Allelopathy of floodplain vegetation species in the middlecourse of the Tama River [Japan]

Summary We evaluated allelopathic activity of leaves of floodplain vegetation species collected from the floodplain of the middlecourse of the Tama River, where the invasion of alien plants and decline of floodplain endemic plants are remarkable, by the sandwich method using lettuce (Lactuca sativa L., Great Lakes 366) as the receptor plant. Dominant aliens in the floodplain, such as Robinia pseudoacacia L., Sicyos angulatus L. and Ambrosia trifida L., and dominant endemics such as Pueraria lobata (Willd.) Ohwi, Salix integra Thunb. and Miscanthus sinensis An-derss. exhibited strong activity. We sand-cultured Aster kantoensis Kitam., an endangered floodplain endemic plant, and 10 species distributed characteristically around A. kantoensis for 1.5 to 2 months after seeding. Then we evaluated the allelopathic activity of these plants by the sandwich method for leaf activity, and the plantbox method for root activity. All alien plants around A. kantoensis except Erigeron canadensis L. displayed strong activity in both leaves and roots. These results indicate the probability that the allelopathy of dominant alien plants is involved in their invasion and domination. As leaves and roots of A. kantoensis also exhibited strong activity, the soil sickness that is often observed in A. kantoensis populations over 10 years old might be due to its allelopathic effect. Leaves of other floodplain endemics such as Artemisia capillaries Thunb. and Potentilla nipponica Th. Wolf collected from the Tama River, didn't displayed strong activity. Allelopathic activities of floodplain vegetation species of the Tama River could vary with specific conditions as high soil pH, as well as growth stages of plants. It is quite important to clarify the effect of those elements against allelopathic activity as well as the relationship between succession and allelopathy in floodplain vegetation.