Allelopathy and invasiveness of Bidens pilosa and Mimosa pudica.
This research aimed to determine the allelopathic effect of the invasion mechanism of the exotic plants Bidens pilosa and Mimosa pudica. The effects of extracts from the roots, stems and leaves of both B. pilosa and M. pudica on seed germination and seedling growth (root length, stem length and root:shoot ratio) were studied using a petri dish filter paper method. It was found that: (1) B. pilosa extracts had a large concentration dependent effect on the seed germination of both B. pilosa and M. pudica, with leaf extracts being the most potent (67%-87% germination inhibition at the highest tested concentration). M. pudica leaf extracts at high concentration reduced germination of their own seeds by 21.7% but had no significant effect on germination of B. pilosa seeds. (2) Root, stem and leaf extracts (but especially leaf extracts) of both species all induced a concentration dependent reduction in root length of their own seedlings and of the other species. (3) Root, stem and leaf extracts of B. pilosa strongly reduced stem length of M. pudica at all tested concentrations. Only stem and leaf extracts of M. pudica at high concentrations showed any allelopathic effect on stem length of B. pilosa. Root and leaf extracts of M. pudica at medium concentrations enhanced stem growth of B. pilosa. M. pudica extracts had a moderate, concentration dependent autotoxicity effect on their own seedling stem length. For B. pilosa, only leaf extracts at high concentration reduced stem length of their own seedlings. (4) B. pilosa extracts (especially leaf extract) induced a strong concentration dependent reduction of root:shoot ratio of their own seedlings while all three extracts enhanced root:shoot ratio of M. pudica seedlings. M. pudica extracts caused only a mild reduction in root:shoot ratio of their own seedings, but a substantial reduction in root:shoot ratio of B. pilosa seedlings. (5) An index of allelopathic or autotoxicity intensity was calculated from the data. Autotoxicity intensity of B. pilosa on its own seed germination rate, root length and root-shoot ratio was greater than that of M. pudica, while the allelopathy intensity of B. pilosa on the stem length of M. pudica was greater than that of M. pudica on B. pilosa, and was also greater than its autotoxicity intensity. The intensity of allelopathic effects of M. pudica on the root length and root:shoot ratio of B. pilosa was greater than the self-inhibition of B. pilosa, and was greater than its self-toxicity intensity. B. pilosa mainly inhibited the stem length of M. pudica to enhance its invasiveness, while M. pudica mainly inhibited the growth of B. pilosa roots to increase its competitiveness.