Allelopathic effects of exotic tree species on microorganisms and plants in Galicia (Spain)

During one year, the evolution of eleven groups of micro-organisms has been monitored in the soil in a plantation of oakwood (Quercus robur, the autoc hthonous tree species) and three alien trees (Acacia melanoxylon, Eucalyptu s globulus and Pinus radiata). The main differences could be attributed to the different water regimes and soil pH, but also to some extent to the all elochemicals released. Also, the effect of the litter decomposing in the so ils on germination and seedling growth was studied. The results are compati ble with Rabotnov's hypothesis, that is, that allelopathy is mainly possibl e between plants that have not coevolved or in special conditions where phy totoxins are accumulated. The results are discussed regarding to this hypot hesis.