fa اثر اسیدهیومیک و عصاره جلبک دریایی بر خصوصیات ریشه و محتوای رنگدانه‌های فتوسنتزی گیاه ذرت شیرین تحت تنش سرب و کادمیوم عمومى General پژوهشي Research <div style="text-align: justify;">&nbsp;آلودگی محیط زیست به ویژه خاک و آب، به فلزات سنگین، یکی از چالش‌های عمده جهان امروز است و از سوی دیگر گذار به سمت کشاورزی پایدار، منجر به افزایش چشمگیر علاقه به استفاده از محرک‌های زیستی شده است. از این رو به منظور بررسی اثر تنش فلزات سنگین سرب و کادمیوم و برهم‌کنش آنها با محرک‌های زیستی اسیدهیومیک و عصاره جلبک دریایی بر سیستم فتوسنتزی و خصوصیات ریشه گیاه ذرت شیرین آزمایشی به صورت فاکتوریل و در قالب طرح بلوک های کامل تصادفی در سه تکرار در شرایط کشت هیدروپونیک اجرا شد. فاکتور‌های آزمایش شامل: فاکتور اول اعمال تنش فلزات سنگین در چهار سطح (تنش صفر (شاهد)، سرب 7/5 میلی‌مولار، کادمیوم 1/31 میلی‌مولار و ترکیب سرب 7/5 میلی‌مولار + کادمیوم 1/31 میلی‌مولار با استفاده از استات سرب و کلرید کادمیوم) و فاکتور دوم شامل کاربرد محرک‌های زیستی همراه با محلول غذایی در چهار سطح (عدم کاربرد محرک زیستی (شاهد)، 120 میلی‌گرم در لیتر اسیدهیومیک، 120 میلی‌گرم در لیتر عصاره جلبک دریایی و ترکیب 120 میلی‌گرم در لیتر اسیدهیومیک + 120 میلی‌گرم در لیتر عصاره جلبک دریایی) بودند. نتایج نشان داد در شرایط تنش محتوای رنگدانه‌های فتوسنتزی (کلروفیل کل، a، b و کاروتنوئید) و خصوصیات ریشه (زیست توده تازه و خشک ریشه، طول و حجم ریشه) به&not;طور معنی‌داری کاهش یافتند. کاربرد اسید هیومیک و ترکیب اسید هیومیک + عصاره جلبک دریایی، به‌ویژه در شرایط تنش ساده سرب و تنش توأم فلزات سنگین، محتوای کلروفیل a، b و کاروتنوئید‌ها را افزایش دادند. همچنین صفات زیست توده تازه ریشه، حجم ریشه و طول ریشه با کاربرد ساده اسید هیومیک و عصاره جلبک دریایی تحت تنش فلزات سنگین عملکرد بهتری داشتند.&nbsp; درنهایت کاربرد محرک‌های زیستی موجب ارتقا شاخص‌های تحمل تنش فلز ریشه و اندام هوایی گیاهان ذرت شیرین شدند. بنابراین کاربرد محرک‌های زیستی می‌تواند یک راهکار مدیریتی و اقتصادی مؤثر در شرایط تنش فلزات سنگین باشد.<br> <br> <br> &nbsp;</div> <div style="text-align: justify;">Extended Abstract<br> Introduction: Heavy metal contamination of agricultural soils and water resources has become a major environmental concern worldwide due to rapid industrialization, urbanization, mining activities, and the excessive use of agrochemicals. Among toxic heavy metals, lead (Pb) and cadmium (Cd) are particularly hazardous because of their persistence in the environment, high mobility, and potential accumulation in plant tissues. These metals adversely affect plant growth and development by disrupting nutrient uptake, inducing oxidative stress, damaging cellular structures, and impairing photosynthetic processes. Consequently, heavy metal pollution poses a serious threat to agricultural productivity, food safety, and ecosystem sustainability. In recent years, the adoption of sustainable agricultural practices has stimulated interest in using plant biostimulants as eco-friendly tools to enhance crop resilience to abiotic stress. Humic substances and seaweed extracts are among the most widely used biostimulants due to their ability to improve nutrient availability, stimulate root development, enhance antioxidant defense mechanisms, and promote plant growth. However, information regarding their combined effects on mitigating Pb and Cd toxicity in sweet corn remains limited.<br> The present study aimed to (i) evaluate the effects of Pb and Cd stress, applied individually and in combination, on photosynthetic pigments and root growth characteristics of sweet corn plants, and (ii) investigate the potential role of humic acid and seaweed extract, applied individually and in combination, in alleviating heavy metal-induced damage and improving plant tolerance.<br> <br> Materials and Methods: The experiment was conducted under controlled hydroponic conditions using a factorial arrangement based on a randomized complete block design (RCBD) with three replications. The first factor consisted of four heavy metal treatments: control (without heavy metals), 7.5 mM Pb, 1.31 mM Cd, and a combined treatment of 7.5 mM Pb + 1.31 mM Cd. Lead and cadmium were supplied in the form of lead acetate and cadmium chloride, respectively. The second factor included four biostimulant treatments: control (without biostimulants), 120 mg L⁻&sup1; humic acid, 120 mg L⁻&sup1; seaweed extract, and a combined treatment of 120 mg L⁻&sup1; humic acid + 120 mg L⁻&sup1; seaweed extract. Biostimulants were added directly to the nutrient solution throughout the experimental period. At the end of the treatment period, several physiological and morphological parameters were measured, including chlorophyll a, chlorophyll b, total chlorophyll, carotenoid content, fresh and dry root biomass, root length, root volume, and stress tolerance indices of roots and shoots. Data were subjected to statistical analysis, and treatment means were compared at the appropriate significance level.<br> <br> Results and Discussion: Exposure to Pb and Cd significantly reduced the concentration of photosynthetic pigments compared with the control treatment. The reduction in chlorophyll and carotenoid contents indicated that heavy metals negatively affected chloroplast structure and function, thereby impairing photosynthetic efficiency. The combined Pb + Cd treatment generally produced more severe effects than individual metal treatments, suggesting additive or synergistic toxicity. Heavy metal stress also caused substantial reductions in root growth and development. Root length, root volume, and fresh and dry root biomass declined significantly under Pb and Cd exposure. These negative effects can be attributed to disruptions in cell division, membrane integrity, water uptake, and nutrient acquisition. Since roots are the primary sites of heavy metal accumulation, their growth is often among the first plant characteristics adversely affected by metal toxicity. Application of humic acid and seaweed extract significantly improved both physiological and morphological traits under heavy metal stress conditions. Plants receiving biostimulants exhibited higher chlorophyll and carotenoid concentrations than untreated plants exposed to heavy metals. These improvements may be associated with enhanced nutrient uptake, stabilization of cellular membranes, increased chlorophyll biosynthesis, and activation of antioxidant defense systems. Similarly, biostimulant treatments promoted root development by increasing root length, root volume, and biomass accumulation. Enhanced root growth likely improved the plant&#39;s ability to absorb water and nutrients while reducing the detrimental effects of heavy metal toxicity. Notably, the combined application of humic acid and seaweed extract generally yielded the greatest improvements across most measured traits, suggesting possible synergistic interactions between the two biostimulants. The calculated stress tolerance indices further confirmed the beneficial effects of biostimulant application. Both root and shoot tolerance indices increased significantly in treated plants compared with untreated stressed plants, demonstrating enhanced adaptation and resilience to heavy metal stress. These findings suggest that humic acid and seaweed extract may partially counteract the physiological and morphological damage caused by Pb and Cd contamination.<br> <br> Conclusion: The results of this study demonstrate that Pb and Cd toxicity substantially impairs photosynthetic pigment production and root development in sweet corn plants. However, the application of humic acid and seaweed extract, either individually or in combination, effectively mitigates the adverse effects of heavy metal stress by improving photosynthetic performance, stimulating root growth, and enhancing stress tolerance. The combined aplication of these biostimulants showed the greatest capacity for promoting plant resilience under contaminated conditions. Overall, humic acid and seaweed extract represent sustainable, environmentally friendly, and cost-effective management tools for reducing heavy metal stress in crop production systems. Their application may contribute to maintaining crop productivity in contaminated environments and supports the broader goal of sustainable agricultural development. Future studies should investigate the underlying physiological and molecular mechanisms involved in biostimulant-mediated heavy metal tolerance and evaluate their effectiveness under field conditions.<br> <br> <br> &nbsp;</div> تنش فلزات سنگین, شاخص تحمل تنش فلزی, محرک‌های زیستی, محتوای کلروفیل Biostimulants, Chlorophyll content, Heavy metal stress, Heavy metal stress tolerance index 99 117 http://jcpp.iut.ac.ir/browse.php?a_code=A-10-3896-1&slc_lang=fa&sid=1 Parsa Sekooti پارسا سکوتی sekooti.parsa@gmail.com No tment of Genetic and Plant Production, Faculty of Agriculture and Natural Resources گروه ژنتیک و تولیدات گیاهی، دانشکده علوم و فناوری کشاورزی، دانشگاه محقق اردبیلی، اردبیل، ایران Salim Farzaneh سلیم فرزانه salimfarzaneh@yahoo.com No Department of Genetic and Plant Production, Faculty of Agriculture and Natural Resources گروه ژنتیک و تولیدات گیاهی، دانشکده علوم و فناوری کشاورزی، دانشگاه محقق اردبیلی، اردبیل، ایران Sajjad Moharramnejad سجاد محرم نژاد s.moharramnejad@areeo.ac.ir Yes Ardabil Agricultural and Natural Resources Research and Education Center, AREEO, Moghan, Iran مرکز تحقیقات و آموزش کشاورزی و منابع طبیعی استان اردبیل، سازمان تحقیقات، آموزش و ترویج کشاورزی، مغان، ایران Raouf Seyed Sharifi رئوف سید شریفی raf.sh@gmail.com No Ardabil Agricultural and Natural Resources Research and Education Center, AREEO, Moghan, Iran گروه ژنتیک و تولیدات گیاهی، دانشکده علوم و فناوری کشاورزی، دانشگاه محقق اردبیلی، اردبیل، ایران Bahman Khoshru بهمن خوشرو bahmankhoshru@yahoo.com No 3. Soil and Water Research Institute (SWRI), Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran موسسه تحقیقات خاک و آب کشور، سازمان تحقیقات، آموزش و ترویج کشاورزی، کرج، ایران.