Soil Biology, Biochemistry and Biotechnology
Marzieh Mazraeh; Roya Zalaghi; Naiemeh Enayatizamir
Abstract
Introduction Growth-stimulating bacteria are now proposed as an alternative to chemical fertilizers in order to increase soil fertility in sustainable agriculture. Biofertilizers are also expressed as microbial inoculants that are capable of removing soil nutrients from an inaccessible state through ...
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Introduction Growth-stimulating bacteria are now proposed as an alternative to chemical fertilizers in order to increase soil fertility in sustainable agriculture. Biofertilizers are also expressed as microbial inoculants that are capable of removing soil nutrients from an inaccessible state through biological processes. Plant Growth Promoting Bacteria (PGPRs) refer to a broad group of susceptible bacteria, which grow alongside the plant as the host and stimulate plant growth. On the other hand, these microorganisms in the soil are able to stimulate and improve biological indicators, such as microbial carbon biomass, microbial respiration, and microbial yield, and may also affect different forms of carbon in the soil. Among the PGPRs, it is possible to refer to Enterobacter and Pseudomonas. Pseudomonas are bacteria present in all agro-soils and have different growth-promoting characteristics. Enterobacteriaceae family is a large group of bacteria that are naturally present in the water, soil, and materials that are corrupted and contaminated. To evaluate the biological changes of soil due to the activity of PGPRs, biochemical parameters (microbial respiration and microbial carbon biomass) are usually monitored in the plant's rhizosphere. The rhizobox is one of the tools used to study the changes in the rhizosphere, by limiting the roots in a certain volume of soil and facilitating the sampling of rhizosphere soil. The aim of this study was to investigate the effect of plant growth-promoting bacteria on some biological and chemical properties of the soil under Rhizobox conditions. Materials and Methods In order to study some of the chemical and biological properties of the soil cultivated with maize and wheat and inoculated with growth promoting rhizobacteria (PGPR), a completely randomized design, including two maize and wheat plants and three levels of inoculation, including non-inoculated, Pseudomonas sp. strain Rhizo_9 and Enterobacter cloacae strain Rhizo_33 in three replications in Rhizobox pots was done in greenhouse conditions. At the end of the period, the plants were harvested and the dry weight of roots and shoots was measured. Also, 3 soil samples were sampled from each rhizobox, as follows: rhizosphere 1 (soil clinging to the root), rhizosphere 2 (1 cm soil clinging to mesh), and non-rhizosphere (soil far from the mesh). Some soil characteristics, including basal respiration, substrate induced respiration, metabolic quotient, and soil carbon components (soil organic carbon, microbial carbon biomass, cold-water-soluble carbon, hot-water-soluble carbon, and permanganate oxidable carbon) were measured. Results and Discussion Results showed that the amount of each carbon component, as well as basal and substrate-induced respiration in treatments with bacteria, was higher than non-bacterial treatments and these biological properties in the soil cultivated with maize were higher than those under wheat cultivation. According to the results, the highest amounts of the basal respiration (0.31 mg CO2 g-1 day-1), the substrate-induced respiration (1.65 mg CO2 g-1 day-1), the permanganate oxidable carbon (213.1 mg kg-1), and the microbial carbon biomass (17.53 mg 100g-1) were related to rhizosphere 1 soil of maize inoculated with Pseudomonas. The highest amounts of the organic carbon (0.82%), the cold-water-soluble carbon (1727 mg kg -1), and the hot-water-soluble carbon (955 mg kg-1) were related to rhizosphere 1 soil in maize inoculated with Enterobacter. This could show the differences between two bacteria in affecting on different forms of carbon in the soil. Conclusion The results of this study showed that maize had a higher effect on carbon forms of soil that could be because of higher root biomass and probably higher root secretions of maize in comparison to wheat. Also, by increasing the distance from plant roots (from rhizosphere1 soil to bulk soil), different forms of carbon decreased that showed the impact of rhizosphere (plant roots and rhizospheric microorganisms) on physicochemical and biological characteristics.Inoculation of PGPR bacteria caused an increase in soil respiration and soil different carbon forms but the two bacteria were different in increasing various forms of soil carbon that seems to be related to different secretions or different effects of bacteria or plant-bacteria associate on soil carbon forms. Although inoculation of Pseudomonas resulted in a higher amount of microbial carbon biomass, inoculation of Enterobacter resulted in higher amounts of cold-water-soluble carbon, hot-water-soluble carbon, and soil organic carbon. Also, the application of two PGPR bacteria (Enterobacter was more effective) increased root and shoot dry weights of maize and wheat compared to non-bacterial treatments.
Plant Nutrition, Soil Fertility and Fertilizers
Faranak Ghasemi; ُSaeid Hojati; Ahmad Landi; Roya Zalaghi
Abstract
Introduction Clay minerals are considered as the main source of ion exchange and storage of nutrients in the soil. Knowledge of change and transformation of minerals, in relation to plant nutrition, fixation and release of elements is important. Sepiolite and palygorskite are fibrous clay minerals widely ...
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Introduction Clay minerals are considered as the main source of ion exchange and storage of nutrients in the soil. Knowledge of change and transformation of minerals, in relation to plant nutrition, fixation and release of elements is important. Sepiolite and palygorskite are fibrous clay minerals widely distributed in arid and semi-arid soils. Both minerals are rich in Mg and therefore, their weathering can significantly affect the chemistry of Mg in soil. Biological weathering which is carried out by living organisms (i.e. plant roots, soil fungi and bacteria) plays an important role in providing nutrients to plants. Hence, the use of microorganisms such as mycorrhizal fungi in the rhizosphere of agricultural crops has become more widespread. In recent years several studies have been conducted in relation to the weathering of minerals in the rhizosphere soil. However, few studies in terms of mycorhizal symbiosis with plant roots were carried out on release of Mg from sepiolite and palygorskite. Therefore, a pot experiment with a factorial arrangement through a completely randomized design was conducted to identify how symbiosis of sorghum roots with Glomus mosae mycorhizae affects release of Mg from sepiolite and palygorskite. Materials and Methods Pots containing sterile quartz sand and sepiolite or palygorskite (25-53 µm) were prepared and fungal treatments including presence or absence of fungus Glomus mosae were applied to the pots and then sorghum seeds were sown. Johnson nutrient solutions containing magnesium and without magnesium were used to feed plants during 70 days of experiment. After harvesting, the chlorophyll content, plants height and stem diameter were measured by SPAD, tape measure and caliper, respectively. Afterwards, the roots and shoots were separated and plants biomass and the percentage of roots colonization determined. Then, plants were oven-dried, ground, and the magnesium contents of them after extraction with 1M hydrochloric acid were determined using Agilent 7000 ICP analyzer. The chemical composition of palygorskite, sepiolite, and quartz sand was determined using X-ray fluorescence (XRF) and their mineralogical composition was determined using X-ray diffraction (XRD) approach. Results and Discussion Analysis of variance for the main effect of treatments on plant height, stem diameter, shoot dry weight and root dry weight showed that the effect of different sources of magnesium on plant height, stem diameter and shoot dry weight was significant (P < 0.01). The highest and lowest height, stem diameter, root and shoot dry matter were found in treatments fed with complete Johnson solutions and the palygorskite, respectively. The results also illustrated that application of Glomus mosae symbiotic mycorhizae significantly increased plant height, stem diameter, and root and shoot dry matter compared with non-mycorhizal treatments. This could be attributed to the fact that Mycorrhizal fungi (Glomus mosae) absorb more water and nutrients through increased photosynthesis and plant growth, consequently leading to improved plant characteristics when compared with non-mycorhizal crops. The results also showed the highest percentage of root colonization in palygorskite treatments and the lowest one in control. In general, a symbiotic relationship is created to improve low nutrition of elements that the amount of them in the soilwith a little mobility. Therefore, anything that exacerbates this deficiency, leads to an increase in symbiosis between plants and fungi. On the other hand, When plant is faced with more nutrient deficiencies, the demand for a symbiothic fungusGlomus mosae increases. Besides, the greatest magnesium concentration and chlorophyll contents were found in control, sepiolite and palygorskite treatments, respectively. In all treatments, magnesium intake was sufficient to grow sorghum, but as the results show, the amount of magnesium in the control and that of sepiolite was much more than palygorskite. These results clearly show that sepiolite mineral is able to release more Mg than palygorskite. The results also showed that the presence of the fungus Glomus mosae has significantly affected the release of Mg from both minerals. Conclusion In both sepiolite and palygorskite treatments, magnesium and chlorophyll content increased in symbiosis with fungi. This shows the positive effect of Glomus mosae fungus on release of Mg from these two minerals, especially sepiolite. Although, both sepiolite and palygorskite were able to provide enough amounts of Mg for sorghum plants, however, it seems that in long-term Mg released from sepiolite can more easily meet the need of plants when compared with palygorskite.