مجله زیست شناسی خاک
سال یازدهم شماره 1 (بهار و تابستان 1402)

Salt stress and boron toxicity in the soils of arid and semi-arid regions of the world limit plant growth. A factorial experiment in a completely randomized design with three replications was used to investigate the effect of arbuscular mycorrhizal fungus on the growth and nutrient uptake of maize under salinity stress and boron toxicity. Two levels of boron (control and 30 mg B kg-1), two salinity levels (control and 8 dS m-1) from the source of boric acid and sodium chloride and two fungal levels (without inoculation, inoculation with Claroideoglomus etunicatum fungus) were considered. The results showed that salinity stress and boron toxicity had no effect on root colonization percentage (P>0.05). At the level of 30 mg B kg-1 boron, the fungus significantly increased the chlorophyll index, shoot boron, potassium, and phosphorus uptake (7.09%, 15.83%, 31.62%, and 51.57% respectively) and significantly decreased root boron, iron, copper and manganese uptake, (35.15%, 28.72%, 39.62% and 42.12% respectively). At the level of 8 dSm-1, the fungus significantly increased the amount of chlorophyll, copper, and manganese uptake, (5.05%, 35.38%, 25.97% respectively) and significantly decreased sodium uptake (40.31%). Under combined stress conditions and in the presence of fungus, chlorophyll index, root boron, potassium, phosphorus, and iron uptake, (8.42%, 61.56%, 82.01%, and 23.63% respectively) were significantly  increased but shoot sodium, zinc, copper, and boron absorption, (20.98%, 40.07% 72.54% and 34.38% respectively) were significantly decreased. The results of this research indicated that inoculation of fungus could help to improve the growth and absorption of nutrients in conditions of boron toxicity and soil salinity stress.

There are many sources of saline water that can be used in agriculture by adopting specific methods. Considering that salinity stress reduces the growth of plants, including wheat, Therefore, any technology that increases wheat's tolerance to salinity stress is very important. The use of plant growth promoting rhizobacteria (PGPR) is one of the strategies based on sustainable development to reduce the effects of stress in agricultural production. In this research, five strains of selected PGPR were used which were screened based on different plant growth stimulating characteristics. The ability of the strains to salinity tolerance at electrical conductivity (EC) values of 5, 10, 15 and 20 dS.m-1 was evaluated. A factorial greenhouse experiment was conducted based on the completely randomized design in three replicates under salinity stress conditions during a period of 100 days using wheat cultivar Narin in the year 2020 at the central station of the Soil and Water Research Institute. Salinity stress was applied through irrigation with saline water at four levels with electrical conductivity of 0.40 (normal water), 6, 10 and 14 dS.m-1. The inoculation factor included levels without inoculation and inoculation with Pseudomonas putida P186, P. fluorescens P187, P. sp P241, Azotobacter chroococcum Azto478 and A443 and Azospirillum lipoferum strains. Two milliliters of inoculum per seed was inoculated with a population of 1.5 x 108 during cultivation. The laboratory results showed that all strains did not show any growth reduction up to a salinity of 20 dS.m-1. The results of the greenhouse experiment showed that irrigation with saline water had significant reducing effects on all growth indices. Stress at the levels of 6, 10 and 14 14 dS.m-1 caused a decrease of 13.5, 35 and 57% of shoot wet weight, respectively. Also, the mentioned levels caused a decrease of 37.5, 50 and 55% of shoot dry weight, respectively. The root dry weight decreased by 80, 87 and 91%. Plant height decreased by 11, 17, and 18%, head length by 16, 25, and 31%, and head number by 23, 31, and 45%, respectively, at different salinity levels. Inoculation with selected bacteria did not show a significant effect on any of the wheat growth indices under salinity stress conditions. In this research, it was concluded that the reasons for the lack of significant effect of inoculation could be the resistance of the Narin variety to salinity and the inability of the bacteria to make the plant more tolerant to salinity conditions or the growth-promoting properties of the bacteria being unaffected in these conditions.

In order to evaluate the compost traits and casing soil inoculated with bacteria on the mushroom growth and yield, a study was conducted as randomized complete block experiment with three replications during 1400 year in Mushroom Company of Nagin Fasle Shahrekord. The treatments included bacteria inoculated into the casing soil (Azotobacter chroococcum, Pseudomonas putida, Azospirillum lipoferum, Bacillus subtilis, Enterobacter cloacae and cyanobacteria) and controls. Chemical and biological properties of compost during different stages of composting including microbial respiration, microbial population, organic carbon, dissolved organic carbon in cold and hot water, ash, amount of lignocellulose compounds, acidity and electrical conductivity and mushroom growth indicators were measured including mushroom weight, yield, biological efficiency and production rate. Results of this study indicated that the chemical and biological properties of compost changed during the composting process. The highest microbial activity was observed at beginning of phase II, and also the highest bacterial population (1.25 × 109 CFU.g-1) was found. Bacterial population in casing soil was lower than compost. The amount of hemicellulose ranged from 22.6 to 45.1 percent, and the amount of cellulose ranged from 16.7 to 42.2 percent, and the amount of lignin ranged from 17.7 to 33.7 percent. Bacteria inoculation to the casing soil showed a positive effect on the yield (15.9%) and the average weight of mushroom (18.0%) compared to the control (p≤0.05). Among the bacteria used, Azotobacter crococcum and Pseudomonas putida showed a better effect on the functional characteristics of the mushroom than the other bacteria. Therefore, more research is needed to determine strategies to increase the yield and quality of agricultural traits in the commercial cultivation of edible mushrooms.

This study was carried out in order to investigate the biodiversity of arbuscular mycorrhizal fungi (AMF) in natural oak forest, broad-leaved plantation, needle-leaved plantation, agricultural and rangeland land uses in Lene habitat, Chardavol city, Ilam province. For this purpose, five mixed soil samples were randomly collected from each land use at soil depths of 0-5 and 5-15 cm and the characteristics of soil and AMF were investigated. Wet sieving and sucrose method were used to extract AMF and their identification was done based on spore morphological characteristics such as shape, color, size, number of wall layers, thickness of wall layers and hypha shape. Totally 19 AMF species belonging to eight genera including Glomus, Acaulospora, Claroideoglomus, Rhizophagus, Septoglomus, Dentiscutata, Paraglomus, Entrophospora were identified. The results showed that spores abundance and biodiversity of AMF were different in different land uses. The highest spore density was related to natural forest (78.12), broadleaf forestry (66.28) and pasture (57.48), and the lowest was related to agriculture (50.96) and needle-leaved plantation (28.16). It was also found that the abundance of symbiotic AMF was the highest in the natural forest (16.6) and rangeland (15.8) and the lowest in the agricultural (11.6) and needle-leaved plantation (14.4) land uses. Shannon-Weiner and Simpson's diversity indices in natural forest, rangeland and plantation were significantly higher than agricultural land use. According to the results, there was no significant difference between the two depths of soil samples in spore density and biodiversity indices. The results also showed that the change in land use had negative effect on the diversity and abundance of symbiotic AMF. Therefore, to preserve biodiversity of AMF, it is recommended that natural forests be under more protection.

Waste tire rubber (WTR) contain significant amounts of zinc (Zn) and they are potential sources of Zn for plants. This study was carried out to investigate the effect of Zn-dissolving Pseudomonas isolates and WTR on growth characteristics and Zn and Fe concentrations of the corn plant. An experiment was conducted in a completely randomized design with factorial arrangement with three replications in a sterile sand -culture in green house condition. The experimental factors include Pseudomonas bacteria at six levels (without inoculation (C) and inoculation with five isolates (B1 to B5)) and Zn treatment from the WTR source at four levels of 0 (C), 100 (T1), 200 (T2) and 300 (T3) mg Zn per kg (equivalent to 0, 9, 18 and 27 g WTR per kg of sand respectively). The results showed that the main effects of the treatments on Photosynthetic performance index, chlorophyll content of leaves, Chlorophyll fluorescence and shoot dry weight were significant. The amount of each of these parameters increased in all bacterial and WTR treatments. The use of WTR (18 g/kg) along with inoculation of isolates increased all measured parameters compared to the control. Root dry weight and zinc concentration in shoots and roots, were affected by the interaction of treatments. The highest amount of plant dry weight was observed in B3+T3 treatment (2.14 fold increase compared to the control (. The concentration of zinc in the plant shoots was the highest in the B4+T3 treatment, which was 20 times higher than the control. The highest concentration of zinc in the root was observed in the presence of isolates B3 and B2 in WTR (18 g/kg) treatment which was 25 and 22 times higher than the control, respectively. The highest concentration of iron in the shoots and roots of the plant was related to the WTR (18 g/kg) treatment with the amount of 28.3 and 30.7 mg kg-1, respectively. The bacterial isolates increased the iron concentration of shoot compared to the control, but no significant difference was observed between the isolates.

Heavy metal accumulation in soils has been become one of the most dangerous environmental issues in human societies. The use of a cheap and safe technology such as phytoremediation with a proper symbiosis between plants and plant growth-promoting microorganisms, can be an effective step in phytoremediation technology. In the present study, the effects of individual and combined inoculation of Serendipita indica and Sinorhizobium meliloti on alfalfa grown in a contaminated soil with different concentrations of zinc (0, 400 and 800 mg kg−1 soil) were investigated. The results showed that the highest level of zinc contamination led to a significant decrease of 53.3%, 71%, 25.2% and 60.2 of shoot and root dry weight, Phosphorus concentration, and plant catalase enzyme respectively, it was also associated with an increase of 174.5, 56.6, 60.2 and 36.6% in the amount of hydrogen peroxide, malondialdehyde, peroxidase and superoxide desmutase enzymes. The combined inoculation of fungi and bacteria increased phosphorus absorption in the plant. In addition, this treatment reduced the transfer of zinc from the roots to the shoots and stimulated the system of plant oxidative enzymes such as catalase and reduced the amount of hydrogen peroxide and malondialdehyde, which increased the growth characteristics of the plant. Therefore, the combined inoculation of fungi and bacteria has an important role in alfalfa plant nutrition by reducing the pH of the rhizosphere soil and increasing the Zn absorption and increasing the Zn stabilization in alfalfa roots.

In order to study the effect of bioactivator application to accelerate the production of compost from sugarcane wastes, an experiment was conducted as a complete randomized design with four replications in Safiabad Agricultural Research and Education and Natural Resources Center in 2020 (for one year). The treatments included: control (bagasse without the use of bioactivator) and the second to fourth treatment were the application of 0.5, 1 and 1.5% by weight of bioactivators in 100 kg bagasse, respectively. The results showed that, there was a significant difference between treatments at significance level of 5% in the terms of electrical conductivity (EC), organic carbon (OC), C/N (in sampling after 45 days) and Fe and Mn concentrations (in sampling after 60 days). Furthermore there was a significant difference between treatments at the level of 1% in terms of OC, C/N and Cu concentration (in sampling after 60 days). Studies also showed that the highest temperature (52 °C) was measured in 1.5 % treatment and the highest EC was measured in sampling after 45 days in 1% treatment (3.02 dS/m). The highest OC and C/N, were measured in sampling after 60 days (43.9% and 34.4) in 1.5 % treatment, respectively. Regarding the amount of elements in the final compost (in sampling after 60 days), the highest amount of Fe concentration (4581.5 mg. kg-1) was measured in 1 % treatment, Cu (15.25 mg. kg-1) and Mn (72.25 mg. kg-1) were measured in 1.5 % treatment and no significant difference was observed among the treatments in terms of nitrogen, phosphorus, potassium and zinc (Zn) concentrations at significance level of 5%. According to results of this study, the 1.5% treatment increase the speed and quality of compost produced from sugarcane waste (bagasse).