Allelopathic potential ofAnthoxanthum odoratum for invadingZoysia-grassland in Japan

The growth ofZoysia japonica surroundingAnthoxanthum odoratum onZoysia-grassland in Japan was investigated in June 1994. The stem density ofZ. japonica tended to decrease with short distances between twoA. odoratum plants. This showed that the growth ofZ. japonica surroundingA. odoratum was reduced. Basic, neutral, and acidic fractions extracted fromA. odoratum plants inhibited the seedling growth of lettuce. In particular the neutral fraction showed the strongest activity among the three fractions. The main inhibitory compound obtained atR f 0.6-0.7, on the thin-layer chromatogram of the neutral fraction, was isolated and identified as coumarin by means of GC-MS. Coumarin solution inhibited seedling growth ofZ. japonica in low concentrations but, conversely, promoted seedling growth ofA. odoratum. Coumarin was contained in all parts ofA. odoratum and its concentration varied with the season and from one individual plant to another. In particular, coumarin was highly concentrated in the leaves, accounting for more than 2.5% of dry leaf weight in June. The inhibitory effect of these aqueous extracts was correlated to the amount of coumarin inA. odoratum leaves and cournarin was considered to be the main inhibitory compound.