Document Type : Research Article
Authors
1
Department of Environmental Sciences, Gorgan University of Agricultural Sciences and Natural Resources
2
Ferdowsi University of Mashhad
3
Department, of Environmental Science ,Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran
Abstract
Introduction
Invasive alien plants pose significant ecological and socio-economic threats due to their aggressive spread and disruption of native ecosystems. One mechanism aiding their success is allelopathy—the release of biochemicals (allelochemicals) that inhibit the germination and growth of nearby native species. While the phenomenon is well-documented, its exact role in biological invasions remains underexplored. Recent studies reveal that approximately 72% of plant families, including many invasive species, possess allelopathic capabilities, challenging the earlier notion that it is restricted to a few plant lineages (Kalisz er al., 2021).
Senecio angulatus, commonly known as Cape ivy or creeping groundsel, is a fast-growing, perennial vine native to South Africa. It has become an invasive species in several parts of the world including Europe, Australia, and Northern Africa (GBIF, 2023). It has recently been observed in the Golestan Province of Iran, particularly in the coastal areas of Bandar-e-Gaz (Sohrabi et al., 2025). Several studies have been identified the alleloapthic potential of invasive plants of Asteraceae family (Silva et al., 2014; Perera et al., 2023). In order to investigate its allelopathic potential as an invasive and important plant in different parts of the world, the emergence and early growth of five native plant species were considered in stem and leaf debris of Senecio angulatus.
Research Objective
This study aimed to evaluate the allelopathic potential of S. angulatus through its decomposed above-ground biomass in soil, and its subsequent effect on the germination and growth of native and indicator plant species.
Materials and Methods
The experiment was conducted in a greenhouse using a completely randomized design with four replications. Leaves and stems of S. angulatus collected from Gorgan were mixed with agricultural soil at 1:5 ratio and incubated for either 2 or 8 months to allow decomposition. The treated (contaminated) soil and control (uncontaminated) soil were used to grow five plant species: lettuce (Lactuca sativa), alfalfa (Medicago sativa), purslane (Portulaca oleracea), chicory (Cichorium intybus), and maize (Zea mays). Lettuce and maize considered as indicator species.
Seeds were sown in pots containing the treated or control soil. Germination rate, root and shoot length, and dry biomass were recorded after four weeks. The Response Index (RI) was used to compare the response of the species in the contaminated soil for which the inhibitory effect ranged from +1 to -1, where values close to -1 indicate strong inhibition.
Results and Disscussion
• Emergence: The inhibitory effects were more pronounced after 8 months of soil incubation. Lettuce showed the most significant reduction in emergence, followed by purslane and chicory. Maize was least affected, possibly due to its larger seed size and stronger initial growth.
• Root Length: Although not consistently significant, the most notable reductions in root length occurred in lettuce and chicory after 8 months.
• Shoot Growth: Significant inhibitory effects on shoot length were recorded, especially for lettuce and purslane. In contrast, alfalfa, chicory, and maize exhibited varying degrees of resistance depending on the timing.
• Root and Shoot Biomass: Lettuce consistently showed the highest reduction in biomass, while maize showed the lowest. Chicory and purslane also showed considerable sensitivity.
• Overall RI Analysis: Lettuce exhibited the strongest allelopathic response, followed by purslane and chicory. Maize displayed the least sensitivity, suggesting its higher tolerance.
The response varied between species and time of sowing, with the greatest reduction in emergence observed when seeds were sown after eight months of mixing the soil. In addition, the lowest response index (most inhibitory effect) was observed in the dry weight roots and stems of five species. A comparison of the species' responses to the inhibitory effect of the contaminated soil showed that alfalfa and maize were less affected (-0.21 and -0.03, respectively), while chicory, purslane and lettuce were more affected (-0.31, -0.36 and -0.61, respectively).
Recent studies, including preliminary phytochemical analyses, have confirmed the presence of potent allelochemicals such as total phenols, flavonoids, chlorogenic acid, and cynarin in S. angulatus. These compounds are known for their allelopathic and antioxidant activities. The plant, being a member of the Asteraceae family, is also capable of producing pyrrolizidine alkaloids, known for their ecological toxicity.
Several related species in the Asteraceae family (e.g., Solidago gigantea, Artemisia baimaensis, Senecio jacobaea) have shown similar allelopathic effects, reinforcing the hypothesis that S. angulatus may exert strong inhibitory influence on native flora through both chemical and microbial soil interactions.
Implications and Recommendations
• Maize and other large-seeded or resilient species may serve as better alternatives in areas threatened by this invader.
• It is essential to manage and prevent the further spread of S. angulatus, especially in ecologically sensitive coastal regions.
• Removing plant residues and controlling its ornamental use are practical steps for early-stage management.
• Further studies on soil microbial changes and identification of specific allelochemicals are recommended for comprehensive ecological assessments.
Conclusion
The findings affirm that Senecio angulatus possesses significant allelopathic capabilities, capable of suppressing native plant growth through soil contamination. The consistent inhibitory effects on native and indicator species suggest a high allelopathic potential in S. angulatus, reinforcing its invasive risk. The implementing management programs to monitor the cultivation of the plant at national level and eradicate established populations is considered to be particularly necessary in the northern parts of Iran.
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