Responses of Sesamum indicum to Allelopathy of Coniferous and Broadleaved Trees

The relationships among species and the mechanics of those relationships are very complicated in mixed forests, and allelopathy is one of the most important mediators of these relationships. The types and quantities of allelopathic chemicals are different in coniferous and broadleaved trees; studying the responses of some sensitive plants, such as certain crops, to allelopathy mediated by the leaf extracts of coniferous and broadleaved trees would be an effective technique to evaluate the relationships among species in a mixed forest. In this paper, the effects of leaf extracts from Metasequoia glyptostroboides, Cedrus deodara, Liquidambar formosana, Platanus acerifolia and a mixture of of coniferous and broadleaved trees on seed germination and seedling growth of Sesamum indicum at a constant concentration (50 gDW/L) were investigated using an indoor filter paper culture dish method. The test results were evaluated using the response index (RI) and the synthesis allelopathic effect index (SE). The results showed that: (1) Four kinds of leaf extracts inhibited the germination and seedling growth of S. indicum. The order of the allelopathic inhibitory effects were as follows: L. formosana > M. glyptostroboides > C. deodara > P. acerifolia; (2) In this experiment, the single leaf extract of the coniferous species (M. glyptostroboides and C. deodara) and the single leaf extract of the broadleaved species (L. formosana and P. acerifolia) did not exhibit significant differences in the direction of the allelopathic effect on S. indicum; (3) Compared to their corresponding single leaf extracts, M. glyptostroboides + P. acerifolia and C. deodara + P. acerifolia mixed leaf extracts promoted the allelopathic effects of S. indicum, namely, the coniferous-broadleaved mixed leaf extract > one single leaf extract > another single leaf extract. The rest of the coniferous-broadleaved mixed leaf extract treatment groups neutralized the allelopathic effects of S. indicum, namely, one single leaf extract > coniferous leaf mixed extract > another single leaf extract. The conclusions could provide a scientific basis for managing forests, especially mixed forest ecosystems.