مجله زیست شناسی خاک
سال نهم شماره 2 (پاییز و زمستان 1400)

Phosphorus is one of the essential elements for plant growth and increase in the availability of indigenous phosphorus have an effective role in reducing the chemical fertilizers consumption. This study was conducted to investigate some inoculant formulations for phosphate-solubilizing fluorescent pseudomonads for agricultural and environmental uses. For this purpose, 30 isolates belong to fluorescent pseudomonad group were collected from microbial bank of Faculty of Agriculture of Vali-e-asr University of Rarsanjan. Then ability of all isolates for solubilizing tricalcium phosphate were studied. In addition, the ability of those isolates for increasing phosphorus availability in soil amended with and without phosphate rock at 15, 30 and 60 days was inspected. Finally, the persistence of the selected isolate was evaluated in some inoculant formulations. The results indicated that all isolates were able to increase the solubility of tricalcium phosphate in solid and liquid media of PKV and the pH of culture medium also decreased significantly. The maximum and minimum phosphate solubilization in solid media of PKV were related to isolates D33 and D24 and in liquid media, it was related to isolates D6 and D4 respectively. The results showed that isolates D33 and D35 increased the soil phosphorus bioavailability in 15, 30, 60 day after inoculation by 48, 25, 75% and 72, 50, 26% respectively. The cell numbers of D33 and D35 isolates in three inoculant formulations including talcum powder, talcum+rice bran and talcum+sawdust (180 days after inoculation) indicated that maximum and minimum of cell numbers of D33 were occurred in talcum powder and talcum+rice bran (105 cfu/g) and talcum+sawdust (8×103 cfu/g)  respectively. Maximum and minimum of cell numbers of D35 were observed in talcum+rice bran (105 cfu/g) and talcum+sawdust (10 cfu/g) respectively. Finally, inoculant formulation of talcum+rice bran was able to maintained an acceptable cell numbers of both isolates D33 and D35 (106 cfu/g) at the end of 150 days.

Deforestation and poor farming practices are two factors that seriously threaten natural resources and seriously damage the soil productivity. This study was conducted to investigate the effects of deforestation and land use on some chemical and microbial properties of soil in different layers of evangelical forest, Citrus Garden and wheat farm soils in Sari township. Organic matter content, total nitrogen, carbon and nitrogen of microbial biomass were significantly reduced when evangelical forest converted to wheat farm (in all three layers) and citrus garden (in two layers of 0-10 and 10-20 cm). When evangelical forest converted to wheat farm (in first layer) organic matter, total nitrogen, carbon and nitrogen of microbial biomass were reduced 35.5, 51.2, 69.7 and 59.8%, respectively. Phosphorus availability and microbial respiration were significantly reduced when evangelical forest converted to wheat farm and citrus garden. The amount of reduction for phosphorus availability and microbial respiration were 85.2% and 35.1% respectively for the top layer of wheat farm. Microbial C/N was significantly reduced when evangelical forest transformed to wheat farm and microbial metabolic coefficient was significantly increased when evangelical forest changed to the two other land uses. The urease activity in both land use (citrus garden and wheat farm) and alkaline phosphatase activity were significantly reduced in wheat farm soils. The results of this study showed that changes in the chemical and microbial properties of the soil was more substantial when evangelical forest converted to agriculture land. The most important reasons for reduction of soil quality may be related to the harvesting (in both citrus garden and wheat farm) and the loss of the closed loop of forest, soil tillage (on the farm) and animal manure application.

Application of biochar and compost with bio-inoculants can improve the microbiological properties of the soil. In order to investigate the effect of apple pruning wastes biochar, compost application and bio-inoculants on some biological properties of soil, a pot experiment was performed as a factorial in a completely randomized design with 2 factors: (1) organic resources (control (without organic resources), biochar and compost) and (2) bio-inoculants (control (without bio-inoculants), plant growth-promoting bacteria (Pseudomonace fluorescens, Stenotrophomonas putida, Pseudomonace aeruginose), arbuscular mycorrhizal fungus (Glomus versiform, Glomus fasciculatum ,Glomus intraradices) and endophytic fungus (Priformosphora indica) under greenhouse conditions with three replications. At the end of the corn growth period (65 days), some microbiological properties such as bacterial respiration (BR), substrate-induced respiration (SIR), microbial biomass carbon (MBC), microbial population, carbon availability index (CAI), phosphatase and urease enzymes activity were measured in soil. The results showed that the addition of organic resources and microbial inoculation to the soil caused a significant increase in biological parameters compared to treatments without organic matter and microbial inoculation. The highest levels of BR, SIR, CAI and microbial population were observed in compost- plant growth-promoting bacteria treatments, which increased by 76.2, 33.3, 77.4 and 85.8%, respectively, compared to the control treatment (without organic matter and bio-inoculants). Addition of compost and biochar significantly increased the MBC and the urease activity compared to the control treatment (no organic resources). Simultaneous application of organic and biological treatments also increased the activity of acid and alkaline phosphatase compared to the control treatment. Generally, the application of organic matter and microbial inoculation improves the soil biological properties.

The presence of some microorganisms including actinomycetes or their metabolites increase the growth of fungal mycelium, roots colonization and plant growth indices. In this study, an experiment was carried out in a completely random design (CRD) with three replications. The effects of four actinomycete species (S. griseus, S. albogriseus, S.sp1 and S.sp2) were examined on the frequency of hyphae, vesicles and colonization of clover root (Trifolium alexandrinum) inoculated by Rhizophagus irregularis. Wet and dry weight and phosphorus concentrations were measured in shoot and root of clover. The results showed that mycorrhizal symbiosis greatly stimulated by S. albogriseus and root and shoot growth and phosphorus absorption significantly increased in shoot and root of clover. Three species of actinomycetes considerably improved the fungal organs frequency in clover root, and the percentage of root colonization increased from 48.61% (in control) to 86.59, 72.93% and 66.90% in S. albogriseus, S. griseus, and S. sp2 treatments respectively. The frequencies of hyphae in clover roots increased from 45.32% (in control) to 92.55, 85.48 and 71.47% S. albogriseus, S. griseus, and S. sp2 treatments respectively. Inoculation of mycorrhizal roots of clover with S. albogriseus significantly increased the wet and dry weight and phosphorus concentrations of clover roots and shoots but S. griseus and S. sp2 treatments increased shoot dry weight and phosphorus concentration in the roots and shoot of clover root. S. albogriseus could possibly be used in the production and preparation of R. irregularis inoculant.

Large areas of Iranian soils have different levels of salinity; so the crop production in those area is very limited. Azotobacter can stimulate plant growth by various mechanisms. Inoculation of plants with superior native isolates of Azotobacter that are compatible with saline areas may enhance plant growth under salinity stress. In this study, 20 isolates of Azotobacter isolated from Iranian soils were evaluated in terms of phosphate solubility, potassium releasing, auxin and siderophore production. Salinity tolerance of isolates was investigated in bacterial culture medium at electrical conductivity of 10, 20, 30, 40 and 50 dS.m-1. Six selected isolates at three levels of salinity were evaluated on maize Single Cross 704 in a factorial completely randomized block design with three replications in a greenhouse condition. Salinity stress was applied through irrigation water (0.36, 3 and 6 dS.m-1). The laboratory results revealed that Az63, Az69 and Az70 were the most effective isolates in terms of phosphate solubilization and potassium releasing and siderophore production. All isolates of Azotobacter grown very well in saline media with electrical conductivity of 10 dS.m-1 but some of them could grow in saline media with electrical conductivity of 20 dS.m-1. Az22 and Az66 isolates were more tolerant to salinity and they survive at electrical conductivity of 50 dS.m-1. The greenhouse results showed that dry weight of clusters increased 64 percent compared to the control when plant inoculated with Az69 isolate under normal irrigation water. Inoculation had no significant effect on growth indices when electrical conductivity of irrigation water was 3 or 6 dS.m-1. In this study, Az69 isolate was suggested for further studies.

Endophytes are microorganisms (bacteria or fungi or actinomycetes) that reside inside the internal tissues of plant with no negative effect on host plants. Endophytic bacteria trigger many positive effects on host plants. The aroma and flavor of strawberry fruit are important characteristics that is affected by endophytic bacteria such as Methylobacterium. Endophytic bacteria, are effective in the synthesis of carotenoids and the production of volatile and phenolic compounds. In addition, they are effective in producing the aromatic components in fruit. Endophytic bacterial frequency and genotype can be affected by host plant genotype, climatic and soil conditions. This study was carried out to isolate endophytic bacteria from two strawberry cultivars (Kurdistan and Parous) in three regions (Angouzan, Gavrood and Noshur) in Kurdistan province. For accurate identification of bacterial isolates, 16S-rRNA gene sequencing was used for identification of purified endophytic isolates and their frequency determined at different times of fruit ripening. The results revealed that the all endophytic bacterial isolates from both cultivars were belong to the genus Methylobacterium. The frequency of these bacteria was statistically different in two cultivars and in different sampling time. The frequency of Methylobacterium significantly was higher in Kurdistan cultivar compared to Parous cultivar in all three regions (p <0.05). The highest frequency of Methylobacterium was observed in the fruit ripening time. It seems that Methylobacterium and its frequency probably have an effect on the aroma and delicacy of these two varieties.

Chitosan is a natural and destructive polymer that consists of glucosamine units, which, due to reactive groups, can reduce the availability of heavy metals and change soil enzyme activities which is an indicator of soil quality. However, little information is available on simultaneous effect of chitosan and heavy metals on soil enzymes activities. In this study, the interaction of chitosan at three levels of control, low molecular weight (LMC), and high molecular weight (HMC) with Pb at three levels of 0, 50 and 500 mg/kg on available soil lead (Pb) investigated on activity of acid and alkaline phosphatase, L-glutaminase and fluorcine diacetate hydrolysis enzymes in two different soils, Lavark and Langroud. The results were statistically compared. Both chitosan types significantly reduced available Pb concentration in two soils, but HMC was more effective. In Lavark soil, LMC and HMC application to Pb treatments significantly increased the activity of acid and alkaline phosphatase, L-glutaminease and fluorcine diacetate hydrolysis compared to control treatments. In Langroud soil, LMC application to Pb treatments significantly increased L-glutaminease activity, but did not affect the activity of other enzymes. The HMC application in Langroud soil also did not significantly affect activity of any enzymes compared to control. Level of 50 mg/kg Pb in the presence of chitosan significantly decreased acid phosphatase activity in Lavark soil and hydrolysis of fluorcine diacetate hydrolysis in Langroud soil compared to control, but had a positive effect on the activity of other enzymes. Level of 500 mg/kg Pb in the presence of chitosan also reduced acid and alkaline phosphatase activity in Lavark soil and hydrolysis of fluorcine diacetate in Langroud soil, but significantly increased the activity of other enzymes. Generally, increasing or decreasing enzyme activity due to the simultaneous presence of chitosan and Pb depended on soil, enzyme, Pb concentration, and chitosan type.