Phytotoxic effects of invasive Ageratina adenophora on two native subtropical shrubs in Nepal

The response of native plants to allelopathic interference of invasive species may differ from species to species. In this study, the phytotoxic effects of Ageratina adenophora were tested on two native shrubs (Osbeckia stellata and Elsholtzia blanda) of Nepal. Both the shrubs were grown in pots under treatments of A. adenophora fresh leaves and root leachates, and litter. Then, the seedling length and biomass were compared among the treatments. The results show that A. adenophora litter has stimulatory effects but the leachates from fresh leaves and root are phytotoxic to the growth and development of native shrubs. Infrared Spectroscopy (IR) analysis confirmed the presence of O–H (Hydroxyl), N–H (Amines), C≡C (Alkynes), and C–H stretching (Aromatic) or C–O–C stretching (Ethers) in the leachates representing harmful allelochemicals. The invaded soil by A. adenophora had low pH and a high amount of organic matter, total nitrogen, phosphorus, and potassium than the uninvaded soil. The results indicate that the native O. stellata and E. blanda are harmed by A. adenophora in nature by leaching of allelochemicals and probably by reducing the soil pH. Overall, this study has provided valuable insights regarding the effects of A. adenophora invasion on native shrubs and revealing the potential mechanism of its invasiveness.

Phytotoxic evaluation of Phragmites australis: an investigation of aqueous extracts of different organs

Phragmites australis is one of the most widespread and invasive plants on earth. Allelopathic interference has been considered as a possible way associated with its invasiveness in wetlands. A series of ecologically realistic experiments was conducted to explore allelochemical phytotoxicity of Phragmites. Germination bioassays using aqueous extracts of different organs (leaf, stem, root and rhizome) of Phragmites were tested with model seeds (Lactuca sativa and Raphanus sativus) and associated plant species (Juncus pallidus and Rumex conglomeratus). These studies showed that leaf and rhizome extracts exhibited strong inhibition on germination, biometric and physiological parameters (all P ≤ 0.001). Dose–response studies confirmed LC50 (4.68% and 11.25%) of Lactuca for leaf and rhizome extracts respectively. Root growth of Juncus and Rumex was inhibited by 75% and 30%, respectively, in leaf leachate-incorporated soil. Chlorophyll content and maximum quantum yield (Fv/Fm) were significantly reduced with leaf and rhizome leachates. The stability and quantity of water-soluble phenolics in anaerobic versus aerobic condition may influence phytotoxic effects to other species. Phragmites organs can be ranked in order of allelopathic potentiality as follows: leaf > rhizome > root > stem. The present study highlighted the potential impacts of allelochemicals on plant recruitment in wetlands invaded by Phragmites.