An incubation experiment was conducted to study the effect of clay content and composition on organic nitrogen mineralization. The experiment measured the mineralization of organic nitrogen from ...alfalfa residues, enzyme activities, and microbial biomass nitrogen in mixtures of sand, kaolinite, and non-layered colloids (NLCs) with sand as a control. The study found that as the contents of kaolinite and NLCs increased, the mineralization of organic nitrogen and enzyme activity decreased, but microbial biomass nitrogen increased. The maximum decrease in organic nitrogen mineralization was 88.6%, and microbial biomass nitrogen increased from 4.7 to 15.5%. The acid and alkaline phosphatase activities also decreased by 86.0 and 93.6%, respectively, with an increase in clay content. The specific surface area (SSA) of the mixtures showed an inverse relationship with enzyme activity and mineralization of organic nitrogen. Inactivation of extracellular enzymes by adsorption on the surfaces of kaolinite and NLCs, and decreased accessibility of organic nitrogen substrate molecules due to adsorption, reduced the mineralization of organic nitrogen. Microbial biomass nitrogen increased as the water holding capacity of the mixtures increased, indicating the importance of water-filled pores in accommodating active microbial biomass and protecting it from desiccation and predators.
Thiobacillus
, as useful soil bacteria, plays an important role in sulfur cycling. The purpose of this study was to identify the species
Thiobacillus thioparus, Thiobacillus novellas
and
Thiobacillus ...denitrificans
in rainfed and irrigated lands soil in Ajabshir, Ilam, Qorveh, Rojintaak, Sonqor, Kermanshah and Research Farm of Razi University in Iran. Sampling was performed as randomized completely with three replications at depth of 0–30 cm. The
Thiobacillus
species were determined via 16S rRNA characteristics. The results of agarose gel electrophoresis indicated that
T. thioparus
was the highest amount in the irrigated land in Research Farm and its lowest amount was in the Rojintaak rainfed land. These species not found in four locations and conditions including the Ajabshir irrigated, Qorveh rainfed, Research Farm rainfed and Rojintaak irrigated lands. The results of the
T. novellas
indicated that this was found in Ilam irrigated, Qorveh rainfed, Research Farm irrigated, Rojintaak irrigated and Rojintaak rainfed lands. The highest and lowest amount of
T. novellas
was indicated in the Rojintaak and Ilam irrigated lands respectively. The
T. denitrificans
gene showed that this bacterium was observed only in both samples of Ajabshir. Our study showed that
Thiobacillus
was not detected in all of the soils. If sulfur fertilizer is given to the soil without this bacterium, it is necessary to use sulfur fertilizer with
Thiobacillus
bacteria inoculation for better sulfur oxidation.
In this study the effects of natural and long-term oil pollution levels (H: high, M: moderate and L: low) on the activity of lipase, β-glucosidase, urease, phosphatase, and dehydrogenase were ...analyzed. For this purpose, 120 oil-contaminated soil samples were collected from four locations located in oil-rich region of the west of Iran (Kermanshah province, Iran). After determining the physicochemical characteristics of soils, microbial counting and enzyme activities were measured. To determine the total bacterial population and bacteria involved in crude oil decomposition, bacterial counting was done in NA and CFMM culture media, respectively, which had a direct relationship with the increase in crude oil content. The average percentage of crude oil measured by Soxhlet method was 4.03%, 9.95% and 22.50% respectively for L, M and H levels. The results showed that the bacterial population increased with the increase of the contamination intensity. All the studied enzymes, except urease, had the highest activity in heavily polluted soils (H soil), and their lowest activity was observed in lightly polluted soils (L soils). Location 1 had the highest bacterial population as well as the highest activity of dehydrogenase (52.13 μg TPFg−1 h−1), acid phosphatase (35.86 μg PNPg−1 h−1), alkaline phosphatase (78.13 μg PNPg−1 h−1), lipase (92.58 μ MLA g−1 h−1) and β-glucosidase (21.67 μg PNPg−1 h−1) enzymes. In the soil samples of location 4, which had the lowest number of bacteria, the highest activity of urease enzyme (592.36 μg NH4g−1 h−1) was obtained. Principal components analysis (PCA) was also performed and 67% of the cumulative of the samples could be explained by the first two components (biochemical and physical). The findings of this research showed that natural and prolonged crude oil pollution caused the selection of oil-resistant microbial communities, and therefore we saw their positive response to the presence of oil compounds and increased enzyme activity other than urease activity.
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Dragon's head (Lallemantia iberica) is a rich source of alpha-linolenic acid, linoleic acid, essential oil, protein, and mucilage. Therefore, the aim of this study was to evaluate the effects of ...foliar application of three different concentrations of Fe and Zn (control, 4, and 8 g lit−1) at two different developmental stages (vegetative stage (VS) and reproductive stage (RS)) on the quantity and quality of dragon's head seed yield and fatty acid composition in two crop seasons (2018 and 2019) under two environments (normal irrigation as control (NI) and post-anthesis water deficit (WD). In NI, average yields of seed, oil, and protein were 1155, 340, and 183 kg ha−1, respectively, and in the WD, they were 879, 283, and 148 kg ha−1, respectively. By applying Zn and Fe, the mean values of seed, oil, and protein yields in the NI were 1425, 478, and 264 kg ha−1, while in the WD, they were 1011, 354, and 200 kg ha−1, respectively. Furthermore, the application of WD resulted in a significant increase in zinc concentration, protein percentage, and saturated fatty acid percentage in seeds. Unlike WD, iron and zinc treatments decreased the percentage of saturated fatty acids and increased the percentage of unsaturated fatty acids. The number of capsules per plant had the most positive indirect effect on grain yield. The results showed that foliar spraying of Fe and Zn could effectively mitigate the adverse effects of WD on the quality and quantity of seed and oil yield dragon's head.
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•Foliar application of Zn and Fe mitigated the adverse effect of water deficit.•Oil quality significantly decreased under water deficit environment.•Mucilage yield was more sensitive to water deficit than protein and oil yields.•Oil quality significantly increased under foliar application of Zn and Fe.•The number of capsule per plant had the most positive direct effect on grain yield.
Thiobacillus is a genus of Gram-negative, rod-shaped and autotrophic Betaproteobacteria. They catalyze the dissimilatory oxidation of elemental sulfur and reduced inorganic sulfur compounds. Whereas ...more than 30 species have been known in this genus, most were never reliably or effectively published. The rest were either reclassified into Thiomonas, Paracoccus, Starkeya, Sulfuriferula, Halothiobacillus, Thermithiobacillus or Acidithiobacillus, were lost from culture. Most of Thiobacillus species are obligate autotrophs via elementary sulfur, thiosulfate or polythionates as energy sources. Based on 16S ribosomal RNA sequence analysis, many members of Thiobacillus have been reclassified. A system was developed for the detection of Thiobacillus bacteria by the amplification of specific 16S ribosomal RNA sequence gene (16S rDNA) fragments with PCR. Primer sequences were designed for the amplification of fragments of 16S rDNA.
Salinity is a major abiotic stress that impacts crop productivity globally. Plant growth-promoting rhizobacteria (PGPRs) exploit several mechanisms to not only decrease soil salinity but also improve ...the systemic tolerance of plants to osmotic stress. In this work, the effect of five PGPR strains was investigated on the growth and physiological responses of tomato plants, including stomatal closure, proline, and K
+
and Na
+
content under a range of salt stress, 0, 2.5, 5, 7.5, and 10 dS m
−1
. The effect of PGPR strains and salinity levels on the soil biological characteristics was also investigated. Salt stress affected the plant growth and physiological factors and soil biological factors in a dose-dependent manner. The highest saline stress, 10 dS m
−1
, reduced shoot and root dry weight and root volume up to 51.3, 41.5, and 51.8%, respectively. It also increased stomatal resistance and proline content 2.01- and 3.66-folds and decreased K
+
/Na
+
ratio 4.16-folds, respectively. It also reduced basal respiration, substrate-induced respiration, and microbial biomass carbon up to 2.25-, 4.83-, and 6.7-folds and increased qCO2 3.18-folds, respectively. PGPR strains were able to modulate salt tolerance mechanisms, improve plant growth factors, and improve soil biological indicators.
Bacillus megaterium
P2 was the best strain in the balancing K
+
/Na
+
uptake at least at 10 dS m
−1
. However, the efficiency of strains was dependent on the magnitude of salt stress. Therefore, it is possible to introduce PGPR strains based on soil salt level or exploit rhizobacteria consortia to manage salt stress in different conditions.
IntroductionThe maintenance of planted forests in arid and semi-arid lands is important. Soil formation in forest ecosystems is different with different tree species. Tree species have a direct and ...indirect effect on soil organisms. Forest ecosystems change their species composition and abundance of microorganisms, and consequently their biogeochemical cycles. The accumulation of vegetation biomass and the improvement of soil fertility can play a significant role in soil restoration.Materials and MethodsIn order to investigate the biological characteristics of the soil from 5 treatments, including agricultural (dry farming and relatively poor lands that are usually cultivated barley and wheat and have low productivity), pasture (pastures with minimal vegetation and high slopes that are affected by overgrazing have been changed to barren lands), forest with Acacia type (under and outside the crown), forest with the Cupressus arizonica type (under and outside the crown) and forest with the Pinus brutia type (under and outside the crown) randomly. Sampling was done in 3 repetitions from the 0 to 5 cm layer. The statistical sampling design of this research was completely random, in which, according to the type of afforested species, two types of coniferous forest stands (including Cupressus arizonica and Pinus brutia) and one broadleaf stand (Acacia species) were selected. Also, the area under the crown trees and outside the crown trees was also investigated. Soil samples were sampled with sterile equipment and crushed through a 4-mm sieve. Fresh and moist soil was kept at 4 °C temperature for soil biological tests. Microbial biomass carbon, soil basal respiration (197 days), substrate-induced respiration, and metabolic quotient were measured. Streptomycin sulfate was used to measure fungal respiration and cycloheximide was used to measure bacterial respiration. The activities of urease, acid, and alkaline phosphatase enzymes were determined. After measuring the biological properties of the soil, the normality of the data was checked by the Anderson–Darling test, and the homogeneity of the variance of the treatments was checked by using Levene's test. Analysis of data variance was done using One-Way ANOVA and average data comparison was done using Duncan's test at 5 and 1% probability levels (SAS 9.4 and SPSS 26).Results and DiscussionThe results of soil biological characteristics analysis showed that the highest values of soil respiration and amount of consumed organic matter, substrate-induced respiration, microbial biomass carbon, enzyme activities, and fungal respiration were measured in conifers. Although the amount of these features was also significant in broadleaf trees, they had significant differences. In this study, the high soil respiration rate in coniferous covers compared to broadleaf can be due to the high organic carbon content of the soil in this cover. According to the results of substrate-induced respiration in different coatings, likely the activity of microorganisms involved in the decomposition of organic matter in the studied habitats had a significant difference; Therefore, different coatings can affect the population of soil microorganisms as the main source of decomposition and emission of carbon dioxide by changing the quantity and quality of organic matter and other factors. Also, the highest values of metabolic quotient and bacterial respiration were observed in agricultural and pasture covers. A higher metabolic quotient in these covers indicates a decrease in the efficiency of the use of leaf litter by the soil microbial community. In general, the metabolic quotient in the bacterial community is higher than the fungal community; Therefore, it seems that the predominance of the bacterial population in agricultural and pasture cover has caused this index to increase, although plowing and cultivation, and disturbance of these covers have caused stress to this bacterial community and as a result increased the metabolic quotient deficit in these covers.ConclusionThe results of this research showed that the type of planted tree species causes significant changes in the biological characteristics of the soil. The current research shows that the forest, whether coniferous or broadleaf, had the highest values of enzyme activities, basal respiration, substrate-induced respiration, microbial biomass carbon, and the lowest values of metabolic quotient compared to agricultural and pasture covers. Afforestation increases biological activity and possibly the number and diversity of microorganisms, and improves soil characteristics in the long term. In agriculture and pasture land, due to the destruction of soil and aggregates by agricultural activities such as plowing or excessive livestock grazing, the amount of organic carbon and the activity of microorganisms decreases, and with the decrease of other soil characteristics, the quality of the soil decreases over time. From this research, it can be concluded that the planting of forest species in the soils of degraded areas in the long term can increase soil organic carbon due to high-quality leaf litter, and as a result, increase permeability and soil moisture. Increasing soil organic carbon increases the activity of microorganisms, and in the long term, it will improve various soil characteristics. Planting forest plants in the natural areas of the country, which were destroyed due to the change of use to agriculture and indiscriminate cultivation and finally abandoned, can improve the characteristics of the soil and, as a result, establish the native vegetation of the region, and increase the permeability of water in the soil, the risk of soil erosion, floods, etc. reduce.
IntroductionCrude oil is a complex combination of many hydrocarbon and non-hydrocarbon compounds, including heavy metals, which affect the physical and chemical properties of the soil, cause the soil ...particles to stick and connect and then cause the soil to become stiff and impenetrable. Contamination of soil with petroleum hydrocarbons is a significant environmental problem, which has received remarkable attention in recent decades. Petroleum hydrocarbons are resistant and hazardous pollutants. Some petroleum hydrocarbons such as benzene are mutagenic and carcinogenic materials for humans. There are many physical and chemical methods to remediate oil-contaminated soils. Phytoremediation is a relatively new technology for refining contaminated soils in which resistant plants are used to remove or reduce the concentration of inorganic, radioactive, and organic pollutants, especially petroleum compounds, from the environment.Materials and MethodsSufficient amounts of about 50 kg of soil contaminated with petroleum hydrocarbons were collected from regions (0-30 cm soil depth) adjacent to the oil wells west of Kermanshah province. Uncontaminated soil samples were also taken from sites at the lowest distance to the contaminated sites. The aim of this study was to compare the efficiency of different plants to remove total petroleum hydrocarbons from oilfield soils. In this study, after determining the total amount of petroleum hydrocarbons, the contaminated and uncontaminated soils were mixed in 4 treatments with different weight ratios (0, 10, 25, and 35%). This experiment was established as completely randomized design with 3 replications for 6 different plants (Barley, Grass, Alfalfa, Hemp, Camelina, and Vicia ervilia). One treatment without plant was considered to remove soil matrix effects on petroleum hydrocarbon concentrations. Plants were harvested at the end of their growing season (90-120 days). Soils and plant samples from the experimental pots were analyzed for their important properties (including some physiological characteristics of the plants, as well as the percentage of reduced petroleum hydrocarbons in the soils). The gravimetric method was used to determine the concentration of petroleum hydrocarbons in the soil. After measuring the properties of the soil and plant, the normality of the data was checked by the Anderson–Darling test, and the homogeneity of the variance of the treatments was checked by using Levene's test. Analysis of data variance was done using ANOVA and average data comparison was done using LSD test at 5 and 1 percent probability levels (SAS 9.4 and SPSS 26).Results and DiscussionIn general, the growth of most plants showed a decreasing trend in proportion to the increase in soil pollution levels. However, the growth decline rates of different plants were not similar. Camelina was very sensitive to oil pollution and the plant could not tolerate pollution even at 10% level. After camelina, alfalfa was highly sensitive to oil pollution. The highest dry weight of the aerial parts of the hemp plant in the soil without oil contamination was observed at the rate of 111.22 grams in the pot. The leaf area of all studied plants in contaminated soils decreased compared to the control treatment (without contamination) so with the increase in the percentage of contamination, the leaf area of the plants was significantly reduced. The highest amount of leaf surface was observed in unpolluted soil and in the hemp plant. Except for the Camelina plant, which was completely destroyed at different levels of pollution, the rest of the plants showed a noticeable decrease in growth. The total petroleum hydrocarbons in soil were measured again 120 days after the start of cultivation, and its difference with the total amount of petroleum hydrocarbons at the beginning of cultivation was determined as the reduction of petroleum hydrocarbons and reported as a percentage. According to the mean comparison results, the percentage of reduced petroleum hydrocarbons was not significantly different among cultivated and non-cultivated treatments, although, it was significantly affected by soil pollution levels. Since all the studied soils contained natural bacteria and were not sterilized, the eliminated part of petroleum hydrocarbons is probably decomposed and removed by native bacteria in the soils. Therefore, the strengthening of native bacteria in these soils may increase the decomposition and degradation of petroleum hydrocarbons.ConclusionThe results of this research show that the presence of petroleum hydrocarbons in the soil caused a decrease in growth and other physiological characteristics in all studied plants. Although the Camelina was able to germinate in soils contaminated with petroleum hydrocarbons, the presence of these pollutants in the soil prevented the optimum growth of the plant, so its use in subsequent studies of phytoremediation of oil-contaminated soils, was not recommended. The results showed that there is no statistically significant difference between cultivated and non-cultivated treatments at different pollution levels, and the reduction of the total petroleum hydrocarbons in the soil was probably done by native microorganisms in the soil. It is recommended to take into consideration the efficiency of the plant species used, the type of polluting hydrocarbons, and the duration of contamination in future research to obtain better results.
Fertility islands are patches of soil beneath the trees and shrub's canopy and contain higher nutrient availability and water content than the surrounding areas in arid and semi-arid lands. Fertility ...islands are home to various soil organisms that play a crucial role in nutrient cycling. This study aimed to determine the influence of fertility islands beneath the coppiced oak trees on soil macrofauna diversity and biomass in semi-arid oak woodland. For this purpose, two main microhabitats, including beneath the patches of oak sprout-clumps (BPSC) and the interspaces (SBSC), were considered. Each microhabitat was divided into four classes with respect to the number of sprouts per sprout-clumps (N = 1–3, N = 3–10, N = 10–20, and N > 20) and distance gradient from the canopy (D = 0 m, D = 1–3 m, D = 3–5 m, and D > 5 m). Soil physical and chemical properties, soil macrofauna taxonomic group diversity, and biomass were measured for each microhabitat class. Most of the soil's physical and chemical properties, such as soil litter, soil organic carbon (SOC), available phosphorus (P), moisture content, and electrical conductivity (EC), were higher in BPSC than in SBSC. These properties were influenced by the structure (number of sprouts) of oak sprout-clumps and the distance gradient from the canopy. Soil macrofauna individuals (density), biomass, and diversity were higher in BPSC than in SBSC. A significant difference in soil macrofauna groups composition was found only at the canopy edge and was not affected by increasing distance from the canopy. The soil macrofauna diversity was positively correlated with soil moisture, SOC, and P. It was concluded that the sprout-clumps' structure influences the quality of fertility islands beneath the oak sprout-clumps and consequently dictates the variation of soil macrofauna composition and biomass.
•The structure of oak sprout-clumps controls fertility islands quality.•Increasing the spaces between the sprout-clumps magnify fertility islands effect.•The quality of fertility islands influences soil macrofauna diversity.•Gradient distances between the tree canopies influence soil macrofauna biomass.
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•Soil enzymatic activity generally decreased 1 year after fire but recovered with time.•Inversely the specific activity of enzyme increased 1 year after fire.•Microbial metabolic ...quotient (qCO2) also increased 1 year after fire.•Specific activity of enzymes is found the most fire responsive variable.
Fire is a major ecological factor altering soil properties that may remain for a long time. Little is known about the sensitivity to fire and post-fire recovery in soil microbial and biochemical properties in the semi-arid woodlands. The main objective of this study was to compare the changes in some microbial and biochemical properties in different years after fire. This study was conducted across a wildfire chronosequence in the semi-arid Zagros oak woodlands. We considered three fire treatments including 1, 3, and 10 years after fire. Then the soil samples were collected in a completely random design from each of the treatments. Soil microbial eco-physiological and enzymatic activities were measured for all the treatments and their relevant unburned control. The results indicated that soil organic carbon (Corg) decreased 1 year after fire (27%) and still remained lower for 3 years after fire (22%) and even for 10 years after (21%) compared to the controls. Microbial biomass carbon (Cmic) significantly decreased (77%) 1 year after the fire, whereas the value of basal respiration (BR) remained unchanged. The value of Cmic for the treatments 3 and 10 years after fire recovered to the unburned level. 1 year after the fire the ratio of BR to Cmic (qCO2) was three times as much as the control. Although the value of BR was lower (p < 0.05) for the treatment 3 years after the fire, the value of qCO2 was higher (p < 0.05) compared to the control. The value of absolute enzyme activities was generally lower (p < 0.05) 1 year after the fire. However, it recovered 3 years after the fire to the unburned level. In comparison to the absolute enzyme activity, the specific enzyme activity showed a different trend and generally increased 1 year after the fire. The absolute activity of acid phosphatase (ACP) was significantly lower (p < 0.05) 10 years after the fire, while the ratio of ACP/Corg was higher (p < 0.05) compared to the control. It was concluded that specific activity of enzymes are more efficient indicators to reveal the post-fire changes in soil quality in medium and long-term studies.
