Allelopathic effects of exotic mangrove species Laguncularia racemosa on three native mangrove species in China

To assess the allelopathic potential of exotic mangrove species Laguncularia racemosa (L.) Gaertn. F. (Combretaceae) on 3-native mangrove species: Avicennia marina (Forsk.), Aegiceras corniculatum (L.) Blanco and Kandelia obovata (L.) Druce seedlings, 5-concentrations (0.1, 0.2, 0.3, 0.4, and 0.5 g·mL-1) of root aqueous extracts were studied. The results showed that high concentrations (0.5 g·mL-1) of L. racemosa root extract significantly inhibited the seedling growth and total chlorophyll content in leaves of A. corniculatum. In contrast, seedling growth and chlorophyll content in leaves of the A. marina and K. obovata were stimulated at lower concentrations (0.1 and 0.2 g·mL-1), but were significantly inhibited at higher concentrations (0.3, 0.4 and 0.5 g·mL-1). The allelopathic effects from aqueous extract of L. racemosa roots followed the trend: A. corniculatum >A. marina > K. obovata. To identify the allelochemicals in root extracts, the N-butanol extract of L. racemosa roots aqueous extract was analyzed by GC-MS. Total of 27 compounds were found, including 2 amines (5.95%), 1 acid (0.54%), 2 ketones (14.79%), 11 esters (29.62%), 4 alcohols (3.09%), 1 pyrazole (1.51%), 2 phenols (3.53%), 1 quinone (1.81%), 2 alkanes (1.88%), 1 benzene (1.88%). Further field experiments are needed to investigate the variability of inhibitory and stimulatory effects of L. racemosa root extract on native mangrove species in China.