Mitigation Strategies and Tolerance of Plants to Abiotic Stresses

Dear Colleagues,

Semi-arid and arid areas around the world are subject to a qualitative and quantitative scarcity of water resources. Thus, both scarcity (water deficit) and the occurrence of water sources with high salt concentrations stand out as limiting factors for agricultural production. Thus, there is an urgent need to establish strategies that mitigate abiotic stresses aimed at facilitating the sustainability of crops and meeting growing needs for food production. This Special Issue on Mitigation Strategies and Plant Tolerance to Abiotic Stresses presents original research results on the effects of abiotic stresses, tolerance mechanisms, crop tolerance associated with mitigation strategies, and biomolecular mechanisms. Submitted manuscripts must not be previously published or under evaluation for publication in another journal.

Prof. Dr. Geovani Soares de Lima
Prof. Dr. Lauriane Almeida dos Anjos Soares
Prof. Dr. Francisco Vanies Da Silva Sá
Guest Editor

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• salt and water stress
• tolerance mechanisms
• oxidative stress
• hydroponic cultivation
• hydroponic cultivation
• fertilizing
• eliciting substances

Title: Application Methods and Concentrations of Ascorbic Acid as a Saline Stress Attenuator in Passion Fruit Cultivation
Authors: Edmilson Júnio Medeiros Caetano 1, André Alisson Rodrigues da Silva 1, Geovani Soares de Lima 1,*, Carlos Alberto Vieira de Azevedo 1, Luana Lucas de Sá Almeida Veloso 1, Thiago Filipe de Lim
Affiliation: Academic Unit of Agricultural Engineering; Federal University of Campina Grande, Campina Grande 58430-380, PB, Brazil
Abstract: Salinity is one of the abiotic stresses that most limits the development of irrigated fruit growing in semi-arid regions of Brazil. In this sense, the search for strategies that minimize the effects of saline stress is extremely important. Among these strategies, the use of elicitor substances such as ascorbic acid stands out; however, the beneficial effects of ascorbic acid may depend on the concentration and application method used. In this context, the objective of this study was to evaluate the effects of ascorbic acid concentrations and application methods on the levels of photosynthetic pigments, gas exchange and water relations in sour passion fruit irrigated with brackish water. The treatments were distributed in a randomized block design, in a 3 × 3 × 2 fac-torial scheme, corresponding to three application methods (soaking, spraying and soaking + spraying), three concentrations of ascorbic acid (0, 0.8, and 1.6 mM) and two levels of electrical conductivity of irrigation water (0.8 and 3.8 dS m-1) with three replicates and one plant per plot. The foliar spray of ascorbic acid at a concentration of 0.8 mM mitigated the effects of saline stress on the relative content of leaf water, photosynthetic pigments and gas exchange in sour passion fruit. However, the best results were obtained in plants irrigated with an ECw of 0.8 dS m-1

Title: Exogenous Sodium Nitroprusside Treatment Affects the Redox System of Wheat Roots Differentially Regulating the Activity of Antioxidant Enzymes Under Short-Time Osmotic Stress
Authors: Alsu R. Lubyanova*; Chulpan R. Allagulova
Affiliation: Institute of Biochemistry and Genetics - Subdivision of the Ufa Federal Research Centre of the Russian Academy of Sciences, Russia
Abstract: The understanding the mechanisms of nitric oxide (NO)-induced plant`s adaptation to environmental changes is an important step for receiving the productive and tolerant crops in the future. 12% polyethylene glycol 6000 (PEG) supplementation during 0.5-24 h caused in wheat roots transient superoxide (O2•-) and hydrogen peroxide (H2O2) accumulation, the increase of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) activities, level of malondialdehyde (MDA), and electrolyte leakage (EL) as compared to control. 2 × 10-4 M sodium nitroprusside (SNP/+NO, NO donor) pretreatment for 24 h decreased the O2•-, H2O2 generation, MDA accumulation, and EL of wheat roots subjected to osmotic stress for 0.5-24 h as compared to SNP-untreated stressed plants. (SNP/+NO) pretreatment differently regulated the activity of antioxidant enzymes at the initial phase of osmotic stress, so NO donor reduced SOD, POD, CAT activities during 4 h of PEG influence, and stimulated their activity under 24 h of wheat exposure to osmotic stress as compared to SNP-untreated stressed plants. Osmotic stress triggered in 57-fold excretion of proline by wheat roots into the growth medium. (SNP/+NO) pretreatment additionally increased proline accumulation in wheat nutrient solution during 12% PEG application as compared to (SNP/+NO) pretreatment alone.

Title: Physiological and proteomic changes of Helianthus annus L. in response to elevated CO2 and biofertilization with Rizophagus irregularis
Authors: Bellido, E.; Agüera E.
Affiliation: Department of Botany, Ecology and Plant Physiology, Faculty of Science, University of Córdoba, 14071 Córdoba, Spain
Abstract: In this work we are going to examine the effect of increasing atmospheric CO2 on primary sunflower leaves of plants biofertilized with Rizophagus irregularis. To do this, physiological markers commonly used to control leaf development will be examined. In addition, a proteomic approach will be used to identify differentially expressed proteins between biofertilized plants grown at high CO2 versus biofertilized plants grown. in environmental CO2, as well as between non-biofertilized plants grown at high CO2 and biofertilized plants grown at high CO2. The molecular differences detected in the primary leaf could provide information about the greater tolerance of Helianthus annuus L. to the stress conditions that are known to be caused by high CO2 in this plant. Through these results, relevant information can be provided to understand the adaptation mechanism of this plant with a view to future scenarios. where the concentration of CO2 in the atmosphere will be increased.

Title: Oxyfertigation in adult citrus trees based on the application of hydrogen peroxide in irrigation water. Physiological and agronomic response
Authors: Juan M. Robles 1*, Josefa M. Navarro 1, Pablo Botía 1 and Juan G. Pérez 1,2
Affiliation: 1 Equipo de Riego y Fisiología del Estrés, Instituto Murciano de Investigación y Desarrollo Agrario y Medioambiental (IMIDA), 30150 La Alberca, Region of Murcia, Spain; [email protected] (J.M.N.); [email protected] (P.B.); [email protected] (J.G.P.-P.) 2 Centro Para el Desarrollo de la Agricultura Sostenible, Instituto Valenciano de Investigaciones Agrarias (IVIA), 46113 Moncada, Valencia Province, Spain
Abstract: The use of oxyfertigation in citrus trees as a palliative technique to increase the oxygen content in the root zone, under conditions of no soil tillage, is scarcely studied. Therefore, the objec-tive of the work was to study the physiological and agronomic response of the application of chem-ical oxyfertigation, based on the application of hydrogen peroxide (H2O2) in irrigation water as a source of oxygen at the root level to increase water use efficiency (WUE). The experiment took place during four seasons (2019-2022) on adult 'Ortanique' hybrid mandarin trees located in an orchard in Torre Pacheco (Murcia). A 'Control' treatment (0 ppm of H2O2) and another identified as 'OXI' (50-100 ppm of H2O2 throughout the cultivation cycle) were established. The 'OXI' treatment signif-icantly increased the level of dissolved oxygen in the irrigation water, as well as the diffusion rate of oxygen in the soil. This was reflected in a significant improvement in the gas exchange parameters in the plant during the cultivation cycle. However, production and WUE did not show significant differences, although a trend of increasing cumulative production of 13% was noted, due to a greater number of fruits harvested (around 18%). Therefore, the possible agronomic improvements from the use of oxyfertigation in citrus trees would tend to occur in the long term.

Title: Comparison of Growth and Physiological Effects of Soil Moisture Regime on Plantago maritima Plants from Geographically Isolated Sites on the Eastern Coast of the Baltic Sea
Authors: Katrīna Anna Ozoliņa; Astra Jēkabsone; Una Andersone-Ozola; Gederts Ievinsh
Affiliation: Department of Plant Physiology, Faculty of Biology, University of Latvia, 1 Jelgavas Str., LV–1004 Riga, Latvia
Abstract: The aim of the present study was to evaluate the morphological and physiological responses of P. maritima plants from five geographically isolated sites growing in habitats with different conditions to different substrate moisture levels in controlled conditions. Plants were produced from seed and cultivated in a greenhouse at four relatively constant soil moisture regimes: at 25, 50, 75% soil water content as well as in soil flooded 3 cm above the surface (80% F). The two morphological traits that varied most strikingly among P. maritima accessions were the number of flower stalks and the number of leaves. Only plants from two accessions uniformly produced generative structures, and allocation to flowering was suppressed by both low moisture and flooding. Optimum shoot biomass accumulation for all accessions was at 50 and 75% soil moisture. Performance Index Total was the most sensitive among the measured photosynthesis-related parameters and it tended to decrease with an increase in soil water content for all P. maritima accessions. The initial hypothesis that plants from relatively dry habitats will have higher tolerance against low soil water level, but plants from relatively wet habitats will have higher tolerance against waterlogged or flooded soil was not approved. The existence of three ecotypes of P. maritima within the five accessions from geographically isolated subpopulations on the eastern coast of the Baltic Sea at the level of morphological responses to soil water content can be proposed. P. maritima plants can be characterized as extremely tolerant to soil waterlogging and highly tolerant to soil flooding and low soil water content.

Title: Recovery effect of secondary paper sludge on physiological traits of Lactuca sativa L. under heavy metal stress
Authors: Yurkevich M., Kurbatov A.A., Ikkonen E*
Affiliation: Institute of Biology of the Karelian Research Centre, Russian Academy of Sciences, Petrozavodsk 185910, Russia
Abstract: To eliminate the negative effect of soil contamination with heavy metal on plant growth and crop yield, different methods and techniques are under discussion and study. In this study we aimed to evaluate the effect of secondary pulp and paper mill sludge application to soil on the response of the main physiological processes such as growth, photosynthesis, respiration and water metabolism of lettuce (Lactuca sativa L.) plants to soil contamination with Pb. For the pot experiment, Pb was added in the loamy Retisol soil with the rate of 0, 50, and 250 mg Pb(NO3)2 per kg of the soil, and secondary sludge was added with each watering plants with a 0, 20 or 40% sludge solution. The Pb-mediated change in plant biomass allocation, decrease in the photosynthetic rate, as well as increase in leaf respiration rate and in degree of light inhibition of respiration were closely associated with increases in both root and shoot Pb content. For Pb-free soil condition, secondary sludge application contributed to redistribution of plant biomass towards greater accumulation in the shoots than in the roots. Although stomatal opening was not affected by either lead or waste, addition of waste increased photosynthetic CO2 assimilation regardless of soil Pb content, which was associated with an increase in electron transport rate and carboxylase activity of Rubisco. Soil contamination with Pb significantly increased a ratio of respiration to photosynthesis, reflecting a shift in the carbon balance toward carbon losses by plants but sludge application modified the coupling between the processes with a decrease in the proportion of respiratory carbon losses. Sludge-mediated recovery of the physiological processes of L. sativa reflected an increase in plant tolerance to soil contamination with heavy metal, the formation of which is associated with plant adjustments initiated by secondary sludge application.

Title: Orchard climate control as a way to improve the kiwifruit tolerance to climate change and prevent decline syndrome onset
Authors: Claudio Mandalà1, Luca Nari2, Stefano Monaco1, Francesco Palazzi1, Chiara Morone3, Grazia Federica Bencresciuto1, and Laura Bardi1
Affiliation: 1 Research Centre for Engineering and Agro-Food Processing, CREA Council for Agricultural Research and Economics, Turin, Italy 2 AGRION, The Foundation for Research, Innovation and Technological Development of Piedmont Agriculture, Manta, Italy 3 Phytosanitary and Scientific-technical services Department, Agricultural and Food Directorate, Piedmont Region, Turin, Italy
Abstract: Kiwifruit cultivation is severely affected in several Mediterranean areas by a syndrome called "kiwifruit decline syndrome". The symptoms appear in the canopy with growth arrest and wilt that rapidly progress to desiccation; roots show growth arrest, absence of fine feeder roots, brown soft-rotting areas and cortical detachment from the central cylinder. A specific cause has not been identified, and a multifactor origin is generally recognised for this syndrome. A correlation of symptoms onset with hydraulic conductance impairment caused by climate stress was detected, in particular by vapour pressure deficit and high temperature; then, it can be assumed that climate change increases the weakness and sensibility of kiwifruit to other biotic and abiotic stress factors, inducing the occurrence of this syndrome. In this work a climate control system was tested for three years in an experimental orchard, using shading nets and over-tree micro-sprinkler irrigation, aimed at protecting leaves from overheating and locally decreasing vapour pressure deficit stress. Plants were monitored for physiological and morphological parameters (leaf gas exchanges, leaf temperature, stem water potential, stem growth, root starch content, root xylem vessels diameter, density and vulnerability to cavitation). Narrow diameters of xylem vessels were observed in all plants, including those of the control plot, as a sign of a general long-term adaptation strategy to rising vapour pression deficit for lower vulnerability to cavitation. A positive effect of the orchard climate control system was detected: lower leaf temperature throughout the whole vegetative season, higher leaf water potential, higher stomatal conductance and photosynthetic activity were detected, in particular in afternoon and in autumn; moreover, the root starch content was higher in springtime. No decline syndrome symptoms were detected. These results indicates that a proper agronomic management can protect kiwifruit plants from climate stress, decreasing the risk of decline syndrome onset.