Journal of Soil and Plant Interactions

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Zinc (Zn) deficiency is one of the most widespread micronutrients deficiencies in plants that causes severe reduction in their growth and yield. An increase in reactive oxygen species (ROS) levels and a decrease in efficiency of detoxification mechanisms may be the major reasons for impairment of various cellular functions in Zn-deficient plants. This study was conducted in order to investigate the effects of individual and simultaneous inoculation of endophytic fungus, Piriformospora indica, and plant growth-promoting rhizobacterium, Azotobacter chroococcum, on biochemical properties, antioxidant enzyme activities and growth of wheat plant (Niknejad cultivar) in Zn deficiency and sufficiency conditions. The experiment was conducted in greenhouse of the Soilless Culture Center of Isfahan University of Technology by using the sterile sand-perlite (2:1 v/v) medium, as factorial in a completely randomized design with three replications. The results showed that Zn deficiency decreased shoot dry weight, carotenoids' content, total amount of Zn in shoot and antioxidant enzyme activities in control treatment (plants were not inoculated with fungi and bacteria). Inoculation of individual and simultaneous of P. indica and A. chroococcum resulted in increase of shoot dry weight at Zn deficiency condition. However, the highest shoot dry weight belonged to individual inoculation of A. chroococcum. Inoculated plants with P. indica had the highest total amount of Zn in shoot and concentration of carotenoids at both levels of Zn. Whereas, individual inoculation of A. chroococcum and also in combination with P. indica had only significant effect on increasing the total amount of Zn in shoot at Zn deficiency condition. Inoculation of A. chroococcum alone and also in combination with P. indica resulted in inducing antioxidant enzyme activities of ascorbate peroxidase and peroxidase in response to Zn deficiency. Whereas, individual inoculation of P. indica resulted in increasing and decreasing the activities of peroxidase and ascorbate peroxidase, respectively. In general, inoculation of wheat plant (Niknejad cultivar) with the studied microorganisms in this research, particularly inoculation of A. chroococcum, can serve as a useful method for alleviating deleterious effects of Zn deficiency stress.

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Information about the effect of endophytic fungus Piriformospora indica on wheat response to stress conditions is very limited and sometime contradictory. This greenhouse research was conducted in a hydroponic culture to investigate the inoculation effects of mycorrizhal-like fungus, P. indica, on enzymatic and non–enzymatic defense mechanisms of wheat (Triticum aestivum L., cv. Niknejad) at two levels of phosphorus (P) supply (deficient and sufficient). The experiment was factorial, based on a completely randomized design with three replications. Sixty days after applying the treatments, plants were harvested and shoot dry weight and concentration of P, iron, zinc and activity of antioxidant enzymes like catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPX) and chlorophyll a, b and carotenoids contents were measured. Results showed that P-deficiency reduced shoot dry weight and concentration of P and iron and increased concentration of zinc in the shoots. Inoculation of wheat roots with P. indica in P-deficiency condition resulted in significant increasing of shoot dry weight and P concentration. Also, chlorophyll a, b contents and concentration of carotenoids in P-deficiency condition was significantly higher than P-sufficiency condition. Inoculation of P. indica to wheat roots decreased chorophyll a, b contents and concentration of carotenoids. Inoculation of P. indica in P-deficiency condition significantly decreased the activity of GPX and significantly increased the activity of CAT and GPX in P-sufficiency condition. In general, inoculation of fungus P. indica to wheat plant could be recommended as an effective method to alleviate deleterious effects of P-deficiency and increase its tolerance to this stress.

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In order to determine the critical period for weed control of greenhouse cucumber, an experiment was conducted in 2012 in a soil greenhouse located 25 km from Mashhad, as a randomized complete blocks design with three replications. The experiment consisted of two treatment series of weed interference. The first series consisted of weed-interference periods (including 14, 28, 42, 56, 70 and 84 days after emergence and the entire growth period of greenhouse cucumber) and the second series consisted of weed-free periods (including 14, 28, 42, 56, 70 and 84 days after emergence and the whole period of greenhouse cucumber growth). Results of this study showed that red root pigweed, common purslane, black nightshade, dwarf mallowand and common lambsquarters were the weeds with the highest density and biomass. Increasing or decreasing the weed-interference and weed-free periods led to changes in density, biomass, relative density and relative biomass of these plants. If 10, 5, and 1% of greenhouse cucumber yield loss are acceptable, then weed control must be carried out from 23 to 77 days (54 days), 18 to 94 days (76 days), and 16 to 107 days (91 days) after the greenhouse cucumber emerges, respectively. In general, the results of this experiment demonstrated that weed control in greenhouse cucumber production is necessary to achieve optimal yield.

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Abstract
Recently, with the rapid growth of industry and agriculture, the contamination of agricultural soils with the cadmium (Cd) and microplastic particles has become a serious issue. Simultaneous presence of microplastics and Cd in soil can cause various biological effects, especially in the early stages of plant growth. In this research, the effect of Cd stress in the presence of polyvinyl chloride (PVC) microplastic particles was investigated in the early stages of the growth of foxtail millet (Setaria italica L., cv. Bastan). The experiment was arranged in a factorial according to the completely randomized design with three replicates based on five concentrations of Cd (0, 50, 100, 150, and 200 µM) and PVC microplastic (0, 1, 2, 4, and 6%). The studied traits included percentage and inhibition of germination, rate and mean germination time, seedling vigor index, weight of mobilized seed reserve, seed reserve utilization efficiency, seed reserve depletion percentage, relative seed germination, seedling toxicity level, germination tolerance index and root tolerance index. The results showed that both pollutants led to the decrease of most germination indices, however, certain concentrations of PVC with Cd stress improved the desired indices. So that germination percentage and seed reserve utilization efficiency in 200 µM Cd concentration with 1% of PVC increased by 43.2 and 206%, respectively, compared to the concentration of 200 µM Cd alone. The highest inhibition of germination percentage belonged to 200 μM Cd concentration, which was reduced by 52.4% with the application of 1% microplastic. Although PVC microplastic particles had adverse effects on the germination process of foxtail millet seeds, but in the presence of Cd in the soil, low concentrations of PVC can have some moderating effects on Cd toxicity.

Background and Objective: Simultaneous contamination of soil with microplastics and heavy metals may pose a more severe threat to the soil and plants than the contamination of one of them alone (Wang et al., 2021). Due to their high adsorption capacity and carrier effect, microplastics can change the accessibility and toxicity of co-existing environmental pollutants in soil organisms and plants. Therefore, our objective was to investigate the possible effect of PVC and Cd on Cd toxicity, germination, and growth characteristics of seedlings. 

Methods: The factorial completely randomized design experiment with three replicates was conducted. The seeds disinfected with 5% hypochlorite were placed in a sterile petri dish with 20 ml of 0, 50, 100, 150, 200 µM Cd and 0, 1, 2, 4, and 6% PVC and were kept at 25°C for seven days. The seeds were counted once every 24 hours until the seventh day. Then, the root and shoot lengths were measured in centimeters. Each of the seedling parts was separated from each other, oven-dried at 70°C for 48 hours and weighed. Germination percentage, germination rate, seedling vigor index, mean germination time, weight of mobilized seed reserve, seed reserve utilization efficiency, seed reserve depletion percentage, root tolerance index, relative seed germination, germination tolerance index, seedling toxicity level and germination inhibition percentage were calculated. Data were analyzed through the SAS (v. 9.4) statistical program, and means values were compared by LSD test (p < 0.05).

Results: The effect of Cd and PVC on the examined traits was significant at the 1% probability level, except for the germination percentage, which was significant at the 5% probability level. The effect of Cd and PVC on the relative seed germination was not significant. The presence of PVC with Cd improved the percentage of germination, the mean germination time, and the seedling vigor index. The presence of microplastic decreased the adverse conditions of Cd stress and reduced the toxicity level and germination inhibition percentage. Heavy metals can be adsorbed by microplastic particles, which could reduce Cd adverse effects during germination (Yang et al., 2019). However, co-exposure of microplastic and Cd led to a decrease in germination rate. Duan et al. (2018) stated that the simultaneous presence of Cd and microplastic causes the accumulation of pollutants in plant cells and the intensification of oxidative stress, which leads to higher toxicity. The average germination time reduction in the presence of PVC under Cd stress. Due to the increased concentration of pollutants, disturbances were observed in the weight of mobilized seed reserve, seed reserve utilization efficiency, and seed reserve depletion percentage. Under the heavy metals stress, the starch mobility was reduced, and following the reduction of the mobility of seed reserves, the weight of the transferred seed reserves decreased (Seneviratne et al., 2019). Microplastics prevent water and nutrient absorption by the seeds, then delay germination and root growth (Bosker et al., 2019). The presence of microplastics moderated the adverse conditions of Cd stress and reduced the toxicity level, and germination inhibition percentage.

Conclusions: The PVC application moderated the Cd stress and improved the germination tolerance index as a crucial parameter of plant tolerance to stress. Therefore, despite the pollution of microplastic particles in the seed culture environment, our results demonstrated the reducing and balancing effects of PVC on Cd toxicity in foxtail millet seedlings, especially at low concentrations. However, this result needs more research, especially on other plants and in different concentrations of microplastics and Cd in different soils and it should not be considered as a positive effect of microplastics presence in the environment.

References:
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