مجله زیست شناسی خاک
سال یازدهم شماره 2 (پاییز و زمستان 1402)

The application of soil quality (SQ) in sustainable land management is evolving. However, despite their considerable importance, the inclusion of biological properties in soil quality assessments is limited due to the challenges and high costs associated with measuring these attributes. This study was carried out on the contribution of biological properties to soil quality. In this research, 22 physical, chemical, and biological properties of 90 surface soil samples (0-30 cm) were analyzed to determine the soil quality index (SQI) in the Honam region of Lorestan. Analyzed properties included pH, electrical conductivity (EC), organic carbon (OC), total neutralizing value, clay and silt content, microbial biomass carbon (MBC), basal microbial respiration (MR), the total fungal and bacterial populations, the populations of Azotobacter and Pseudomonas species, as well as the activities of urease, acid and alkaline phosphatase, the available potassium and phosphorus concentrations, the total nitrogen, and the content of manganese, iron, copper, and zinc. Principal component analysis (PCA) to select a minimum data set (MDS) revealed that eight principal components, each with eigenvalues greater than one, accounted for 89.83% of the total variance. Of the 22 soil properties 12 were selected for the MDS, with biological properties (5 properties) making a more significant contribution than the physical and chemical properties. The spatial distribution of the SQI underlines the significant influence of biological properties on soil quality. These results underline the importance of including biological properties in the assessment of soil quality.

The current average yield of button mushrooms is 17 to 20 kilograms per square meter. Increasing this yield to 22 to 27 kilograms per square meter could significantly enhance the economic viability and global competitiveness of mushroom production. Achieving this improvement requires a comprehensive understanding of the microbial dynamics in compost production and the nuanced nutrition of mushrooms, utilizing biological, organic, and chemical enhancers. A recent study utilized nine leading strains of the Pseudomonas genus, six strains of Bacillus subtilis, and five strains of Bacillus thuringiensis to promote growth and biocontrol capabilities. While no significant differences were observed among the strains, all Pseudomonas strains were found to effectively stimulate button mushroom mycelium growth, with strain P8 exhibiting the most pronounced growth-enhancement properties. Additionally, Bacillus subtilis strains S1 and S6 significantly boosted mycelium growth, and Bacillus thuringiensis strains T2, T3, and T5 supported mycelium growth. However, some strains (S2, S5, T1, and T4) inhibited button mushroom growth in certain mediums (PDA/NA + Extract medium). The most notable biocontrol effects were by strain S3 against the Trichoderma and strain S6 against the Mycogone fungus, each inhibiting growth with a maximum colony zone diameter of 20 millimeters, whereas strain T5 showed the least biocontrol effect. Given the beneficial and diverse effects exhibited by the species from the two genera studied, these findings suggest that employing a consortium of these bacteria as a biofertilizer could significantly enhance button mushroom production outcomes.

Phosphorus plays a crucial role in aquatic ecosystems, serving as a vital nutrient that promotes the growth and enrichment of freshwater environments, particularly in warm-water fish ponds. It exists in various forms within aquatic systems, both soluble and insoluble. Cyanobacteria, a diverse group of oxygen-producing, photosynthetic prokaryotes, possess phosphatase activities that convert phosphorus into a soluble form. Thus, this study aimed to isolate, identify, and examine the phosphorus-dissolving capabilities of cyanobacteria found in fish culture ponds at a laboratory scale. The study evaluated the phosphorus dissolution efficiency of four cyanobacterial strains isolated from warm-water fish ponds: Chroococcus sp., Oscillatoria sp., Microcystis sp., and Gloeocapsa sp., using two phosphorus sources, tricalcium phosphate and calcium phytate, in both floating surface and biomass portions. The findings indicated that Microcystis sp. was particularly effective, dissolving 47.5 mg/liter of tricalcium phosphate and 67.3 mg/liter of calcium phytate in the floating portion. In the biomass, Gloeocapsa sp. demonstrated the highest efficiency in dissolving phosphorus from both tricalcium phosphate and calcium phytate, with concentrations of 35.5 mg/liter and 18.7 mg/liter, respectively. However, the study observed no significant difference in cyanobacterial growth under varying phosphorus concentrations and sources across the experimental groups. The research highlights that certain cyanobacteria isolated from fish culture ponds possess the capacity to dissolve phosphorus to a notable extent when provided with sufficient sources of insoluble phosphorus.

Soil salinity and sodicity disrupt the balance of nutrients in the soil and create restrictions on plant growth. An experiment was conducted to evaluate the application of sulfur along with Thiobacillus bacteria and plant growth-promoting bacteria isolated from saline-sodic soils on the performance and concentration of micronutrients in wheat (Chamran cultivar) in saline-sodic soils in a factorial design within a completely randomized design, in three replications in greenhouse condition. The experimental factors included three types of saline-sodic soil (S1: SAR=13 and EC=8 dS m^-1), (S2: SAR=15 and EC=10 dS m^-1), and (S3: SAR=17 and EC=14 dS m^-1), four levels of plant growth-promoting bacteria (B0: control, Pseudomonas alcaliphila, Rhizobium pusense, and Bacillus subtilis) and two levels of sulfur along with Thiobacillus thiooxidans bacteria (T0: no application and T1: application of 31.4 grams per pot (10 tons per hectare) of powdered sulfur along with T. thiooxidans bacteria). Based on the sequencing of the 16S rRNA gene, the superior plant growth-promoting bacteria were identified as Pseudomonas alcaliphila, Bacillus subtilis, and Rhizobium pusense. The results showed that adding sulfur along with T. thiooxidans bacteria and other plant growth-promoting bacteria at different levels of salinity and sodicity led to an increase in grain yield and concentration of micronutrients compared to the control. At the salinity and sodicity levels of S1 and S3, the highest grain yield was observed in plants inoculated with R. pusense bacteria (13.1% and 88.8%, respectively). The combination of plant growth-promoting bacteria and sulfur along with T. thiooxidans bacteria did not have a significant effect on grain yield and concentration of micronutrients in saline-sodic soils. Overall, the individual application of R. pusense bacteria isolated from saline-sodic soils and sulfur along with T. thiooxidans bacteria plays a significant role in improving the performance and concentration of micronutrients in wheat in saline-sodic soils.

Salmonella is a common and persistent pathogen in soil environments, posing a significant threat to safe food production worldwide. Given the vital role of soil in agriculture, it is crucial to be cautious about the spread of Salmonella in soil and to employ effective methods for its detection and control. The increasing prevalence of Salmonella can be attributed to the rapid expansion of agriculture and industry, leading to the contamination of fertilizers and water sources with the bacterium. The survival of Salmonella in soil is influenced by various physical, chemical, and biological factors, leading to the continuous colonization of plant organs. Consequently, given the importance of healthy agricultural products, there is an increasing demand for new methods to investigate and identify bacteria in these foods. Several techniques exist for the identification of harmful bacteria in soil. However, using nanosensors as an advanced tool for bacterial detection is very promising, as it can effectively overcome the limitations of other methods. This review study examines the mechanisms of Salmonella contamination in soil and its interaction with plants, highlighting the importance of using biosensors for faster and more accurate detection of this bacterium in soil.

Oil pollution is one of the most critical environmental contaminations that can affect soil's biological, physical, and chemical properties. To investigate the effects of long-term and natural oil pollution on soil microbial respiration, including basal respiration (BR) and substrate-induced respiration (SIR), and beta-glucosidase enzyme activity, 120 oil-contaminated soil samples were collected from 0-15 cm depth in the oil-rich region of Naft-Shahr in Kermanshah province with three pollution levels: high (H), moderate (M), and low (L). After measuring the physical and chemical properties of the soils, the total bacteria and oil-degrading bacteria were counted on NA and CFMM culture media, respectively. This finding showed a positive and significant correlation between microbial population and oil concentration. The average oil percentage measured by Soxhlet extraction was 4.03%, 9.95%, and 22.50% for L, M, and H levels, respectively. The results showed that with the increase in oil concentration in soil samples, BR and SIR increased, and the highest BR and SIR respiration rates were 0.053 and 0.234 (mgCO2.g-1.h-1) in H soils, respectively. The measured beta-glucosidase activity was also higher in the presence of oil pollutants, with the highest activity (24.78 µgPNP.g-1.h-1) in H soils and the lowest (6.09 µgPNP.g-1.h-1) in L soils. Finally, a Principal Component Analysis (PCA) was conducted, and the results showed that 72% of the variance among samples could be explained by the first two components (biochemical and physical components). Oil pollutants that are naturally present in the soil for an extended period lead to the adaptation of pollution-resistant microbial communities over time, increasing their abundance, microbial respiration, and the activity of enzymes such as beta-glucosidase.