Journal of Chemical Ecology, Vol. 20, No. 11, 1994 COMPARATIVE ANALYSIS OF ALLELOPATHIC EFFECTS PRODUCED BY FOUR FORESTRY SPECIES DURING DECOMPOSITION PROCESS IN THEIR SOILS IN GALICIA (NW SPAIN) X.C. SOUTO, t L. GONZALEZ, 2 and M.J. REIGOSA 2'* tDepartrnento de Recursos Naturais e Medio Ambiente Area de Produccidn Vexetal E. U. L 7". de lndustrias Forestais Universidade de I/igo Apdo. 874. 36200 Vigo, Spain 2Departarnento de Recursos Naturais e Medio Ambiente Area de Bioloxia I/exetal Facultade de Ciencias, Universidade de Vigo Apdo. 874. 36200 Vigo, Spain (Received May 12, 1994; accepted July 11, 1994) Abstract--The development of toxicity produced by vegetable litter of four forest species (Quercus robur L., Pinus radiata D.Don., Eucalyptus globulus Labill, and Acacia melanoxylon R.Br.) was studied during the decomposition process in each of the soils where the species were found. The toxicity of the extracts was measured by the effects produced on germination and growth of Lactuca sativa L. var. Great Lakes seeds. The phenolic composition of the leaves of the four species was also studied using high-performance liquid chromatographic analysis (HPLC). It was verified that toxicity was clearly reflected in the first stages of leaf decomposition in E. globulus and A. melan- oxy.lon, due to phytotoxic compounds liberated by their litter. At the end of half a year of decomposition, inhibition due to the vegetable material was not observed, but the soils associated with these two species appeared to be responsible for the toxic effects. On the other hand, the phenolic profiles are quite different among the four species, and greater complexity in the two toxic species (E. globulus and A. melanoxylon) was observed. Key Words--Allelopathy, decomposition, litter, Quercus robur L., Pinus radiata D.Don., Eucalyptus globulus Labill, Acacia melanoxylon R.Br., phe- nolics. *To whom correspondence should be addressed. 3005 009S-033i 19411100-3005507.00/0 91994PlenumPublishing Corporation