کارایی کرم خاکی و ریزوباکتر‌ها بر همزیستی میکوریزایی و رشد سه گونه گیاهی در یک خاک آلوده به فلز سرب

نوع مقاله: مقاله پژوهشی

نویسندگان

1 گروه خاک شناسی، دانشکده کشاورزی، دانشگاه شهرکرد، شهرکرد،ایران

2 گروه خاکشناسی دانشگاه شهرکرد

چکیده

چکیده
سابقه و هدف: سرب از نظر سمیت و کاهش فعالیت بیولوژیکی در خاک مورد توجه است. رشد گیاهان نیز در یک خاک آلوده به فلزات سنگین به اثر متقابل بین جانداران در محیط ریزوسفر و ریشه گیاه بستگی دارد. کرم‌های خاکی، قارچ‌های میکوریزا و ریزوباکترهای محرک رشد گیاه از مهم‌ترین این ریزجانداران هستند. در این مطالعه اثر جداگانه و همزمان کرم خاکی و ریزوباکترها بر کلونیزاسیون ریشه و رشد گیاه در یک خاک آلوده مورد بررسی قرار گرفت.
مواد و روش‌ها: بذر سه گونه گیاهی شامل ذرت مرغ و گاوپونه پس از استریل سطحی و جوانه‌زنی به گلدان‌های حاوی 4 کیلوگرم خاک آلوده (جمع‌آوری شده از معدن سرب باما) و استریل شده در دمای oC 121 به مدت 2 ساعت منتقل شدند. سه گونه گیاه تلقیح شده با قارچ میکوریزا به صورت جداگانه و همزمان با کرم خاکی (Eisenia foetida) یا ریزوباکتری‌ تلقیح گردید. پس از گذشت ۳ (ذرت و مرغ) و ۴ (گاوپونه) ماه از دوره رشد تحت شرایط گلخانه، اندام هوایی گیاهان از سطح خاک جدا شدند. غلظت سرب و فسفر در خاک و گیاهان، درصد کلونیزاسیون، فراوانی اسپور و طول ریشه کلونیزه اندازه‌گیری شدند.
یافته‌ها: به‌طور‌کلی، تلقیح هر سه گیاه میکوریزایی مورد مطالعه با کرم خاکی و ریزوباکتر، درصد کلونیزاسیون ریشه، فراوانی اسپورها، قابلیت دسترسی فسفر خاک و رشد گیاه را تحت تاثیر قرار داد و بسته به نوع گیاه و موجود زنده کاملاً متفاوت بود. همبستگی بین فسفر قابل دسترس خاک و درصد کلونیزاسیون ریشه در هر سه گیاه (ذرت: 48/0-=r، 05/0P<؛ مَرغ: 74/0-=r، 001/0P< و گاوپونه: 65/0-=r، 01/0P<) منفی و معنی‌دار بود. اما همبستگی منفی بین سرب قابل دسترس و کلونیزاسیون تنها در کشت مَرغ مشاهده شد. همچنین از بین فاکتور‌های همزیستی میکوریزایی مورد مطالعه، فراوانی اسپور‌ها کمترین تغییرات را بین تیمار‌های همزمان نشان داد. از سوی دیگر، همبستگی بین فراوانی اسپور‌ها و کلونیزاسیون ریشه هر سه گیاه (غیر‌معنی‌دار در کشت ذرت؛ مَرغ: 76/0=r، 001/0P< و گاوپونه: 67/0=r، 01/0P<) نیز متفاوت بود و نشان داد که فراوانی اسپور‌ها به تنهایی شاخص مناسبی برای وابستگی میکوریزایی نیست و به نوع گیاه و موجود زنده خاک (کرم خاکی یا باکتری) بستگی دارد.
نتیجه‌گیری: نتایج این بررسی حاکی است افزایش سرب و فسفر قابل دسترس خاک می‌تواند یکی از عوامل کاهش درصد کلونیزاسیون ریشه باشد، اما اثر منفی سرب بر همزیستی میکوریزایی به حساسیت گیاه به سمیت سرب بستگی دارد. همچنین درصد کلونیزاسیون ریشه به تنهایی شاخص مناسبی از رشد گیاهان مورد مطالعه نیست و به عوامل دیگری همچون نوع گیاه، غلظت فسفر و سرب خاک بستگی دارد. همچنین هراندازه حساسیت گیاه به سمیت سرب بیشتر باشد، همبستگی بین رشد گیاه و همزیستی میکوریزایی مشهودتر است.

کلیدواژه‌ها

عنوان مقاله [English]

The efficiency of earthworms and rhizobacteria on mycorrhizal symbiosis and growth of three plant species in a soil contaminated with Lead (Pb) metal

نویسندگان [English]

  • Ali Mahohi 1
  • Fayez Raiesi 2

1 Soil Science and Engineering, Faculty of Agriculture, Shahrekord University, Shahrekord, Iran

2 Dept. of Soil Science and Engineering Faculty of Agriculture, Shahrekord University

چکیده [English]

Abstract
Introduction Lead (Pb) is considered to be particularly toxic and responsible for significant decreases in biological activities in soils. Phytoremediation is an emerging and low-cost technology that utilizes plants to remove, transform, or stabilize contaminants located in water, sediments, or soils. The success of phytoremediation depends on the interactions between rhizosphere macro and microorganisms and plant roots. Among these organisms, the role of earthworms, mycorrhizal fungi, and plant growth promoters' rhizobacteria have been considered. In this study, we have evaluated and compared the combined effects of earthworms and bacteria on root colonization and plant growth in a contaminated soil.

Material and method Three plant species seeds (Zea mays (maize); Cynodon dactylon (bermudagrass) and Stachys inflata), after surface-sterilization and germination were transplanted into each plastic pot contained 4 kg of contaminated soil (collected from bama mining area located in the southwest of Isfahan) that already autoclaved at 121 oC for 2 h. A completely randomized design with 2×2×2 factorial treatment combination was used with the following factors: with or without earthworm treatments (Eisenia foetida), with or without arbuscular mycorrhizal (AM) fungal treatments and with or without rhizobacteria. After about three (bermudagrass and maize) and four (Stachys inflata) month growth in greenhouse condition, plant shoots were harvested. Pb and phosphorus (P) concentration, root colonization, spore abundance and root colonized length were determined.
Results and Discussion In general, inoculation of these organisms differently affected root colonization, spore abundance, soil phosphorus (P) availability and plant growth, and showed variable results depending upon plant species and soil organisms involved. The significant and negative correlations between soil P availability and root colonization for all the plants (maize: r=-0.48, P<0.05; bermudagrass: r=-0.74, P
Conclusion This study showed that increasing the availability of soil P and Pb could be one of the decrease factors in root colonization, but the negative Pb effects depend on plant sensitivity. Furthermore, root colonization may not alone be a suitable index for plant growth and could be different with plant species and soil P or Pb concentrations. Furthermore, the relationship between plant growth and mycorrhizal symbiosis was higher in plant sensitive to Pb toxicity.

کلیدواژه‌ها [English]

  • AM fungi
  • Earthworms
  • rhizobacteria
  • root colonization
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