Soil science
Seyed Hamidehi Mousavi Dizkouhi; Mojtaba Barani Motlagh; Esmaeil Dordipour; Elham Malekzadeh; Fardin Sadeghzadeh; mahmmod ghasem nezhad
Abstract
Introduction
The olive tree (Olea europaea L.) is one of the most significant and ancient cultivated plants in the Mediterranean region, prized for its edible fruit and high-quality oil. However, the increasing scale of olive oil production has led to the accumulation of large quantities of solid waste, ...
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Introduction
The olive tree (Olea europaea L.) is one of the most significant and ancient cultivated plants in the Mediterranean region, prized for its edible fruit and high-quality oil. However, the increasing scale of olive oil production has led to the accumulation of large quantities of solid waste, particularly olive solid pomace (OSP), which poses considerable environmental challenges due to its high organic load and phytotoxic components. Sustainable management and valorization of this waste are crucial for reducing environmental risks and improving the circular economy in agricultural systems. This study aimed to evaluate the effects of compost and vermicompost derived from OSP, both in enriched and non-enriched forms, on the yield of olive fruit and the quality characteristics of the resulting olive oil. To this end, a field experiment was conducted during the 2018 growing season in a traditional olive orchard located in Rudbar, Gilan Province, Iran. The experiment was carried out using a randomized complete block design (RCBD) with 12 treatments and three replications on the ‘Arbequina’ cultivar, a well-known olive variety cultivated for its high oil content and quality.
Materials and Methods
Compost and vermicompost were first produced from olive solid pomace. After analyzing their basic physicochemical properties, several treatments were biologically enriched using plant growth-promoting rhizobacteria (PGPR), including Bacillus megaterium (phosphorus-solubilizing), Azotobacter chroococcum (nitrogen-fixing), and Thiobacillus thioparus (sulfur-oxidizing). Additional treatments were chemically enriched by incorporating 1 kg each of urea (as a nitrogen source), triple superphosphate (as a phosphorus source), and elemental sulfur at a rate of 1% by weight. The experimental treatments included: raw olive pomace, unenriched compost, chemically enriched compost, biologically enriched compost, unenriched vermicompost, chemically enriched vermicompost, biologically enriched vermicompost, a full NPK fertilizer treatment, a manure-only treatment (10 kg of animal manure), and a no-fertilizer control. All olive waste-based amendments were applied at 3% w/w. NPK fertilizers included urea (750 g in three split applications), triple superphosphate (250 g), and potassium sulfate (750 g). Micronutrients such as magnesium sulfate, manganese, iron, zinc, copper, boric acid, and elemental sulfur were applied based on soil test recommendations. Uniform horticultural practices, including surface drip irrigation, weed control, pest management, and other cultural operations, were applied across all plots. Post-treatment, soil samples were collected at depths of 0–30, 30–60, and 60–90 cm to measure pH, EC, organic carbon, and available phosphorus. Foliar sprays were prepared with 1,000 ml solutions of urea and potassium sulfate (10 g/L), zinc sulfate (3 g/L), and boric acid (5 g/L) and applied twice at sunset using a handheld sprayer. Fruit yield, oil content, and selected oil quality parameters were then assessed.
Results and Discussion
Application of biologically enriched vermicompost significantly improved olive yield and oil quality. Trees receiving this treatment produced 50.33 kg of fruit per tree—an increase of 93.58% compared to the control. Similarly, the highest oil yield (11.14 kg per tree) was recorded in the biologically enriched vermicompost treatment. The lowest peroxide value (1.06 meq O₂/kg oil) was also observed in this treatment, representing an 88.27% reduction compared to the control. Organic fertilizers positively influenced the oil percentage of the fruit, with biologically enriched compost yielding the highest oil content (57.77%), which was 132.19% higher than the control. The extinction coefficients K270 and K232, indicators of oil oxidation, were reduced by 96.24% and 78.53%, respectively, in the biologically enriched vermicompost treatment. Furthermore, this treatment resulted in the lowest free fatty acid content—94.66% lower than the control. Leaf phosphorus content was also significantly enhanced, reaching 0.33% in the biological vermicompost treatment, a 230% increase over the control. These findings underscore the beneficial role of organic fertilizers, particularly biologically enriched vermicompost, in improving soil fertility, nutrient availability, and plant performance. The high phosphorus content in the compost and vermicompost, combined with microbial activity, played a pivotal role in enhancing both yield and oil quality. The application of PGPRs proved particularly effective, as they not only facilitated nutrient cycling but also contributed to improved physiological responses in olive trees.
Conclusions
Overall, the results suggest that olive trees fertilized with biologically enriched organic amendments derived from olive pomace benefit from improved oil quality and fruit yield. The presence of adequate phosphorus and beneficial bacteria played a pivotal role in enhancing plant nutrition and oil characteristics. Therefore, the use of PGPR in the enrichment of composted organic materials can be an effective and sustainable strategy to improve the productivity and quality of olive oil. Among the treatments, biologically enriched vermicompost emerged as the most effective and is recommended for further field application. Future research should explore other organic amendments and their long-term effects on olive orchards.
Elham Malekzadeh; Jafar Majidi; Nasser Aliasgharzad; Jalal Abdolalizadeh
Abstract
Introduction: Glomalin is known as a specific fungal glycoprotein belonging to the order Glomerales in phylum Glomeromycota and has been introduced as a heat shock protein. We hypothesised that increasing the level of Pb would lead to increase in glomalin production. Glomalin is usually determined by ...
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Introduction: Glomalin is known as a specific fungal glycoprotein belonging to the order Glomerales in phylum Glomeromycota and has been introduced as a heat shock protein. We hypothesised that increasing the level of Pb would lead to increase in glomalin production. Glomalin is usually determined by two methods, the Bradford protein dye-binding assay and the enzyme-linked immunosorbent assay (ELISA). Since many laboratories are not equipped to carry out the ELISA assay, many studies have measured glomalin-related soil protein using the Bradford colorimetric total protein assay. While, the ELISA method specifically measures glomalin by using monoclonal antibody MAb32B11.
Materials and Methods: The pot experiment was conducted in the sterile free-glomalin sand with Trifolium repens L. mycorrhized by Rhizophagus irregularis fungus and treated with the Pb levels of 0, 150, 300 and 450 µM. Thus, in vitro experiment was performed in two-compartments plates containing of the transformed carrot roots (Daucus carota L.) mycorrhized with the same fungus in root compartment and hyphal compartment treated with the Pb levels of 0, 0.01, 0.1 and 1 mM as Pb(NO3)2. For glomalin extraction, hyphal or root samples were autoclaved at 121 ⁰C with 50 mM sodium citrate buffer for 60 min in three cycles. Protein concentrations in the extracted samples were determined using a modified Bradford protein assay. Also, glomalin content in the samples were determined by indirect ELISA using monoclonal antibody MAb32B11. The percentages of the total root length were colonised by mycorrhizal fungi in pot culture and both hyphal and spore densities in the metal-containing hyphal compartment were determined.
Results and Discussion: In the in vitro culture the percentage of total hyphae and spore frequency decreased, while Bradford reactive total hyphal protein (BRHP) and Immunoreactive hyphal protein (IRHP) in hyphal compartment increased as the concentrations of Pb increased. Also, there was positive and significant correlation between immunoreactive hyphal protein (IRHP) and Bradford reactive total hyphal protein (BRHP) in hyphal compartment of in vitro culture (r= 0.941**). In the pot culture, the percentage of the total mycorrhized root length in all the treatments increased compared to the unleaded control as the concentrations of Pb raised. In general, Bradford reactive total protein and Immunoreactive protein in both the hyphal and root compartments of pot culture increased with increasing the Pb levels. Also, there were positive and significant correlations between immunoreactive hyphal protein (IRHP) with Bradford reactive total hyphal protein (BRHP) (r= 0.845 **) and immunoreactive root protein (IRRP) with Bradford reactive total root protein (BRRP) (r= 0.706 **) in pot experiment. Some previously researches had reported correlation between ELISA with Bradford contents, whether, Bradford and ELISA values were nearly the same, this means that the extraction process mostly separates glomalin. The results of non-mycorrhizal roots indicated that a small proportion of root protein is cross-reactive with the MAb32B11 antibody. There are some evidences that MAb32B11 is slightly cross-reactive with plant compounds, non-AMF species, and non-target proteins present in large concentration, such as BSA. Additionally, we found the increasing of BRRP contents of AMF-colonized root compared to the non-mycorhizal roots. This may be as a result of uptake and storage of arginine within AMF intraradical hyphae. Considering IRHP to BRHP ratio indicates that immunoreactivity percentage enhances by rising Pb levels. Immunoreactivity indicates a molecular configuration similar to the configuration of glomalin on hyphae. Our findings are in agreement with previous observations confirming that the toxicity-induced stress by metals may be enhancing glomalin production by AMF. The sequence of the glomalin gene revealed that is likely a 60-KDa heat-shock protein (Hsp) homolog. Glomalin relation with the heat shock proteins clarifies how stress is imposed by heavy metals may rapidly increase glomalin production by AMF and its concentrations in polluted soils.
Conclusion: The high contents of glomalin along with the increasing of Pb concentrations may be explained by the overexpression of this protein. This suggests that under Pb-induced stress and the toxic effect of Pb, the fungus exerts a protective mechanism against toxicant. Therefore, glomalin as a heat shock protein can involve in the reduction of possible cytosolic damages and the transfiguration of proteins under Pb toxicity. We can conclude that glomalin may reduce toxic elements availability via their stabilization and decrease their toxicity risk to other microorganisms and plants in heavy metal polluted sites.
E. Malekzadeh; H.A. Alikhani; Gh.R. Savaghebi; M. Zarei
Abstract
Abstract
In this study, interaction between AMF (G. mosseae and Glomus spp., respectively indigenous and non-indigenous of HM-contaminated areas) with Cd-resistant PGPRs (Bacillus mycoides and Micrococcus roseus, indigenous of contaminated areas) on the growth, Cd and nutrient uptake of maize plant ...
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Abstract
In this study, interaction between AMF (G. mosseae and Glomus spp., respectively indigenous and non-indigenous of HM-contaminated areas) with Cd-resistant PGPRs (Bacillus mycoides and Micrococcus roseus, indigenous of contaminated areas) on the growth, Cd and nutrient uptake of maize plant (Zea mays L.) in Cd polluted soil were investigated. With increasing levels of Cd, shoot and root dry weights, shoot Fe and P contents decreased but root and shoot Cd content increased. Root colonization was varied at different levels of Cd and co-inoculation with PGPRs. G. mosseae treatment had greatest amount of shoot and root dry weight, Fe and P of shoot at high concentration of Cd. At the levels of 100 and 200 Cd, in only mycorrhizal treatments, plants colonized by Glomus spp. and G. mosseae had respectively high content of Cd roots. At both levels of Cd, shoot Cd content in co-inoculation of M. roseus and B. mycoides with G. mosseae increased and decreased respectively in comparison with single inoculation of G. mosseae. While, at the levels of 100 and 200 Cd, shoot Cd content in co-inoculation of PGPRs with Glomus spp. respectively increased and decreased/did not significant different compared to single inoculation of Glomus spp. Co-inoculation of G. mosseae and M. roseus, with maximum Cd-accumulated in plant, was the most effective treatment in Cd phytoremediation and stabilization.
Keywords: AM fungi, Plant growth promoting rhizobacteria, Phytoremediation, Cd and maize
