Akbar Karimi; Habib Khodaverdiloo; MirHasan Rasouli Sadaghiani
Abstract
Introduction: Recently, due to enhancement of industrialization, urbanization and disposal of wastes, fertilizers and pesticides the concentration of heavy metals (HMs)in agricultural soil has increased. Heavy metals are serious threat for environment due to their hazardous effects. Lead (Pb) is one ...
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Introduction: Recently, due to enhancement of industrialization, urbanization and disposal of wastes, fertilizers and pesticides the concentration of heavy metals (HMs)in agricultural soil has increased. Heavy metals are serious threat for environment due to their hazardous effects. Lead (Pb) is one of the toxic heavy metal that threats the health of plants, living organisms and human. Excessive Pb concentrations in agricultural soils result in decreasing the soil fertility and health which affects the plant growth and leads to decrease in plant growth. Plants simultaneously exposed to Pb suffer morphological, biochemical and physiological injury. Pb adversely affect plant absorption of essential elements, chlorophyll biosynthesis and shoot and root growth. Arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) are known to enhance nutrient uptake and improvement of plant growth and tolerance in heavy metal contaminated soils through different mechanisms including producing low molecular weight organic acids, siderophore, antibiotics and hormones. The objective of this study was to evaluate the effect of AMF and PGPR on yield, leaf relative water content (RWC), some biochemical properties and uptake of Pb, Fe and Zn by Hyoscyamus (Hyoscyamus niger L.) under soil Pb contamination.
Materials and Methods: This study was carried out in greenhouse condition as a factorial experiment based on a randomized complete block design with two factors including Pb concentration (in four levels) and microbial treatment (in three levels including arbuscular mycorrhizal fungi, plant growth-promoting rhizobacteria and control) and in three replications. Consequently, a soil was selected and spiked uniformly with concentrations of Pb (0, 250, 500 and 1000 mg Pb kg-1 soil). The contaminated soil was then sterilized and inoculated with the selected species of arbuscular mycorrhizal fungi (a mixture of Glomus species including G. intraradices, G. mosseae and G. fasciculatum) or plant growth-promoting rhizobacteria (a mixture of Pseudomonas species includeing P. putida, P. fluorescens, and P. aeruginosa). Seeds of Hyoscyamus niger L. plant were grown in pots containing the Pb spiked soil. At the end of growth period shoot length, dry weights of root and shoot, Fe, Zn and Pb concentration in shoot, and some biochemical and physiological properties of plant including relative water content (RWC) chlorophyll a, b and total chlorophyll, carotenoids, proline and soluble sugars, were measured.
Results and Discussion: Results indicated that with increasing soil Pb concentration, dry weights of root and shoot, shoot length, photosynthetic pigments contents (chlorophyll a, chlorophyll b, total chlorophyll and carotenoids), shoot Fe and Zn concentration decreased, while proline and soluble sugars contents and the shoot Pb concentration increased. With increasing of soil Pb concentration, relative water content decreased, however, this reduction in concentration of 1000 mg Pb kg-1 soil was not significant (P > 0.05) in compared with concentration of 1000 mg Pb kg-1 soil. Amounts of all measured properties in AMF and PGPR treatments were higher than that control treatment. The highest values of shoot weight and root weight, were observed in plants that inoculated with AMF. The lowest shoot weight was recorded in non-inoculated plants that were grown under 1000 mg Pb kg-1 soil concentration. In this study Arbuscular mycorrhizal fungi and plant growth-promoting rhizobacteria inoculation led to a significant increase (P≤0.05) in shoot length (12.9 -71.1%), shoot dry weight (11.5 – 81%), root dry weight (18.4 – 60.6%), chlorophyll (8.5 – 36.5%) and carotenoid (11.5 – 40.0%) pigments, proline (55 – 115.7%), soluble sugars (17.6 – 72.2%) and shoot Fe (9.5 – 57.2%) and Zn (25.0 – 165.5%) concentration in shoot at different levels of soil Pb. The highest and lowest amounts of shoot Fe, Zn and Pb concentration observed in AMF and control treatments respectively. Plant growth promoting rhizobacteria were more effective than arbuscular mycorrhizal fungi in shoot Fe, Zn and Pb concentration, while the mean of shoot length and shoot and root dry weight was higher in plants that inoculated with AMF compared to ones inoculated with PGPR. In general, there were not significant (P ≤ 0.05) differences in amounts of chlorophyll (chlorophyll a, b and chlorophyll a+b) and carotenoids pigments, proline and soluble sugars between AMF and PGPR treatments.
Conclusion: It could be concluded that microbial inoculation (mixture of AMF and PGPR species) with improvement of plant biochemical properties results in improved Hyoscyamus niger L. yield and increased tolerance to Pb toxicity. Thus, the use of microbial inoculation (mixture of AMF and PGPR species) inoculation might be suggested for enhancement of plant tolerance in Pb contaminated soils.
saeid hokmalipour; mehdi panahyankivi; manocher shiri janagard
Abstract
Introduction: The excessive uses of chemical fertilizers have generated several environmental problems. Some of these problems can be tackled by use of Biofertilizer, which are natural, beneficial and ecologically friendly. The Biofertilizers provide nutrients to the plants and maintain soil structure. ...
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Introduction: The excessive uses of chemical fertilizers have generated several environmental problems. Some of these problems can be tackled by use of Biofertilizer, which are natural, beneficial and ecologically friendly. The Biofertilizers provide nutrients to the plants and maintain soil structure. Biofertilizer is an alternative to mineral fertilizers for increasing soil productivity and plant growth in sustainable agriculture. Plant growth promoting rhizobacteria (PGPR) are a group of bacteria that actively colonize plant roots and increase plant growth and yield. There is a widespread distribution of PGPR that flourishes in different geographical habitats. These rhizobacteria significantly affect plant growth not only by increasing nutrient cycling, also by suppressing pathogens by producing antibiotics and siderophores or by bacterial and fungal antagonistic substances and/or by other plant hormones. Inoculation of plants with Azospirillum could result in significant changes in various growth parameters, such as increase in plant biomass, nutrient uptake, tissue N content, plant height, leaf size and root length of cereals. Thus, it has been shown that Azospirillum and Pseudomonas have the potential for agricultural exploitation and can be used as natural fertilizers. The divers array of bacteria including Pseudomonas, Azospirillum, Azotobacter, Bacillus, Klebsilla, Entrobacter and Serratia seem to promote plant growth. These bacteria are important components of the rhizosphere of many plants, and are known to colonize the rhizosphere of wheat, potato, maize, grasses, pea and cucumber. Strains of Pseudomonas putida and Pseudomonas fluorescens could increase root and shoot elongation in wheat. Azospirillum, Pseudomonas and Azotobacter strains could affect seed germination and seedling growth
Materials and Methods: To investigate yield, yield components and some qualitative and quantitative characteristics of safflower at different planting dates, a factorial experiment was conducted based on randomized completed block design with three replications in 2016 at the laboratory of Agricultural University of Payam Noor, Kosar (Kivi) branch. The first factor consists of three sowing dates (5 March, 20 April and 5 May) and the second factor involves the seeds inoculation with plant growth promoting rhizobacteria (no inoculation, seed inoculation with Azotobacter chorchorum strain 5 and Azosprilium lipoferum strain OF). The climate of studied region is semi-arid with 1350 meters altitude from sea level. Based on the soil test, pH was about 7.1, soil texture was loamy-sand and the depth of top soil was 70 cm. The experimental unit included six ridges of 25 cm in 6 m length. The plant density was 40 plants per m2. Each 1 gram bacteria have 107 no, we therefore used about 7 gr from each bacterium for seed inoculation. We also used Arabic gum to adhere the bacteria to the seed.
Results and Discussion: The results showed that the planting date had a significant effect on all characteristics, except brain to grain ratio and the ratio of skin to grain. The effect of seed inoculation with plant growth promoting rhizobacteria was statistically significant on plant height, stem diameter, number of main and sub main branches, seed oil and protein percentage. The maximum number of boll per plant, number of grain per boll, 1000-grain weight, grain yield, biological yield, harvest index, plant height and protein percent were achieved on the first planting date (5 April). The lowest amounts of these traits were obtained on the third planting date (5 May). The maximum oil percentage, number of primary and secondary branches and stem diameter were obtained on the first planting date and seed inoculation by Azotobacter. The lowest rates of these traits were obtained on the third planting date and no inoculation. Thus, seed priming with Azotobacter and first date (5 March) planting are recommendable to increase number of grain per boll, 1000-grain weight, grain yield, biological yield, harvest index, plant height and protein percent and other traits.
