Allelopathic effects of invasive Acacia mangium on germination and growth of local paddy varieties

Abstract

Laboratory and plant house experiments were conducted to study the allelopathic effects of Acacia mangium (Fabaceae), an invasive plant species in Brunei Darussalam, on germination and growth of two local paddy varieties. Germination, relative growth rates and/or biomass allocations of paddy Laila and Pusu were determined using a series of aqueous leaf extract concentrations and aqueous soil extract concentrations from A. mangium plantation and heath forest. Laila appears to be the most sensitive target species as its germination and relative growth rates based on elongations lengths (RERs) were affected by all the three types of extracts. Mean percentages germination of seeds treated with A. mangium leaf and A. mangium and heath forest soil extracts significantly decreased in Laila and Pusu as extract concentration increased to 10/12%. Mean RERs of seeds treated with 12% of A. mangium leaf extract were significantly slower in both Laila and Pusu as compared to the control. Both types of soil extracts significantly decreased RERs in Laila but not Pusu. At 5% of leaf extract concentration, Laila seedlings allocated a higher proportion of dry mass to roots but a lower proportion of dry mass to shoots (or a higher root-to-shoot ratio) than in other treatments but this differential allocation did not translate into greater final total dry biomass or faster growth rates. Acacia mangium negatively affected germination and growth of paddy. It is suggested that careful planning needs to be undertaken before using invasive species in any integrated land use systems.