Effect of Biochar and Microbial Inoculation on P, Fe, and Zn Bioavailability in a Calcareous Soil

To identify effective ways of increasing the yield of crops grown in nutrient-poor calcareous soils, the combined effects of biochar addition and inoculation with plant growth promoting rhizobacteria (PGPR) and arbuscular mycorrhizal fungi (AMF) on wheat growth and soil properties were investigated under rhizobox conditions. Measured soil properties included pH, electrical conductivity (EC), organic matter content (OM), the availability of P, Fe, and Zn in the rhizosphere, and the uptake of these elements by plants. Combined biochar addition and microbial inoculation were shown to significantly increase the concentration of available forms of P, Fe, and Zn in the soil when compared to non-biochar treatments. The highest soil pH (7.82) was observed following biochar addition without microbial inoculation. The EC following biochar addition and PGPR inoculation was significantly higher than the other treatments, and the soil OM content was highest when combining AMF inoculation with biochar addition. The available P content after AMF inoculation combined with biochar addition was 27.81% higher than the control conditions, and AMF inoculation increased Fe and Zn bioavailability by factors of 2.38 and 1.29, respectively, when combined with biochar addition relative to AMF inoculation alone. The simultaneous biochar addition and PGPR inoculation significantly increased P uptake by the plants. The highest shoot Fe and Zn uptake rates were observed after a simultaneous application of biochar and PGPR inoculation. Under these conditions, shoot uptake was higher than seen when combining biochar addition with AMF inoculation by factors of 1.64 and 1.21, respectively. In general, it can be concluded that combining inoculation with growth-promoting bacteria and biochar addition can effectively improve nutrient availability to plant and soil conditions

Improving Phosphorus Availability and Wheat Yield in Saline Soil of the Lake Urmia Basin through Enriched Biochar and Microbial Inoculation

To reduce requirements for conventional chemical fertilizer and alleviate salinity stress in soils, a glasshouse experiment was conducted to assess the effects of enriched biochar on phosphatase activity, microbial respiration and wheat yield in non-saline and saline soils from the Lake Urmia basin (electrical conductivities 2 dS.m(-1) and 15 dS.m(-1), respectively). Nine treatments were tested: control, 1:1 mixture of apple and grape biochars (BC), phosphate solubilizing bacteria (PSB), BC plus PSB (BC-PSB), BC plus rock phosphate (BC-RP), BC enriched by rock phosphate and bacteria (BC-RP-PSB), BC enriched by rock phosphate and HCl (BC-RP-HCl) or H3PO4 (BC-RP-H3PO4) and chemical fertilizer (TSP). The addition of enriched biochar decreased the soil pH (by 0.5-0.9 units) and increased available phosphorus (>7-fold). In both the saline and non-saline soils, the highest alkaline phosphatase activity was obtained for BC-H3PO4-RP and BC-HCl-RP. Wheat growth parameters were reclaimed after enriched biochar application, indicating superior dry matter yields compared to the control and non-enriched biochar treatments and significantly higher yields compared to TSP. Beneficial effects on soil pH, phosphatase activity, soil respiration and biomass yield demonstrated that enriched biochar could partly substitute chemical fertilizers and increase plant growth in salt stress conditions. However, further field studies are needed to understand the benefits of enriched biochar in different soils and climates

Optimization of Biofertilizer Formulation for Phosphorus Solubilizing by Pseudomonas fluorescens Ur21 via Response Surface Methodology

This study aimed to analyze and quantify the effect of different ratios of vermicompost, phosphate rock, and sulfur on P solubilization and release by Pseudomonas fluorescens Ur21, and to identify optimal levels of those variables for an efficient biofertilizer. Twenty experiments were defined by surface response methodology based on a central composite design (CCD), and the effects of various quantities of vermicompost, phosphate rock, and sulfur (encoded by -1, 0, or +1) on P solubilization was explored. The results show that the CCD model had high efficiency for predicting P solubilization (R-2 = 0.9035). The strongest effects of the included variables on the observed P solubilization were linear effects of sulfur and organic matter (vermicompost), a quadratic effect of phosphate rock, and an interactive effect of organic matter x phosphate rock. Statistical analysis of the coefficients in the CCD model revealed that vermicompost, vermicompost x phosphate rock, and phosphate rock x phosphate rock treatments increased P solubilization. The optimal predicted composition for maximal P solubilization by P. fluorescens Ur21 (at 1684.39 mg.kg(-1), with more than 90% of the added phosphate dissolved) was 58.8% vermicompost, 35.3% phosphate rock, and 5.8% sulfur. ANOVA analysis confirmed the model's accuracy and validity in terms of F value (10.41), p value (<0.001), and non-significant lack of fit

Interactions between Biochar and Compost Treatment and Mycorrhizal Fungi to Improve the Qualitative Properties of a Calcareous Soil under Rhizobox Conditions

Most calcareous soils have relatively low levels of organic matter. To evaluate the effect of pruning waste biochar (PWB) and pruning waste compost (PWC) combined with arbuscular mycorrhizal fungi (AMF) on the biological indices, a rhizobox study on wheat using a completely randomized design was conducted under greenhouse conditions. The studied factors included the source of organic material (PWB, PWC, and control), the microbial inoculation (+AMF or -AMF), and the zone (rhizosphere and non-rhizosphere soil). At the end of the plant growth period, organic carbon (OC), microbial biomass carbon (MBC), microbial biomass phosphorous (MBP), microbial respiration (BR), substrate-induced respiration (SIR), and alkaline (ALP) and acid (ACP) phosphatase enzyme activities in the rhizosphere and non-rhizosphere soils were determined. Simultaneous application of a source of organic matter and AMF inoculation significantly increased the OC and biological indices of soil relative to those observed when applying organic matter without AMF inoculation. Additionally, MBC, MBP, ACP, and ALP enzymes activities in the rhizosphere zone were significantly higher than in the non-rhizosphere. AMF increased BR and SIR levels in the rhizosphere by 13.06% and 7.95% compared to those in the non-rhizosphere, respectively. It can be concluded that PWC and PWB can improve soil biological properties by increasing microbial activity

Harnessing the Potential of Symbiotic Endophytic Fungi and Plant Growth-Promoting Rhizobacteria to Enhance Soil Quality in Saline Soils

Soil salinity is one of the most important abiotic stresses limiting crop growth and production worldwide. Some microorganisms can improve the plants' tolerance to salinity. For this purpose, a greenhouse experiment was performed to understand the influence of various microorganisms on soil biological indices and wheat growth under different saline conditions. The factors varied in the experiment were the microbial treatment (rhizobacteria, mycorrhizal fungi, endophytic fungus, and control) and salinity stress (0.5, 8, and 14 dS m(-1)). Rhizobacteria were isolated from saline soils, but the fungi were prepared from a microbial bank. Overall, ten isolates were purified, and three with promising growth-promoting properties were identified using phenotypic and molecular methods. The selected isolates belonged to the genera Pseudomonas (P. aeruginosa Ur83 and P. fluorescens Ur67) and Stenotrophomonas (S. maltophilia Ur52). Soil quality indices were found to decrease with increasing salinity, but inoculation with microorganisms alleviated this decline. Inoculation with plant growth-promoting rhizobacteria (PGPRs) increased basal respiration, substrate-induced respiration, microbial biomass carbon, acid and alkaline phosphatase activities, and carbon availability by factors of 1.37, 1.27, 1.83, 3.07, 1.29, and 1.11, respectively. These results show that inoculation with symbiotic microorganisms can improve agricultural soil quality under saline conditions and may thus be valuable in agriculture

Influence of PGPR Bacteria and Arbuscular Mycorrhizal Fungi on Growth and some Physiological Parameters of Onopordon acanthium in a Cd-Contaminated Soil

Introduction: Heavy metals (HMs) are serious threat for environment due to their dangerous effects. These metals as contaminants that can be accumulated in soil and after absorption by plants, finally will be found in food chains. Cadmium (Cd) is one of the dangerous HMs that threats the health of plants, living organisms and human. Physicochemical remediation methods may cause large changes in different characteristics of soils . Recently environmental-friendly strategies including phytoremediation have been emphasized by researchers. Phytoremediation that refers to the use of plants and their assistance with microorganisms for remediation of contaminated soils is an effective and low cost method for reclamation of heavy metals polluted soils. The most important limitation of phytoremediation is low availability of heavy metals and sensitivity of plants to contamination. There are evidences that soil microbes can help to overcome these limitations through several ways. Plant growth promoting rhizobacteria (PGPR) and arbuscular mycorrhizal fungi (AMF) are known to enhance plant growth and survival in heavy metal contaminated soils through different mechanisms including producing promoting metabolites, auxin, siderophore and antibiotics. In this study the role of some strains of PGPR (a mixture of Pseudomonas species including P. putida, P. fluorescens, and P. aeruginosa) and AMF (a mixture of Glomus species including G. intraradices, G. mosseae and G. fasciculatum), on uptake and accumulation of Cd, Fe, Zn and Cu as well as some physiological properties of Onopordon (Onopordon acanthium L) were evaluated. Materials and Methods:This study was carried out under greenhouse condition as a factorial experiment based on a randomized complete block design with two factors including Cd concentration (four levels) and microbial treatment (three levels) in three replications. Consequently, a soil was selected and spiked uniformly with different concentrations of Cd (0, 10, 30 and 100 mg Cd kg-1 soil) at greenhouse of agricultural college in Urmia University. The contaminated soils were then sterilized and subsequently inoculated with arbuscular mycorrhizal fungi (a mixture of Glomose species including G. intraradices, G. mosseae and G. fasciculatum) and plant growth promoting rhizobacteria (a mixture of Pseudomonas species includeing P. putida, P. fluorescens, and P. aeruginosa). The seeds of Onopordon plants were grown in 2.5 kilogram pots under greenhouse condition. At the end of growing season the shoot dry weight, Cd, Fe, Zn and Cu concentration and element contents and some of physiological parameters of plant as well as microbial properties were analyzed. Furthermore, the effect of soil Pb level on population, activity and efficiency of the inoculated microbes was studied. Results and Discussion: Significant difference was observed for plants’ dry weights. At different Cd levels, the yield of inoculated plants was higher than that of control plants. Furthermore, at elevated Cd concentration, plant height, biomass, relative yield, chlorophyll a, b, carotenoids, relative water content (RWC) decreased significantly (P < 0.05), however, plants inoculated with plant growth promoting rhizobacteria and arbuscular mycorrhizal fungi showed considerable amount of dry matter, chlorophyll a, b as well as RWC. Mycorrizal and bacterial inoculation and Cd treatment also had significant effect on leaf photosynthetic pigments concentration and plant relative water content. In general, concentrations of photosynthetic pigments and RWC were higher in inoculated plants at every level of soil Cd. The microbial inoculation effectively decreased the inhibitory effects of Cd on plant growth. Shoot yield of arbuscular mycorrhizal fungi and plant growth promoting rhizobacteria plants increased by 2.7 and 2.1 times as well as microbial respiration increased by 2.17 and 2.01 times compared to control treatment. The results showed inoculated plant absorbed more Cd than non-inoculated plants. Plant growth promoting rhizobacteria were more effective than arbuscular mycorrhizal fungi inoculation in shoot Cd concentration. Cd contamination reduced soil microbial population and basal respiration. Results showed that with increasing soil Cd concentration shoot Fe, Zn and Cu concentrations significantly decreased. Root colonization rates decreased significantly with 10 mg kg-1 Cd addition for AMF treatments, and drastically with 100 mg kg-1 Cd added. Plant roots in the control and PGPR treatment were not colonized. Conclusion: It is concluded that plant growth promoting rhizobacteria and arbuscular mycorrhizal fungi inoculation could be sustained and promoted plant growth in phytoremediation processes. Therefore, under Cd contamination it can be use PGPR and AMF as growth promoters and finally enhance phytoremediation efficiency

Salinity-induced differences in soil microbial communities around the hypersaline Lake Urmia

Lake Urmia in north-western Iran is one of the largest hypersaline lakes in the world, and agricultural production in the surrounding area is limited by soil salinity. We investigated the effects of salinity on belowground microbial communities in soils collected from fields of cultivated onions (Allium cepa L.) and lucerne (Medicago sativa L.), and sites with the native halophyte samphire (Salicornia europaea L.). We tested the hypotheses that salinity reduces microbial biomass and changes the structure of the microbial community. The physical and chemical properties of soil samples were analysed, and phospholipid fatty acids were identified as signatures for various microbial groups. We found that the organic carbon (OC) content was the dominant determinant of microbial biomass. We also found linear relationships between OC and the biomass of various groups of organisms across the wide salinity gradient studied. Salinity, on the other hand, caused changes in the microbial fatty acid composition that indicated adaptation to stress and favoured saprotrophic fungi over bacteria, and Gram-negative bacteria over Gram-positive. Principal component analysis showed that salinity variables and microbial stress indices formed one group, and OC and microbial biomass another. The importance of OC for high microbial biomass in severely stressed soils indicates that OC amendment may be used to mitigate salt stress and as a method of managing saline soils

Isolation and Identification of Insoluble Zinc-Solubilising Bacteria and Evaluation of Their Ability to Solubilise Various Zinc Minerals

Zinc (Zn) is an important trace element that is essential for optimal plant growth. Zinc-solubilising bacteria can release Zn from its insoluble compounds. We isolated and identified Zn-solubilising bacteria (ZnSB) from the rhizosphere, and semi-quantitively and quantitatively evaluated their ability to dissolve various Zn minerals (ZnO, ZnCO3 and Zn3(PO4)2). Out of 24 rhizosphere soil samples, 15 strains of Zn-solubilising bacteria were isolated and purified. Five isolates that were found to be the most efficient in solubilising insoluble Zn compounds were identified based on gene 16S rRNA sequencing. Three of the isolates belonged to the genus of Pseudomonas, and two to Enterobacter. The highest solubilisation index among the three insoluble Zn compounds was observed in Pseudomonas putida (3.31) in the culture medium containing ZnO. Among the three tested insoluble compounds, the highest mean solubility by the strains was obtained from ZnO, followed by ZnCO3, and Zn3(PO4)2, respectively. The highest rate of Zn release among the three insoluble compounds was obtained in the culture medium of the Pseudomonas fluorescence strain Ur22 (35.6 mg L−1), which was ten times as great as that of the background solubilisation observed in the sterile control culture medium (3.8 mg L−1). Zn solubilisation was associated with a strong pH decrease in the culture medium, the strongest for Pseudomonas fluorescence (Ur21), which lowered pH to 4.2 compared to the control at pH 6.8. We concluded that the identification of effective ZnSB, and their use as bio-fertiliser, will help improve plant nutrition and production

Improving Phosphorus Availability and Wheat Yield in Saline Soil of the Lake Urmia Basin through Enriched Biochar and Microbial Inoculation

To reduce requirements for conventional chemical fertilizer and alleviate salinity stress in soils, a glasshouse experiment was conducted to assess the effects of enriched biochar on phosphatase activity, microbial respiration and wheat yield in non-saline and saline soils from the Lake Urmia basin (electrical conductivities 2 dS.m−1 and 15 dS.m−1, respectively). Nine treatments were tested: control, 1:1 mixture of apple and grape biochars (BC), phosphate solubilizing bacteria (PSB), BC plus PSB (BC-PSB), BC plus rock phosphate (BC-RP), BC enriched by rock phosphate and bacteria (BC-RP-PSB), BC enriched by rock phosphate and HCl (BC-RP-HCl) or H3PO4 (BC-RP-H3PO4) and chemical fertilizer (TSP). The addition of enriched biochar decreased the soil pH (by 0.5–0.9 units) and increased available phosphorus (>7-fold). In both the saline and non-saline soils, the highest alkaline phosphatase activity was obtained for BC-H3PO4-RP and BC-HCl-RP. Wheat growth parameters were reclaimed after enriched biochar application, indicating superior dry matter yields compared to the control and non-enriched biochar treatments and significantly higher yields compared to TSP. Beneficial effects on soil pH, phosphatase activity, soil respiration and biomass yield demonstrated that enriched biochar could partly substitute chemical fertilizers and increase plant growth in salt stress conditions. However, further field studies are needed to understand the benefits of enriched biochar in different soils and climates

Abundance of arbuscular mycorrhizal fungi in relation to soil salinity around Lake Urmia in northern Iran analyzed by use of lipid biomarkers and microscopy

Saline soils around Lake Urmia in northern Iran constitute a stressed environment for plants and microbial communities, including arbuscular mycorrhizal (AM) fungi. Soil and root samples were collected from fields cultivated with the glycophytes Allium cepa L. and Medicago sativa L, and sites dominated by the halophyte Salicornia europaea L. Soil and root samples were analyzed for the AM fungal signature neutral lipid fatty acid (NLFA) 16:1 omega 5. The roots were also examined microscopically for mycorrhizal colonization. Each plant species was sampled across a salt gradient. Microscopic examination showed no AM fungal structures in the roots of S. europaea. The highest root colonization was recorded for M. sativa. The highest NLFA 16:1 omega 5 values were found in soil around M. sativa roots and the lowest in soil around S. europaea roots. We found evidence for stimulation of vesicle formation at moderate salinity levels in M. sativa, which is an indication of increased carbon allocation to mycorrhiza. On the other hand, we found a negative correlation between salinity and arbuscule formation in A. cepa, which may indicate a less functional symbiosis in saline soils. (C) 2013 Elsevier GmbH. All rights reserved