Document Type : Original Article
Authors
1 M.Sc. Graduate of Medicinal Plant, Department of Plant Productions, Agricultural Faculty of Bardsir, Shahid Bahonar University of Kerman, Kerman, Iran
2 Associate Professor, Department of Plant Productions, Agricultural Faculty of Bardsir, Shahid Bahonar University of Kerman, Kerman, Iran
3 Assistant Professor Department of Plant Productions, Agricultural Faculty of Bardsir, Shahid Bahonar University of Kerman, Kerman, Iran
4 , Department of Plant Productions, Agricultural Faculty of Bardsir, Shahid Bahonar University of Kerman, Kerman, Iran
Abstract
Introduction
Marigold (Calendula officinalis L.) is an annual plant in the Asteraceae family that has been cultivated for ornamental purposes for many years. However, the plant's medicinal properties have also been identified and it is now commonly used for medicinal purposes. The most abundant compounds found in marigold are phenolic compounds, including flavonoids and phenolic acids, as well as saponins. The biosynthesis of secondary metabolites in plants is heavily influenced by environmental factors, which are known to significantly affect both the quantity and composition of these compounds. Environmental factors can be present in varying conditions, sometimes in levels that are optimal for plant growth and sometimes in levels that are stressful and can negatively impact plant growth and development. A substantial portion of the earth's arable land, approximately 6%, is affected by salinity, which can lead to oxidative stress in plants. Although, zinc is an essential micronutrient required for plant growth, excessive levels of this element can be toxic and result in oxidative stress, ultimately leading to plant death. There are various methods to mitigate the impacts of metal toxicity and salinity stress on plants, and one effective approach is the use of biochar as a soil amendment. Beeswax waste has recently been identified as an organic material, and studies have shown that it is a nutrient-rich substance that can be applied as a fertilizer. Given the dual importance of marigold as both a medicinal and ornamental plant, the present study aimed to explore the potential of beeswax waste biochar in mitigating the negative impact of salinity and zinc stress on this plant species. Furthermore, the study aimed to investigate the effects of varying concentrations of zinc, ranging from low to high levels, on the growth and development of marigold. The study also examined the synergistic effects of zinc and salinity on marigold growth, as well as the role of both high and low concentrations of zinc under saline conditions and in the presence of different biochar levels.
Materials and methods
To investigate the impact of beeswax waste biochar application on marigold growth under salinity and zinc stress, a factorial experiment was conducted using a completely randomized design with three replications. The experimental factors included two levels of salinity stress (control EC=1 dsm -1; salt stress with EC=6 dsm-1), four levels of zinc element (control, 300, 1500, and 3000 mgkg-1 soil), and three levels of beeswax waste biochar (control, 1.5%, and 3% ww-1). Biochemical traits, including photosynthetic pigments (chlorophyll a, b, and total), phenol, flavonoid, anthocyanin, catalase, and ascorbate peroxidase enzymes, were measured three months after planting. Yield traits, such as biomass and flower dry weight, were measured approximately four months after planting, when the plants exhibited signs of decline.
Results and discussion
The results of the experiment revealed that salinity and zinc stress significantly reduced the biomass, flower and root dry weight, and height of marigold plants compared to the non-stress condition. Among the treatments, the highest amount of biomass and dry weight of flowers were observed in the control treatment (without salinity stress) with 300 ppm of zinc and 1.5% biochar, which were 9.83 gr and 1.59 gr, respectively. Conversely, the lowest values were observed in the treatment with 6 dSm-1 salinity and 1500 ppm of zinc concentration without biochar, which were 1.8 gr and 0.27 gr, respectively. Although the amount of photosynthetic pigments and secondary metabolites, such as phenolic compounds, flavonoids, and anthocyanins, decreased compared to the non-stress condition, the activity of catalase and ascorbate peroxidase enzymes increased under salinity and zinc stress compared to the control treatment. Furthermore, the application of biochar in plants under salinity and zinc stress conditions increased vegetative traits, improved photosynthetic pigments, secondary metabolites, and antioxidant enzymes compared to the condition of not applying biochar.
Conclusion
Low zinc concentration had a positive impact on marigold growth, but concentrations higher than 300 ppm resulted in toxicity and stress. Salinity and zinc stress caused a decrease in growth characteristics, photosynthetic pigments, and secondary metabolites. Remarkably, the application of biochar, even in the presence of salt stress with 300 ppm zinc concentration, improved the growth and biochemical characteristics of marigolds.
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