مجله زیست شناسی خاک
سال هشتم شماره 1 (بهار 1399)

Cadmium, because of the long half a lifetime in the human and animal body and its toxicity, has great importance in agriculture. Today, plant growth-promoting rhizobacteria (PGPR) are used to increase the bioavailability and uptake of heavy metals in polluted soils. This study aimed to investigate the effectiveness of cadmium-tolerant fluorescent pseudomonads with inorganic phosphate solubilizing ability on the cadmium uptake by maize plants in contaminated soil. For this purpose, a greenhouse experiment was conducted in factorial based on a completely randomized design with four replications. Treatments were included four levels of bacteria (without bacteria (P0) and inoculation with three isolates P1, P169, P108) and four levels of time after planting (3, 6, 9, and 12 weeks). The soils were artificially spiked with cadmium (13 mg kg−1) as Cd(NO3)2. The results showed that the inoculation of maize with the selected isolates significantly increased shoot and root dry weights and shoot cadmium uptake in comparison to non-inoculated plants. The maximum shoot dry weight observed in plants inoculated with P169 and 12 weeks (31.22% more compared to non-inoculated plants). In the 12th week after planting, there was not any significant difference among P1, P108, and P169 isolates in shoot dry weights. P1 and P108 enhanced shoot dry weights by 23.81 and 22.21 percent in comparison to control, respectively. The maximum uptake of cadmium in plant shoot was found in inoculation with P169 and 12th week. In the 12th week, P169 increased cadmium uptake of the shoot by 150 percent in comparison to the control and 13.81 and 37.75 percent, compared to P1 and P108, respectively. Although all of the isolates used in the greenhouse experiment significantly increased cadmium uptake by maize plants but the effectiveness of P169 was more evident than other isolates.

Residue retention with less soil disturbance is a promising approach to maintain the soil quality. The study was conducted to determine the effects of tillage at three levels (conventional tillage (CT), reduced tillage (RT), and No-Till (NT)) as main plots and crop residue at two levels (residue removal and retention) as sub-plot on phosphatase and urease enzyme activitiesof calcareous soil in wheat-corn cropping system based on a split-plot design with three replications at the Zarghan in Fars province, Iran from 2015-16 to 2016-17. Results showed that applying tillage and residue significantly affected on soil bulk density (BD), organic matter (OM), and enzyme activities. In soil surface (soil depth: 0-10 cm), the highest BD was observed by NT practice when residue removed, whereas BD maximized as soil depth (10-20 cm) increased especially under CT. In contrast, OM was maximized under RT and residue retention (30% of residue) in wheat-corn rotation. The lowest alkaline phosphatase enzyme (917.00 and 443.00 µg PNP g-1 soil h-1 in wheat and corn, respectively) was obtained by CT and residue removal. Applying RT with 30% of residue was maximized acid phosphatase activity in wheat by 442.65 µg PNP g-1 soil h-1 and followed in corn by 374.17 µg PNP g-1 soil h-1. However, the highest urease enzyme activity (198.33 and 181.67 µg NH4 g-1 soil h-1 in corn and wheat, respectively) observed by NT when 30% of residue was retained. In general, adopting RT practice accompanied by retaining crop residue (30% of residue on the soil surface) to reduce BD, increase OM and improve enzyme activities of calcareous soil in the wheat-corn cropping system is recommended.

Heavy metals are one of the pollutants in the ecosystem. They are of great importance due to their specific physiological effects on living organisms, even at low concentrations. Cadmium is one of the most important heavy metals due to its high mobility in the soil, and high solubility in water and soil. For this purpose, a pot experiment was carried out in a completely randomized design with factorial arrangement and two factors and three replications at the Faculty of Agriculture, Ferdowsi University of Mashhad, to evaluate the growth characteristics, membrane stability, relative water content and uptake of some nutrients in coriander (Coriandrum sativum L.) under heavy metal stress and mycorrhizal inoculation. The first factor was cadmium nitrate in 4 levels of 0, 40, 20, 80 mg/kg soil, and the second factor was mycorrhiza in 3 levels (without fungi inoculant, Funnetiformis mosseae, and Rhizophagus intraradicese). The results showed that with increasing stress levels, the membrane stability index, root colonization percentage, and the concentration of nitrogen, phosphorus, potassium, calcium, iron, and zinc in coriander were significantly reduced. While increasing cadmium concentration in soil, increased significantly cadmium concentration and relative water content of leaf (p ≤ 0.01). However, the mycorrhiza inoculation reduced the harmful effects of cadmium in the plant. The highest concentrations of nitrogen (3.08%), phosphorus (0.126%), calcium (2.92%), magnesium (0.85%), and zinc (121 mg/kg) were observed in mycorrhizal fungi application. Funnetiformis mosseae was more effective than Rhizophagus intraradices with a 42% decrease in cadmium concentration of leaf at the highest level of soil cadmium contamination (80 mg/kg cadmium nitrate). Inoculation with mycorrhizal fungi (especially Funnetiformis mosseae) increased plant tolerance against cadmium stress. So, plants inoculated with mycorrhizal fungi had higher growth and yield than non-inoculated plants, and their application in these conditions is recommended.

This study was aimed to isolate and identify the most efficient native bacteria from warm-water fish farms of Mazandaran that can potentially oxidize hydrogen sulfide. After sampling the sediments and sediment pore water of fish farms in Fereydunkenar, Babol, Babolsar and Sari counties, enrichment and isolation carried out in three liquid culture media of Starkey, Postgate, and H-3 to increase the number of the desired microorganisms. After isolation based on morphological difference (in the above solid culture media), 27 isolates (14 autotrophic and 13 heterotrophic isolates) were purified. Then preliminary screening was performed based on pH decrease in Starkey liquid culture media, among which only 6 isolates were selected. In the next stage, the amount of thiosulfate consumption, sulfate production, and the density of bacteria in Starkey liquid culture media were measured to a more detailed evaluation of the ability of sulfur oxidation. Among the 6 isolates, isolates FH-13, FH-21, and FH-14 had the highest oxidation ability of thiosulfate ions (4053.79, 3104.5, and 2878.97 mg / l for 14 days) and sulfate ion production (2240, 965 and 490 mg / l) in the liquid culture medium. Molecular identification of these isolates was performed using the 16S rRNA gene sequencing method. The results showed that three isolates FH-14, FH-13, and FH-21 had 99.70, 100, and 99.80% of identity with the Thiobacillus thioparus HM173634, respectively. Based on the results of this study, these strains can be used as effective sulfur-oxidizing strains in the bioremediation process to remove hydrogen sulfide in warm-water fish farms.

Acenaphthene, a natural component of crude oil, is a carcinogenic compound and persistent to degradation. Bioremediation, which involves the use of living microorganisms for degradation and mineralization of contaminants, used to remove persistent contaminants such as Acenaphthene. Complete degradation of hydrocarbons is the result of different species activity that is known as a bacterial consortium. On the other hand, the low solubility of oil pollutants is a limiting factor in bioremediation. So, recently biosurfactant-producing bacterial consortia have been considered in the bioremediation to increase the bioavailability of oil contaminants. In the present study, Asenaphthene degrading bacteria were isolated by enriching the oil-contaminated soil and then, the biosurfactant-producing bacteria were screened based on the surface tension of the medium containing the isolates. After bacterial identification, degradation of Acenaphthene by isolates, consortium, and extracted biosurfactants from isolates, were investigated in the aqueous medium and soil. The results showed that both AP3 and BM1 could decompose Acenaphthene and produce biosurfactants. The AP3, BM1, and their consortium degraded 72.2%, 54%, and 100% of pollutants in the aqueous medium, respectively. The effect of biosurfactant extracted from AP3 on the degradation of Acenaphthene was more than the BM1 biosurfactant. Percentage of Acenaphthene degradation in soil by AP3 and consortium was 64.7% and 75.7% respectively, and the use of AP3 biosurfactant with the consortium led to complete degradation. 16S rRNA gene sequences of isolates showed that AP3 100% was compatible with Bacillus velezensis CR-502 (T) and BM1 99.5% was compatible with Pseudomonas putida ATCC 12633. Therefore, the use of a consortium and biosurfactants improve the biodegradation of Acenaphthene compared to inoculation of individual isolates.

Nowadays, extensive application of antibiotics in medicine for treating people and in agriculture and veterinary caused soil and water contamination and also have negative impacts on soil microorganisms and biological processes rate. In the present study, the effect of releasing the mostly used antibiotic in soil (gentamicin, oxytetracycline, and penicillin) and different concentrations (50, 100 and 200 mg/kg dry soil) with and without organic and mineral conditioner (cow manure, biochar, and nano-zeolite) on total soil fungi, total cultivable bacteria and coliforms and their resistance and resilience indices at three time periods including 1-7, 7-30 and 30-90 days during a 90-day incubation time was evaluated in a split-factorial design which soil conditioners were considered as main plots and antibiotic types and concentration were as experimental factors. Resistance and resilience indices were calculated for microbial groups, as well. The addition of antibiotics, including gentamicin, reduced the abundance of microorganisms. Based on the results, cow manure had the highest total fungi count at 1-7 days which had no significant difference with biochar application. At 7-30 days, total bacteria count in antibiotic-treated soil significantly increased which the increase rate for gentamicin and oxytetracycline, especially at higher concentrations was more than penicillin. At 7-30 and 30-90 days, the application of cow manure and gentamicin and oxytetracycline at 100 and 200 mg/kg soil resulted in the highest total coliforms count. Generally, the results of the present study showed that the application of conditioners, especially cow manure, could decrease the toxic effects of antibiotics in soils and causes an increase in resistance and resilience indices of soil microorganisms.

One of the most important results of human industrial activities is the increased concentration of heavy metals in the soil. Application of mycorrhizal symbiosis is one of the bioremediation methods of heavy metals contaminated soils. The purpose of this study was to investigate the potential of mycorrhizal fungi in lead phytoremediation by Cerasus mahaleb in soil contaminated with different levels of lead. The treatments were three levels of mycorrhizal fungi and three levels of soil contaminated with lead in four replications. The results showed that the percentage of root colonization decreased by increasing soil contamination with lead. Also, in the highest level of soil contamination, the mixed mycorrhizal treatment had the highest percentage of root colonization. The transfer factor (TF) of lead in stems and leaves in the soil with high contamination was more than low contamination. Mixed mycorrhizal treatmentshowed the highest effect in lead transfer to leaf and stem. The highest bioconcentration factor (BCF) and bioaccumulation coefficient (BAC) were related to soil with high contamination. Also, the mixed mycorrhizal treatment had the best performance in increasing BCF and BAC. The amount of BCF was greater than BAC and TF and was close to one (0.9). Although  C. mahaleb seedlings could accumulate lead in roots and transfer it to shoot, they effectively stabilized lead in root and thus decreased lead translocation from soil to plant shoot.

This study aimed to investigate the effect of five herbicides (Tribenuron-methyl, Metribuzin, Trifluoralin, Haloxyfop-methyl, and 2, 4-D (on the soil dehydrogenase and urease activities.

The experiment was conducted as a completely randomized design with five herbicides and a control with three replicates for six months and the enzyme activities were measured at beginning of the experiment, and after three and six months. The concentration of herbicides was 0.27, 0.67, 0.67, 0.67, and 0.1 mg/kg soil for Haloxyfop-methyl, Metribuzin, Trifluoralin, 2, 4-D, and Tribenuron-methyl, respectively.

The results showed that the effect of herbicides on the enzyme activities was significantly different (p0.01). After 3 months, the herbicides decreased the urease activity in comparison to the control (34.9 µgN.g-1). The most reduction was related to Trifluoralin (24.8 µgN.g-1) which was 28.9% lower than the control. Urease activity increased after six months compared to three months, and this increase was 41.5% for Trifluoralin herbicides (35.1 µgN.g-1). Urease activity in control treatment in six months was not significant compared to the three months. All of the herbicides significantly reduced the dehydrogenase activity after three months compared to the control (0.6 µgTPF.g-1), so that the dehydrogenase activity was observed in Haloxyfop treatment with 0.01 µgTPF.g-1, which was 98% lower than the control. In all treatments, dehydrogenase activity after six months was significantly higher than that in the three months, so that the highest dehydrogenase activity was observed in 2,4-D treatment (1.44 µgTPF.g-1), which was significantly higher than the control.

The results show that the herbicides significantly decreased the activity of the enzymes compared to the control during the three months. After six months the enzyme activities recovered to the level before herbicides application. Probably this was due to a short lifetime of herbicide in the soil which was less than six months.