تاثیر کاربرد کیتوسان بر جمعیت برخی گروه های میکروبی و شناسه های اکوفیزیولوژیک در یک خاک آلوده به سرب

نوع مقاله : مقاله کامل علمی پژوهشی

نویسندگان

1 دانش آموخته کارشناسی‌ارشد گروه مهندسی علوم خاک

2 علوم و مهندسی خاک، دانشکده کشاورزی، دانشگاه زنجان، زنجان

3 استادیار گروه شیمی، دانشگاه زنجان

10.22069/ejsms.2022.19336.2035

چکیده

سابقه و هدف: آلودگی خاک‌های کشاورزی به فلزهای سنگین یکی از چالش‌های مهم در سراسر جهان است. جامعۀ زندۀ خاک و به دنبال آن فرآیندهایی که توسط این ریزجانداران کنترل می‌شود، از تنش فلزهای سنگین متاثر می‌شوند. هدف از این پژوهش ارزیابی تأثیر کاربرد سطوح کیتوسان و آلودگی خاک به سرب بر فعالیت زیستی خاک بود.
مواد و روش‌ها: به منظور بررسی اثرات سطوح مختلف سرب (بدون آلودگی (Pb0)، 250 (Pb250) و 500 (Pb500) میلی‌گرم بر کیلوگرم خاک) و کیتوسان (بدون کاربرد کیتوسان (Ch0)، 6/0 % (Ch0.6) و 2/1 % (Ch1.2)) بر غلظت سرب قابل جذب (سرب قابل استخراج با DTPA) و برخی ویژگی‌های زیستی خاک آزمایشی به صورت فاکتوریل در قالب طرح پایه کاملا تصادفی انجام شد. در ظروف پلاستیکی سطوح مختلف سرب و کیتوسان به400 گرم خاک در سه تکرار افزوده شد و خاک‌ها در رطوبت70% ظرفیت زراعی به مدت 45 روز خوابانده شدند. پس از پایان دوره خوابانیدن افزون بر تعیین غلظت سرب قابل استخراج با DTPA، جمعیت گروه‌های میکروبی مانند باکتری‌های هتروتروف، قارچ‌ها، باکتری‌های سازنده اسپور و اکتینومیست‌ها تعیین شد و کربن و نیتروژن زیتوده میکروبی، تنفس پایه و تنفس برانگیخته برآورد گردید. همین‌طور برخی شناسه‌های اکوفیزیولوژیک شامل ضریب متابولیک (qCO2)، ضریب تنفس میکروبی (QR) و نسبت کربن به نیتروژن زیتوده میکروبی MBC:MBN)) بررسی شد.
یافته‌ها: کاربرد تیمار Pb250 اثر معنی‌داری بر جمعیت گروه‌های میکروبی بررسی شده در مقایسه با شاهد نشان نداد. کاربرد تیمار Pb500 بطور معنی‌داری سبب کاهش جمعیت اکتینومیست‌ها و جمعیت باکتری‌های سازنده اسپور گردید ولی اثر معنی‌داری بر نسبت جمعیت قارچ به باکتری نداشت (p ≤ 0.05). تنفس پایه و برانگیخته، کربن و نیتروژن زیتوده میکروبی در تیمار Pb500 بطور معنی-داری کاهش یافت. تیمار Pb500 ضریب متابولیک، ضریب تنفس میکروبی و نسبت MBC:MBN را افزایش داد. کاربرد کیتوسان در هر دو سطح سبب کاهش غلظت سرب قابل جذب در خاک گردید بطوریکه کاربرد تیمار 2/1 % کیتوسان زیست ‌فرآهمی سرب را به میزان 42% در تیمار Pb250 و به میزان 12% در تیمار Pb500 کاهش داد. کاربرد کیتوسان تنفس پایه را بویژه در تیمار Pb500 افزایش داد و سبب کاهش qCO2 گردید (p ≤ 0.05).
نتیجه‌گیری: می‌توان گفت که کاربرد کیتوسان در سطوح پایین آلودگی از نظر کاهش درصد زیست فرآهمی سرب کارآمدتر بود. همچنین به نظر می‌رسد بخشی از آثار مثبت کاربرد این پلیمر زیستی بر ویژگی‌های زیستی خاک ناشی از تجزیه زیستی آن در خاک مورد مطالعه بوده ‌است. بطور کلی نتایج نشان دهنده اهمیت کاربرد کیتوسان به عنوان یک جاذب زیست تجزیه‌پذیر برای کاهش غلظت سرب قابل جذب در خاک و پتانسیل آن برای تقویت فعالیت زیستی در خاک آلوده به سرب می‌باشد.

کلیدواژه‌ها


عنوان مقاله [English]

The effect of chitosan application on some microbial population and eco-physiological indices in a Pb contaminated soil

نویسندگان [English]

  • Niloofar Hassani 1
  • Setareh Amanifar 2
  • Mahnaz Esteki 3
1 M.Sc. Graduate, Dept. of Soil Science, University of Zanjan
2 Dept. of Soil Science, Faculty of Agriculture, University of Zanjan, Zanjan , Iran
3 Assistant. Prof., Dept. of Chemistry, University of Zanjan
چکیده [English]

Background and objectives: Contamination of agricultural soils with heavy metals is one of the major challenges worldwide. Heavy metal stress can affect soil living community and, consequently, different soil processes. The aim of this study was to evaluate the effect of chitosan application levels and soil contamination with Pb on soil biological activity.
Materials and methods: In order to investigate the effects of different levels of Pb (non-contaminated (Pb0), 250 (Pb250) and 500 (Pb500) mg kg-1 of soil) and chitosan application (without chitosan (Ch0), 0.6% (Ch0.6) and 1.2 % (Ch1.2)) on the available Pb (DTPA-extractable Pb) and some biological properties in soil, a factorial experiment was conducted in a completely randomized design. Different levels of lead and chitosan were added in pots containing 400 g of soil in three replications and and soil moisture was maintained at 70% field capacity for 45 days. At the end of the incubation period, DTPA-extractable Pb and the population of microbial groups including heterotrophic bacteria, fungi, spore-forming bacteria and actinomycetes were determined. Moreover, microbial biomass of C (MBC) and N (MBN), basal respiration (BR) and substrate-induced respiration (SIR) were measured and some ecophysiological characteristics including microbial metabolic quotient (qCO2), microbial respiration quotient (QR) and MBC: MBN ratio were calculated.
Results: The results showed that Pb250 treatment did not show a significant effect on the population of the studied microbial groups compared to the control. Application of Pb500 treatment significantly reduced the population of spore-forming bacteria and actinomycetes but did not lead to a significant change in the faungi/bacteria ratio. BR, SIR, MBC and MBN were significantly reduced by Pb500 treatment. Under Pb500 treatment, qCO2, QR and MBC:MBN ratio increased. Application of chitosan at both levels decreased the available Pb concentration of lead in the soil so that application of 1.2% chitosan reduced DTPA-extractable Pb by 42% in Pb250 treatment and by 12% in Pb500 treatment. Application of chitosan increased BR, especially under Pb500 treatment, and caused a decrease in qCO2 (p ≤ 0.05).
Conclusion: It can be stated that the use of chitosan at low levels of soil pollution was more effective in reducing the Pb bioavailability. It also seems that the positive effects of the application of this biopolymer on the biological properties of the soil have been partly due to its biodegradation in the studied soil. In general, the results indicate the importance of chitosan application as a biodegradable adsorbent to reduce available Pb in soil and its potential to enhance biological activity in Pb-contaminated soil.

کلیدواژه‌ها [English]

  • Biopolymer
  • Heavy metals
  • Microbial community structure
  • Carbon to nitrogen ratio of microbial biomass
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