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Abstract Background Globally, salinity poses a threat to crop productivity by hindering plant growth and development via osmotic stress and ionic cytotoxicity. Plant extracts have lately been employed as exogenous adjuvants to improve endogenous plant defense mechanisms when grown under various environmental stresses, such as salinity. This study investigated the potential of melatonin (Mt; 0, 50, and 100 mM) as an antioxidant and licorice root extract (LRE; 0.0 and 3%) as an organic biostimulant applied sequentially as a foliar spray on faba bean (Vicia faba L.) grown in cadmium (Cd)-contaminated saline soil conditions [Cd = 4.71 (mg kg− 1 soil) and ECe = 7.84 (dS m− 1)]. Plants not receive any treatment and sprayed with H2O were considered controls. The experimental treatments were laid out in strip plot in a randomized complete block design replicated thrice, where the LRE and Mt were considered as vertical and horizontal strips, respectively. Growth characteristics, photosynthetic pigments, nutrient uptake, physiology and metabolic responses, anatomical features, and yield were assessed. Results Cadmium (Cd) and salinity-induced stress significantly altered leaf integrity, photosynthetic efficiency, total soluble sugars (TSS), free proline (FPro), total phenolic, DPPH, and total soluble proteins (TSP), non-enzymatic and enzymatic antioxidants, growth characteristics and yield-related traits. However, the application of LRE + Mt considerably improved these negative effects, with higher improvements were observed due to application of LRE + Mt100. Application of LRE + Mt significantly reduced hydrogen peroxide (H2O2) accumulation, lipid peroxidation and Cd content in leaves and seeds, all of which had increased due to Cd stress. Application of LRE + Mt significantly mitigated the Cd-induced oxidative damage by increasing the activity of reactive oxygen species (ROS) scavenging enzymes such as superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase, in parallel with enhanced ascorbate and reducing glutathione content. Exogenous application of LRE + Mt significantly increased osmolyte content, including FPro, TSS, and total phenols and mitigated Cd-induced reduction to considerable levels. Conclusions Our findings showed that LRE + Mt increased V. faba plants’ morphological, physiological, and biochemical properties, reducing Cd stress toxicity, and promoting sustainable agricultural practices. Clinical trial number Not applicable.

Abstract Background The combination of compost and biochar (CB) plays an important role in soil restoration and mitigation strategies against drought stress in plants. In the current study, the impact of CB was determined on the characteristics of saline calcareous soil and the productivity of fenugreek (Trigonella foenum-graecum L.) plants. The field trials examined CB rates (CB0, CB10 and CB20 corresponding to 0, 10, and 20 t ha‒1, respectively) under deficit irrigation [DI0%, DI20%, and DI40% receiving 100, 80, and 60% crop evapotranspiration (ETc), respectively] conditions on growth, seed yield (SY), quality, and water productivity (WP) of fenugreek grown in saline calcareous soils. Results In general, DI negatively affected the morpho-physio-biochemical responses in plants cultivated in saline calcareous soils. However, amendments of CB10 or CB20 improved soil structure under DI conditions. This was evidenced by the decreased pH, electrical conductivity of soil extract (ECe), and bulk density but increased organic matter, macronutrient (N, P, and K) availability, water retention, and total porosity; thus, maintaining better water and nutritional status. These soil modifications improved chlorophyll, tissue water contents, cell membrane stability, photosystem II photochemical efficiency, photosynthetic performance, and nutritional homeostasis of drought-stressed plants. This was also supported by increased osmolytes, non-enzymatic, and enzymatic activities under DI conditions. Regardless of DI regimes, SY was significantly (P ≤ 0.05) improved by 40.0 and 102.5% when plants were treated with CB10 and CB20, respectively, as similarly observed for seed alkaloids (87.0, and 39.1%), trigonelline content (43.8, and 16.7%) and WP (40.9, and 104.5%) over unamended control plants. Conclusions Overall, the application of organic amendments of CB can be a promising sustainable solution for improving saline calcareous soil properties, mitigating the negative effects of DI stress, and enhancing crop productivity in arid and semi-arid agro-climates.

Abstract The impact of bio-organic amendments on crop production is poorly understood in saline calcareous soils. The aim in the present study was to determine the effects of the application of organic manure along with lactic acid bacteria (LAB) on soil quality, and morpho-physio-biochemical responses, seed yield (SY) and essential oil yield (EOY) of fennel plants (Foeniculum vulgare Mill.) grown in saline calcareous soils. Eight treatments of farmyard manure (FM) or poultry manure (PM) individually or combined with Lactobacillus plantarum (Lp) and/or Lactococcus lactis (Ll) were applied to saline calcareous soil in two growing seasons. Either FM or PM combined with LAB had beneficial effects on lowering ECe, pH and bulk density and increasing total porosity, organic matter, and water and nutrient retention capacities in addition to total bacterial population in the soil. Growth, nutrient uptake, SY and EOY of plants were also enhanced when fennel seeds were inoculated with Lp and/or Ll and the soil was amended with any of the organic manures under unfavorable conditions. Compared to control (no bio-organic amendments), FM + Lp + Lt or PM + Lp + Lt treatment signficantlly (P ≤ 0.05) increased plant height by 86.2 or 65.0%, total chlorophyll by 73 or 50%, proline by 35 or 45%, glutathione by 100 or 138%, SY by 625 or 463% and EOY by 300 or 335%, respectively, in fennel plants. Co-application of the naturally occurring microorganisms (i.e., LAB) and organically-derived, nutrient-rich fertilizer (i.e., FM or PM) is recommended to improve yield of fennel plants in saline calcareous soils.

Purpose The effect of a novel organo-mineral fertilizer (OMF) compost, as a partial alternative to mineral fertilizers, on soil characteristics, growth, physio-biochemical attributes, Cd2? and NO3 - concentrations, and yields of Phaseolus vulgaris L. plants grown under salt stress was investigated. Methods Six organic and mineral materials were well mixed with water and composted in a polyvinyl house in a concrete trench of size 4 9 5 9 2m (W 9 L 9 D), respectively. The moisture content was maintained at 50â60% throughout the active composting period by frequent checking. The mixture was turned at 7-day intervals for about 2 months to maintain porosity. This OMF compost was applied for the tested saline soil at 10, 20 and 30 ton ha-1 while reducing the recommended NPK to 50%. In addition,100% NPK was applied as a control to achieve the purpose of this study. Growth characteristics, quantitative and qualitative yield, Cd2? and NO3 - concentrations, and physio-biochemical attributes in common bean plants were assessed. Results Addition of OMF compost improved the soil chemical and physical properties. Application of OMF compost at a rate of 20 ton h-1 , as an alternative to 50% of the recommended dose of mineral-NPK fertilizers, significantly decreased the concentrations of Cd2? and NO3 - in plant leaves, pods and seeds, showing the same growth characteristics, and pod and seed yields compared to the control (100% of mineral-NPK fertilizers). This treatment also improved all determined physio-biochemical attributes and tested soil characteristics compared to the control. Conclusion The benefit of this OMF compost, as a partial alternative to chemical fertilizers, demonstrated the validity and possibility of sustainable agronomic performance of common bean using locally available recycled organic materials for manufacturing the studied OMF.

The application of effective microorganisms (EMs) and/or nitrogen (N) have a stimulating effect on plants against abiotic stress conditions. The aim of the present study was to determine the impact of the co-application of EMs and N on growth, physio-biochemical attributes, anatomical structures, nutrients acquisition, capsaicin, protein, and osmoprotectant contents, as well as the antioxidative defense system of hot pepper (Capsicum annum L.) plants. In the field trials, EMs were not applied (EMs-) or applied (EMs+) along with three N rates of 120, 150, and 180 kg unit N ha-1 (designated as N120, N150, and N180, respectively) to hot pepper plants grown in saline soils (9.6 dS m-1). The application of EMs and/or high N levels attenuated the salt-induced damages to hot pepper growth and yield. The application of EMs+ with either N150 or N180 increased the number, average weight and yield of fruits by 14.4 or 17.0%, 20.8 or 20.8% and 28.4 or 27.5%, respectively, compared to hot pepper plants treated with the recommended dose (EMs- × N150). When EMs+ was individually applied or combined with either N150 or N180, increased accumulation of capsaicin were observed by 16.7 or 20.8%, protein by 12.5 or 16.7%, proline by 19.0 or 14.3%, and total soluble sugars by 3.7 or 7.4%, respectively, in comparison with those treated with the integrative EMs- × N150. In addition, the non-enzymatic contents (ascorbate, and glutathione) and enzymatic activities (catalase, superoxide dismutase, and glutathione reductase) of the antioxidant defense systems significantly increased in hot pepper plants treated with EMs+ alone or combined with N150 or N180 under salt stress conditions. Higher accumulation of nutrients (N, P, K+, and Ca2+) along with reduced Na+ acquisition was also evidenced in response to EMs+ or/and high N levels. Most anatomical features of stems and leaves recovered in hot pepper plants grown in saline soils and supplied with EMs+ and N. The application of EMs and N is undoubtedly opening new sustainable approaches toward enhancing abiotic stress tolerance in crops (e.g. hot pepper).

Calcareous soil had sufficient phosphorus and potassium (PK) in different forms due to the high contents of PK-bearing minerals; however, the available PK state was reduced due to its PK-fixation capacity. Compost, coupled with high PK solubilization capacity microbes, is a sustainable solution for bioorganic fertilization of plants grown in calcareous soil. A 2-year field experiment was conducted to investigate the effect of compost (20 t ha−1) with Aspergillus niger through soil drenching (C-AN) along with partial substitution of PK fertilization on quinoa performance in normal and calcareous soils. Treatments included PK100% (72 kg P2O5 ha−1 + 60 kg K2O ha−1 as conventional rate), PK100%+C-AN, PK75%+C-AN, PK50%+C-AN, PK25%+C-AN, and only C-AN in normal and calcareous soils. Results showed that C-AN and reduced PK fertilization (up to 75 or 50%) increased photosynthetic pigments and promoted nutrient acquisition in quinoa grown in calcareous soil. Reduced PK fertilization to 75 or 50% plus C-AN in calcareous soil increased osmoprotectants, nonenzymatic antioxidants, and DPPH scavenging activity of quinoa’s leaves compared to the PK0%+C-AN treatment. The integrative application of high PK levels and C-AN enhanced the quinoa’s seed nutritional quality (i.e., lipids, carbohydrates, mineral contents, total phenolics, total flavonoids, half maximal inhibitory concentration, and antiradical power) in calcareous soil. At reduced PK fertilization (up to 75 or 50%), application of compost with Aspergillus niger through soil drenching increased plant dry weight by 38.7 or 53.2%, hectoliter weight by 3.0 or 2.4%, seed yield by 49.1 or 39.5%, and biological yield by 43.4 or 33.6%, respectively, compared to PK0%+C-AN in calcareous soil. The highest P-solubilizing microorganism’s population was found at PK0%+C-AN in calcareous soil, while the highest Azotobacter sp. population was observed under high PK levels + C-AN in normal soil. Our study recommends that compost with Aspergillus niger as a bioorganic fertilization treatment can partially substitute PK fertilization and boost quinoa’s tolerance to salt calcareous-affected soil.

Salinity is a major threat to the sustainability of agricultural production systems. Salt stress has unfavorable implications on various plant physio-morphological and biochemical reactions, causing osmotic and ionic stress. Exogenously applied folic acid (FA) may at least provide one mechanism to evade the injurious stress effects of saline irrigation water on Plectranthus amboinicus. In this regard, two pot trials were performed during the 2018–2019 and 2019–2020 seasons in an open greenhouse of an experimental farm (29°17'N; 30°53'E) in Fayoum, Egypt. We tested four levels of saline irrigation water (SW): 34, 68, and 102 mM NaCl, plus tap water as the control = 0), combined with FA at three concentrations (25 and 50 μM, plus spray with distilled water as the control = 0). The growth parameters, biochemistry, physiology, elemental leaf status, essential oil content, and anatomical responses were assessed. Salt markedly reduced photosynthetic productivity [Fv/Fm and performance index (PI)], total chlorophyll [soil plant analysis development (SPAD)], and leaf osmoprotectant compounds, i.e., total soluble sugars (TSS), free amino acids, proline, and total phenolics, thus hampering P. amboinicus growth and essential oil yield. However, the addition of FA as a foliar spray to P. amboinicus irrigated with saline water induced increases in Fv/Fm, SPAD, and PI. These were linked with enriched stem anatomical structures, leaf osmoprotectant compounds, and enhanced leaf enzymatic activity, e.g., superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase, glutathione, ascorbic acid, and antioxidant content. Under salt stress, supplementation of 25 and 50 μM FA increased the growth and production of essential oil by 27.8 and 55.6%, respectively, compared with no applied FA. The highest growth characteristics and elemental leaf contents were obtained when P. amboinicus was irrigated with 0 mM saline water and treated foliarly with 50 μM of FA compared with non-treated plants. Overall, these data showed that foliar spraying with FA reduces the impact of salt stress on P. amboinicus irrigated with saline water.

The application of bio- and nanofertilizers are undoubtedly opening new sustainable approaches toward enhancing abiotic stress tolerance in crops. In this study, we evaluated the application of effective microorganisms (EMs) of five groups belonging to photosynthetic bacteria, lactic acid bacteria, yeast, actinobacteria, and fermenting fungi combined with magnesium oxide (MgO) nanoparticles (MgO-NP) on the growth and productivity of sweet potato plants grown in salt-affected soils. In two field experiments carried out in 2020 and 2021, we tested the impacts of EMs using two treatments (with vs. without EMs as soil drench) coupled with three foliar applications of MgO-NP (0, 50, and 100 μg ml–1 of MgO, representing MgO-NP0, MgO-NP50, and MgO-NP100, respectively). In our efforts to investigate the EMs:MgO-NP effects, the performance (growth and yield), nutrient acquisition, and physio-biochemical attributes of sweet potatoes grown in salt-affected soil (7.56 dS m–1) were assessed. Our results revealed that salinity stress significantly reduced the growth parameters, yield traits, photosynthetic pigment content (chlorophylls a and b, and carotenoids), cell membrane stability, relative water content, and nutrient acquisition of sweet potatoes. However, the EMs+ and/or MgO-NP-treated plants showed high tolerance to salt stress, specifically with a relatively superior increase when any of the biostimulants were combined. The application of EMs and/or MgO-NP improved osmotic stress tolerance by increasing the relative water content and membrane integrity. These positive responses owed to increase the osmolytes level (proline, free amino acids, and soluble sugars) and antioxidative compounds (non-enzymatic concentration, enzymatic activities, phenolic acid, and carotenoids). We also noticed that soil salinity significantly increased the Na+ content, whereas EMS+ and/or MgO-NP-treated plants exhibited lower Na+ concentration and increased K+ concentration and K+/Na+ ratio. These improvements contributed to increasing the photosynthetic pigments, growth, and yield under salinity stress. The integrative application of EMs and MgO-NP showed higher efficacy bypassing all single treatments. Our findings indicated the potential of coapplying EMs and MgO-NP for future use in attenuating salt-induced damage beneficially promoting crop performance.