Allelopathic hypotheses revisited: the interactions between native and exotic species in the Brazilian savanna.

We investigated allelopathic interactions between native and exotic species of the Cerrado biome. We studied the effects of the exotic Andropogon gayanus and the native A. bicornis on the initial growth of two native (A. fastigiatus and Lepidaploa aurea) and two exotic species (Melinis minutiflora and Stapfochloa elata). Leaves or roots of the donors were each mixed at ratios of 0.75, 1.5 and 3% (litter/soil) with soil samples collected in the same areas where they spontaneously co-occur with their target species. We found that A. gayanus inhibited the growth of all target species, what agrees with the novel weapon hypothesis. The native A. bicornis stimulated the growth of the two native species and of S. elata but inhibited the growth of the exotic M. minutiflora, in line with the homeland security hypothesis. Our studies suggest that allelopathy may have a part in the invasiveness of A. gayanus and that the inhibitory effect of A. bicornis on the growth of M. minutiflora might help to control the spread of this exotic grass. We conclude that allelopathy may be involved in the interactions between species and be used in controlling the spread of exotic species over many areas of the Cerrado.