اثر قارچ‌هاي مايكوريزا- آربسكولار و فسفر بر جذب آرسنيك از خاك‌هاي آلوده به آرسنيت و آرسنات به‌وسيله گياه آفتابگردان

The Effects of Arbuscular-Mycorrhizal Fungi and Phosphorous on Arsenic Uptake by Sunflower Plant in Soils Spiked with Arsenite and Arsenate

در سال‌های اخیر آلودگی خاك‌ها و آب به آرسنیك به دلیل كاربردهای صنعتی و فعالیت‌های معدن‌كاری منجر به نگرانی‌های جدی زیست محیطی شده است. روش‌های مختلفی برای مدیریت زیست محیطی و پالایش خاك‌های آلوده پیشنهاد شده كه در بین این روش‌ها گیاه پالایی به عنوان گزینه‌ای موثر و سازگار با محیط زیست مطرح شده است. به منظور پی بردن به اثرات همزیستی مایكوریزایی و غلظت فسفر بر جذب آرسنیت و آرسنات بوسیله گیاه آفتابگردان، مطالعه‌ای گلخانه‌ای به صورت كاملا تصادفی در قالب فاكتوریل با سه سطح مایكوریزا (شاهد، Glomus intraradices وmosseae Glomus)، دو سطح فسفر (0 و 60 میلیگرم بر كیلوگرم) و دو گونه معدنی آرسنیك (50 میلیگرم بر كیلوگرم آرسنیت یا آرسنات) انجام شد. نتایج حاصل از آزمایش نشان داد همزیستی مایكوریزایی غلظت آرسنیك در بخش هوایی گیاه را كاهش و افزایش سطح فسفر خاك غلظت آرسنیك را در بخش هوایی گیاه آفتابگردان افزایش می‌دهد. بنابراین همزیستی مایكوریزایی بوسیله گیاه آفتابگردان بازدهی تثبیت گیاهی و افزایش غلظت فسفر در خاك بازدهی جذب گیاهی آرسنیك را در خاك‌های آلوده به آرسنیك افزایش می‌دهد.

Introduction: Arsenic is a highly toxic metalloid in group 15 of periodic table. The information on environmental behaviour of arsenic, however, is still scarce. Contamination of soils and water with arsenic and antimony due to their widespread industrial application and mining activities has raised serious environmental concerns. Nearly all Arsenic-contaminated soils results from human activities and it has different environmental and sociological impacts. Various strategies and methods have been proposed for environmental management and remediation of contaminated soils. Among all methods, the phytoremediation is receiving more attention due to its cost effective and environmental friendly characteristics. In the case of arsenic contaminated soils, there are effective factors such as soil fertility, nutrients content and microorganisms function, which can improve the uptake of As by plants. Up to now, several studies have been evaluated the effects of symbiotic fungal association in plants on increasing nutrients and toxic elements uptake. Many of authors reported that the mycorrhizal symbiosis increases the uptake of toxic elements in root and shoot of plants and consequently improve the efficacy of phytostabilization and phytoextraction processes. There are conflicting results about the effect of arbuscular- mycorrhizal fungi (AMF) on As uptake by various plants. Chen et al. (4) found that Glomus mosseae symbiosis with plant reduces As concentration and enhance phosphorus content in shoot and root of plant. Whilst Cozzolino et al. (7) reported that the AMF increases as concentration in shoot and root of cabbage. Phosphorus has important role on mycorrhizal symbiosis and also As uptake by plants. Therefore, current study was conducted to evaluated effect of Glomus intraradices and Glomus mosseae symbiosis with sunflower and also soil phosphorus concentration on uptake of arsenic from arsenite and arsenate contaminated soils. Materials and Methods:The soil sample (Typic Haplorthids) was collected, air dried and passed through 2 mm sieve and then were heated in 80 centigrade degree temperature for two times. A pot experiment was conducted in a completely randomized design with factorial arrangement and three replications in greenhouse condition. The experimental factors included two species spices of inorganic As (50 mg kg-1 of Arsenite and Arsenate), two levels of phosphorus (0 and 60 mg Kg-1) and three spices of arbuscular mycorrhizae (control, Glomus intraradices and Glomus mosseae). Soil samples spiked with Na2HAsO4.7H2O, NaAsO2 (Arsenite and Arsenate) and Ca (H2PO4)2 (phosphorus) and incubated in greenhouse condition for 4 week. Sunflower seeds were planted and seedlings harvested after 60 day of sowing and then dry weight of sunflower, concentration of As and phosphorus in shoot and root of plant and root colonization percentage determined using standard methods. Results and Discussion:The results revealed that Glomus intraradices (GI) and Glomus mosseae (GM) symbiosis significantly (P <0.05) increased the biomass production of sunflower compared with controls. There was no significant difference (P <0.05) between Arsenite and Arsenate treatments in biomass production. Also the dry weight of sunflower in Arsenite and Arsenate contaminated soil samples elevated when phosphorus concentration increased from 0 mg Kg-1(P1) to 60 mg Kg-1 soil (P2). The highest amount of biomass production observed in GI and P2 treatments that were 1.72 and 1.73 (g pot-1) in Arsenite and Arsenate contaminated soil, respectively. The results showed that the GI and GM symbiosis and phosphorus concentration significantly (P <0.05) increased phosphorus content of shoot and root of sunflower as compared to the control treatments while there was no significant difference (P <0.05) between Arsenite and Arsenate treatments. The greatest amount of phosphorus in shoot and root of sunflower achieved by GI and P2 treatments that was significantly (P <0.05) higher that control treatments but there was no significant difference (P <0.05) between GI and P2 treatments and GM and P2 treatments. The results of current study revealed that the concentration of As in root was significantly (P <0.05) higher than that in shoot of sunflower. The GI and GM symbiosis significantly (P <0.05) reduced concentration of As in root and shoot of sunflower in comparison to control treatments. The data showed that the increasing of soil phosphorus level followed by a significant (P <0.05) increase of As concentration in root and shoot of sunflower. The highest amount of As concentration in root and shoot of sunflower obtained by control and P2 treatments. Conclusion:The results of present study revealed that Glomus intraradices (GI) and Glomus mosseae (GM) symbiosis with sunflower plant can increase the phytostabilization efficacy while increasing phosphorous concentration in soils enhance plant uptake of arsenic in As contaminated soils.