Research On Allelopathic Effects Of Extracts From A. Philoxeroides On Three Kinds Of Crops

Allelopathy is the phenomenon that plants and microorganisms release chemical substances to surroundings by secretion, volatilization, rain eluviation or residues decomposition, and the growth of other plants and microorganisms are inhibited or improved. Allelopathy can be widely used in biological control, plant protection, forest tending and yield promotion and so on.Alternanthera philoxeroides Griseb, commonly known as alligator weed, is classified as Amaranthaceae family, Alternanthera genus, its growth is very rapid because of its strong vitality in aquatic and terrestrial environment, it is a malignant invasive plant that has spread throughout our country. A. philoxeroides can propagate asexually with rhizome, it can grow under certain conditions even only with a small section of stem or root. Its stolon is well developed and new roots can grow out from the node and finally new plant is formed. So it can spread around in a short period of time to form a large single community, and is very harm to the environment, the agricultural economy and biodiversity of our country. It is listed in the first directory of invasive species by the State Environmental Protection Administration in2003. So it is important to study the allelopathy of A. philoxeroides, and is helpful for further illustrating the mechanism of invasion and effective management of invasive species. In this study, the aqueous solutions were extracted respectively from upground, underground, upwater and underwater parts of A. philoxeroides, and the allelopathic effects of aqueous extracts on seed germination, seedling growth and physiology was investigated in rice (Oryza sativa), maize(Zea mays L.) and rape (Brassica napus L). The results showed that the extracts of A. philoxeroides could observably inhibit the seed germination rate and germination potential of rice, maize and rape seeds. Under low concentration of extracts (less than0.05g/mL), the root growth of receptor seedlings was improved while under high concentration was inhibited., the higher of concentration, the more was inhibited. Under the treatment of different extracts from A. philoxeroides, the activities of peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT) in seedlings of3crops decreased, while the malondialdehyde (MDA) content increased. The results indicated that extracts of A. philoxeroides could increase the active oxygen content in receptor’s cells, and then the functions of macro molecules were damaged, leading to the lipid peroxidation of membrane, Consequently the product of lipid peroxidation MDA was produced, and antioxidant enzyme system was also damaged in a certain degree. In addition, the leakage of electrolytes in leaf cells was higher than control, which indicated that the membrane in leaf cells of receptors was damaged, so the leakage of electrolytes increased. Under high concentrations of extracts, the chlorophyll content, chlorophyll characters such as Fm, Fv/Fo, Fv/Fm, qP and NPQ decreased, while Fo increased. This indicated that the PSII reaction center in receptors was inhibited and photosynthetic electronic transfer was also hampered, so the photosynthesis in receptos was influenced by the allelochemicals in extracts of A. philoxeroides. As for the extracts of different concentrations and different parts, the allelopathic effects of extracts from underground parts were higher than that from upground parts, and underwater parts higher than upwater parts. The allelopathic effects and concentrations of extracts were positively related, that is, the higher the extract concentration, the stronger the allelopathic effects. Additionally, different receptor crops had different allelopathic sensitivities to extracts of A. philoxeroides, which changed as rape> corn> rice.Based on the research, the results showed that there was strong allelopathic effects in A. philoxeroides, and the extracts of A. philoxeroides could affect the seed germination, root growth, leaf membrane leakage and the activities of enzyme in rice, maize and rape. So it could be concluded that releasing allelopathic chemicals to the environment might be one of the main factors for A. philoxeroides to successfully invade into new ecosystem.