Allelopathic potential of two aquatic plants, duckweed (Lemna minor L.) and water lettuce (Pistia stratiotes L.), on terrestrial plant species

The allelopathic potential of two aquatic species, duckweed (Lemna minor L.) and water lettuce (Pistia stratiotes L) was examined on the seedling growth of eight test terrestrial species, alfalfa (Medicago sativa L), cress (garden cress, Lepidium sativum L), lettuce (Lactuca sativa L), barnyard grass (Echinochloa crus-galli (L). Beauv.), crab grass (Digitaria sanguinalis L), junglerice (Echinochloa colonum (L) Link.), rye grass (Lolium multiforum L) and timothy (Phleum pratense L), and on the germination of cress and barnyard grass. Aqueous methanol extracts of the two aquatic species inhibited root growth of all test species at >= 0.01 g dry weight equivalent extract mL(-1) (g DW eq. extract mL(-1)) and shoot growth at >= 0.03g DW eq. extract mL(-1). Although the inhibitory effects of the two aqueous methanol extracts on test species varied and were non-selective, an irreversible dose-threshold (1 g DW eq. extract mL(-1)) was necessary to completely inhibit the seedling growth and germination of all test species. These results suggest that duckweed and water lettuce may contain allelochemicals which are inhibitory to the growth and germination of terrestrial plant species. (C) 2012 Elsevier B.V. All rights reserved.