plants by increasing hydraulic conductivity, and bacterial auxins - to a greater extent due to osmotic regulation. A more significant stimulation of plant growth by bacteria of the B. subtilis IB-22 strain is also explained by the ability of cytokinins to influence the chlorophyll content to a greater extent than auxins.

Effects of water and salt stresses on plant growth and xylem hydraulic properties of tomato.

Xylem is the main tissue for water transport in plants, and the changes of hydraulic properties in which would affect plant water relations and fruit water accumulation. It remains unclear regarding the responses of xylem anatomy and hydraulic properties to water and salt stresses in tomato plants and their relationships with plant growth and fruit water content. We conducted a pot experiment in a greenhouse to investigate the responses of plant growth, fruit water content, and xylem hydraulic properties of a cherry tomato (Hong Baoshi) and a medium-fruited tomato (Beifan 501). There were three treatments, control with a soil water content (θ) of 75%-95% of field capacity (FC) and an initial electrical conductivity (EC) of 0.398 dS·m-1; water stress with θ of 75%-95% of FC (before flowering) and 45%-65% of FC (from flowering until maturity) and an EC of 0.398 dS·m-1; and salt stress with θ of 75%-95% of FC and an EC of 1.680 dS·m-1. Results showed that water and salt stresses decreased the cross-sectional stem area and xylem vessel diameter by 22.0%-40.7% and 10.0%-18.3%, respectively, and reduced the specific hydraulic conductivity of stem and the hydraulic conductivity of peduncle by 8.8%-41.1% and 12.9%-28.4%, respectively. Those changes inhibited plant growth and reduced aboveground fresh weight, fruit size, fresh weight and water content, with a more pronounced negative effect in the medium-fruited tomato. More-over, fruit water content was positively correlated with the specific hydraulic conductivity of stem and peduncle. In conclusion, water and salt stresses would inhibit plant growht, fruit fresh weight, and consequently tomato yield, due to their negative effects on xylem hydraulic properties of the tomato plant. Medium-fruited tomatoes are more susceptible to water and salt stresses than cherry tomatoes.

Comparing water use patterns of sand‐binding species in an alpine semi‐arid desert

AbstractThe processes of species obtaining water resources are crucial to evaluate the adaptability of plantations, which can affect the establishment and survival of restored ecosystems and functions of water‐limited ecosystems. However, there are still limitations in understanding water use patterns of different four plantations (Populus sylvestris, Salix cheliophe, Hippophae rhamnoides and Artemisia ordosica) in the Qinghai Lake basin. Stable isotopes of xylem water of four individual species were analysed at different dunes located at the eastern shore of Qinghai Lake in 2018 and 2019. The purpose of this study was to explore potential water sources used by different life form plants, to identify whether the soil moisture content and root distribution determined the plants water use patterns. Results from the Bayesian mixing model MixSIAR showed that all species mainly uses three levels of soil water, but they extracted soil water from different layers in different growing seasons among species. All species primarily depended on water from upper soil layers at the early growing stage, but P. sylvestris and S. cheliophe also absorbed much proportion middle and deep soil layers' water in dry year of 2019. All four species shift to use middle or deep soil layer water rather than shallow water in July with the most rainfall and soil water content (SWC). However, it was only used by P. sylvestris and H. rhamnoides in 2018. In all, seasonal water use pattern of different species was affected by SWC, soil texture and root distribution. Compared with moratorium plantations such as S. cheliophe, mixed afforestation of P. sylvestris and H. rhamnoides maximized of soil water sources absorbed by the plants. The study can shed light on plant–water relationships to facilitate the woody species for afforestation and desertification restoration management in the semi‐arid desert ecosystem.

Positive community effects of nurse-plant shrubs along a tropical alpine elevation gradient: are they linked with plant water relations?

Positive community effects of nurse-plant shrubs along a tropical alpine elevation gradient: are they linked with plant water relations?

Foliar water uptake improves branch water potential and photosynthetic capacity in Calligonum mongolicum

Atmospheric water is among the most important water sources for plants in arid ecosystems and plays an important role in facilitating drought stress survival in plants. However, little is known about the specific physiological benefits of foliar water uptake (FWU) for woody plants inhabiting arid desert areas. The objective of this study was to explore the physiological responses of Calligonum mongolicum to atmospheric water uptake by the assimilating branches, with a special focus on the FWU effect on shoot water status and photosynthesis. To this end, the canopies of natural C. mongolicum plants in a desert region of northwestern China were humidified in a field in-situ misting experiment and a long-term wetting experiment, during which physiological measurements of plant water relations and photosynthetic capacity were performed, alongside the observation of FWU by H218O isotopic tracing. Following the in-situ misting experiment, the water potential of the assimilating branches was significantly higher than that of the secondary branches at midnight, suggesting that FWU resulted in a reverse water potential gradient in C. mongolicum at the branch level. The 18O isotope was markedly enriched in the assimilating branches, secondary branches, and trunk xylem following the foliar uptake of 18O labeled water, indicating that the water uptake from the atmosphere by the assimilating branches could replenish the stem. The relative water content and water potential of the assimilating branches were significantly increased by FWU. The net photosynthetic rate, stomatal conductance, and maximum photochemical efficiency of C. mongolicum plants were markedly increased following the wetting treatment. Our results clearly show that C. mongolicum is capable of FWU, and that the absorbed water could be transported downward through the xylem and improve the branch water status and photosynthetic capacity. These findings provide a new perspective for deepening our understanding of the drought survival mechanism of plants in arid environments.

Transcriptomic Analysis of Distal Parts of Roots Reveals Potentially Important Mechanisms Contributing to Limited Flooding Tolerance of Canola (Brassica napus) Plants.

Since most of the root metabolic activities as well as root elongation and the uptake of water and mineral nutrients take place in the distal parts of roots, we aimed to gain insight into the physiological and transcriptional changes induced by root hypoxia in the distal parts of roots in canola (Brassica napus) plants, which are relatively sensitive to flooding conditions. Plants were subject to three days of root hypoxia via lowering oxygen content in hydroponic medium, and various physiological and anatomical features were examined to characterize plant responses. Untargeted transcriptomic profiling approaches were also applied to investigate changes in gene expression that took place in the distal root tissues in response to hypoxia. Plants responded to three days of root hypoxia by reducing growth and gas exchange rates. These changes were accompanied by decreases in leaf water potential (Ψleaf) and root hydraulic conductivity (Lpr). Increased deposition of lignin and suberin was also observed in the root tissues of hypoxic plants. The transcriptomic data demonstrated that the effect of hypoxia on plant water relations involved downregulation of most BnPIPs in the root tissues with the exception of BnPIP1;3 and BnPIP2;7, which were upregulated. Since some members of the PIP1 subfamily of aquaporins are known to transport oxygen, the increase in BnPIP1;3 may represent an important hypoxia tolerance strategy in plants. The results also demonstrated substantial rearrangements of different signaling pathways and transcription factors (TFs), which resulted in alterations of genes involved in the regulation of Lpr, TCA (tricarboxylic acid) cycle-related enzymes, antioxidant enzymes, and cell wall modifications. An integration of these data enabled us to draft a comprehensive model of the molecular pathways involved in the responses of distal parts of roots in B. napus. The model highlights systematic transcriptomic reprogramming aimed at explaining the relative sensitivity of Brassica napus to root hypoxia.

Evidence for phylogenetic signal and correlated evolution in plant-water relation traits.

Evolutionary relationships are likely to play a significant role in shaping plant physiological and structural traits observed in contemporary taxa. We review research on phylogenetic signal and correlated evolution in plant-water relation traits, which play important roles in allowing plants to acquire, use, and conserve water. We found more evidence for a phylogenetic signal in structural traits (e.g. stomatal length and stomatal density) than in physiological traits (e.g. stomatal conductance and water potential at turgor loss). Although water potential at turgor loss is the most-studied plant-water relation trait in an evolutionary context, it is the only trait consistently found to not have a phylogenetic signal. Correlated evolution was common among traits related to water movement efficiency and hydraulic safety in both leaves and stems. We conclude that evidence for phylogenetic signal varies depending on: the methodology used for its determination, that is, model-based approaches to determine phylogenetic signal such as Blomberg's K or Pagel's λ vs statistical approaches such as ANOVAs with taxonomic classification as a factor; on the number of taxa studied (size of the phylogeny); and the setting in which plants grow (field vs common garden). More explicitly and consistently considering the role of evolutionary relationships in shaping plant ecophysiology could improve our understanding of how traits compare among species, how traits are coordinated with one another, and how traits vary with the environment.

Breeding Strategies for Drought Tolerance in Crop Plant, A View

Drought is one of the most severe abiotic stresses in many regions of the world, and it is one of the most urgent issues in the current climate scenario. Drought-tolerant varieties are in high demand, which appears to be a challenging task for plant breeders. However, difficulties are complicated by crop production challenges on genetic and physiological bases. Drought is one of the most major environmental factors affecting crop productivity and quality around the world. Drought mostly impacts crops that thrive in wetland conditions, which account for 80% of all farmed land in the world. Climate change raises the likelihood of increased drought in many regions of the world in the next decades, causing crop damage as a result of abnormal metabolism and perhaps reducing crop growth, crop death, or crop development death. Drought resistance is defined as the mechanism(s) that cause the crop to lose the least amount of yield in a drought environment compared to the highest yield in a constant-free of optimal environment. Drought stress reduces the size of the leaves, stem extension, and root proliferation inside the soil; it also disrupts plant water relations and reduces water-use efficiency, reducing the plant’s yielding ability. Therefore, breeding for drought resistance is a good approach, combining both conventional and molecular approaches to develop a drought resistant variety. Root morphology research, proline estimates, and leaf rolling are all factors to take into account. Breeding improved drought-tolerant cultivars may be more effective if selection is based on a comprehensive approach to testing. Water stress also affects the crop’s physiological activity by inhibiting photosynthesis and assimilates consumption in the growing leaves. Plant hormones play a key role in transducing the stress signal, with abscisic acid (ABA) being the most important among them. To alleviate suitable crop productivity under environmental stresses, scientists developed various breeding strategies, such as conventional breeding, which works for both self-pollinated and cross-pollinated crops and is used to develop or improve cultivars using a basic conservative tool for manipulating plant genomes within the natural genetic boundaries of species. Pedigree, recurrent selection, back-crossing, and mutation breeding are among the conventional breeding strategies used to generate cultivars that can withstand drought stress.

Genome-Wide Identification and Expression Analysis of the Aquaporin Gene Family in Lycium barbarum during Fruit Ripening and Seedling Response to Heat Stress.

Plant-water relations mediated by aquaporins (AQPs) play vital roles in both key plant growth processes and responses to environmental challenges. As a well-known medicinal and edible plant, the harsh natural growth habitat endows Lycium plants with ideal materials for stress biology research. However, the details of their molecular switch for water transport remain unclear. In the present work, we first identified and characterized AQP family genes from Lycium (L.) barbarum at the genome scale and conducted systemic bioinformatics and expression analyses. The results showed that there were 38 Lycium barbarum AQPs (LbAQPs) in L. barbarum, which were classified into four subfamilies, including 17 LbPIP, 9 LbTIP, 10 LbNIP, and 2 LbXIP. Their encoded genes were unevenly distributed on all 12 chromosomes, except chromosome 10. Three of these genes encoded truncated proteins and three genes underwent clear gene duplication events. Cis-acting element analysis indicated that the expression of LbAQPs may be mainly regulated by biotic/abiotic stress, phytohormones and light. The qRT-PCR assay indicated that this family of genes presented a clear tissue-specific expression pattern, in which most of the genes had maximal transcript levels in roots, stems, and leaves, while there were relatively lower levels in flowers and fruits. Most of the LbAQP genes were downregulated during L. barbarum fruit ripening and presented a negative correlation with the fruit relative water content (RWC). Most of their transcripts presented a quick and sharp upregulation response to heat stress following exposure of the 2-month-old seedlings to a 42 °C temperature for 0, 1, 3, 12, or 24 h. Our results proposed that LbAQPs were involved in L. barbarum key development events and abiotic stress responses, which may lay a foundation for further studying the molecular mechanism of the water relationship of Lycium plants, especially in harsh environments.

Foliar water uptake in Pinus species depends on needle age and stomatal wax structures.

Foliar water uptake (FWU) has been documented in many species and is increasingly recognized as a non-trivial factor in plant-water relationships. However, it remains unknown whether FWU is a widespread phenomenon in Pinus species, and how it may relate to needle traits such as the form and structure of stomatal wax plugs. In this contribution, these questions were addressed by studying FWU in current-year and 1-year-old needles of seven Pinus species. We monitored FWU gravimetrically and analysed the needle surface via cryo-scanning electron microscopy. Additionally, we considered the effect of artificial wax erosion by application of the surfactant Triton X-100, which is able to alter wax crystals. The results show for all species that (1) FWU occurred, (2) FWU is higher in old needles compared to young needles and (3) there is substantial erosion of stomatal wax plugs in old needles. FWU was highest in Pinus canariensis, which has a thin stomatal wax plug. Surfactant treatment enhanced FWU. The results of this study provide evidence for (1) widespread FWU in Pinus, (2) the influence of stomatal wax plugs on FWU and (3) age-related needle surface erosion.

Prospecting the Resilience of Several Spanish Ancient Varieties of Red Grape under Climate Change Scenarios.

Climate change results in warmer air temperatures and an uncertain amount and distribution of annual precipitations, which will directly impact rainfed crops, such as the grapevine. Traditionally, ancient autochthones grapevine varieties have been substituted by modern ones with higher productivity. However, this homogenization of genotypes reduces the genetic diversity of vineyards which could make their ability to adapt to challenges imposed by future climate conditions difficult. Therefore, this work aimed to assess the response of four ancient grapevine varieties to high temperatures under different water availabilities, focusing on plant water relations, grape technological and phenolic maturity, and the antioxidant capacity of the must. The study was conducted on fruit-bearing cuttings grown in pots in temperature-gradient greenhouses. A two-factorial design was established where two temperature regimes, ambient and elevated (ambient + 4 °C), were combined with two water regimes, full irrigation and post-veraison deficit irrigation, during fruit ripening. There were significant differences among the ancient varieties regarding plant water relations and fruit quality. This research underlines the importance of evaluating the behavior of ancient grapevine varieties that could offer good options for the adaptation of viticulture to future climate conditions.

Forest restoration and Sustainable of Soil Water Resources and High-quality sustainable management

Along with economic development and an increase in population, there is an increasing demand for goods such as timber, food, medicine, and so on, and ecological services such as fresh water and the environment. Because goods and service produced by the original forest cannot meet the increasing need of people, so most of the original forest has become farmland, plantation, and grass, and a lot of exotic plants was introduced to produce special products and service. As introduced plants grow, vegetation decline and crop failure happen in dry years or resource waste in wet years. In order to solve these problems, Years of theoretical research and investigation in fixed positions have shown that there is a soil water resources use limit by plants and the soil water vegetation carrying capacity in the process of vegetation restoration. When the soil water resources in the range of the maximum infiltration depth are equal to soil water resources use limit by plants, the plant water relation enters the key period of plant water relation regulation. If existing plant density is more than the soil water vegetation carrying capacity in the key period of plant water relation regulation, the plant water relation has to be regulated on the soil water vegetation carrying capacity to get maximal yield and service and realize high-quality sustainable management of forest vegetation in a water shortage area.

Seed priming with ascorbic acid improves response of Medicago polymorpha L. seedlings to osmotic stress induced by NaCl and PEG solutions

This study assessed to which extent seed priming with ascorbic acid (0.2 mM) may improve Medicago polymorpha L. performance under water shortage induced by irrigation with either 50 mM NaCl or 100 g/L polyethylene glycol (PEG). Parameters related to plant morphology, CO2/H2O leaf gas exchanges, osmotic adjustment, pigment content, and proline accumulation were specifically determined. Both NaCl and PEG solutions induced osmotic stress and reduced plant biomass (−30% and −40%, respectively), number of leaves and ramifications, stem length, net CO2 assimilation (−31% and 63%, respectively), and leaf water content. However, both treatments and especially PEG led to increased root/shoot ratios and leaf proline content. Interestingly, seed priming using ascorbic acid improved CO2/H2O gas exchange and plant biomass production (+66%, +100%, and +92% in control, NaCl-, and PEG-treated plants, respectively). It also improved the water relations as reflected by the decrease of leaf osmotic potential and higher leaf proline accumulation (+67% and +120% in PEG- and NaCl-treated plants, respectively) and water content (especially under PEG treatment). Besides, seed priming with ascorbic acid increased leaf carotenoid and chlorophyll contents (+65 and +45%, respectively, for chlorophyll a and chlorophyll b), thereby contributing to the better photosynthetic activity, and hence plant performance under salinity. We conclude that seed priming with ascorbic acid is an easy, cost-effective and promising approach to mitigate the impact of osmotic stresses like drought and salinity, by especially improving plant water relations and photosynthetic activity.

Ameliorating Drought Effects in Wheat Using an Exclusive or Co-Applied Rhizobacteria and ZnO Nanoparticles.

Drought is a major abiotic factor and affects cereal-based staple food production and reliability in developing countries such as Pakistan. To ensure a sustainable and consistent food supply, holistic production plans involving the integration of several drought mitigation approaches are required. Using a randomized complete block design strategy, we examined the drought-ameliorating characteristics of plant growth-promoting rhizobacteria (PGPR) and nanoparticles (NPs) exclusively or as a combined application (T4) through three stages (D1, D2, and D3) of wheat growth (T1, control). Our field research revealed that Azospirillum brasilense alone (T2) and zinc oxide NPs (T3) improved wheat plant water relations, chlorophyll, proline, phenolics and grain quality, yield, and their allied traits over the stressed treatments. Specifically, the best outcome was observed in the combined treatment of PGPR and ZnO NPs (T4). Interestingly, the combined treatment delivered effective drought mitigation through enhanced levels of antioxidants (15% APX, 27% POD, 35% CAT, 38% PPO and 44% SOD) over controls at the grain-filling stage (GFS, D3 × T1). The 40% improvements were recorded under the combined treatment at GFS over their respective controls. Their combined usage (PGPR and ZnO NPs) was concluded as an effective strategy for building wheat resilience under drought, especially in arid and semi-arid localities.

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

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