The leaching of Eucalyptus hybrids and Acacia auriculiformis leaf litter: laboratory experiments on early decomposition and ecological implications in congolese tree plantations

The ®rst stage of leaf litter decomposition of two eucalyptus hybrids and Acacia auriculiformis was studied in laboratory experiments where the decaying leaves were leached with water. Although the litter of both the species were characterized by a high content of soluble compounds, little soluble organic matter of acacia litter was recovered in litter leachates. By contrast, soluble organic matter of eucalyptus litter was more resistant to degradation and was, therefore, recovered in leachates, where soluble carbon amounts and coloration varied with the age of decomposing litter. The pH of eucalyptus litter leachates decreased at the beginning of the experiment whereas the pH of acacia litter leachates increased. When added to savanna soil, litter leachates mobilized iron into soil solution, with greater effects observed from eucalyptus than from acacia. In bioassay, litter leachates were added to sand in which test plant seedlings were grown, and a strong allelopathic activity was observed with leachates from the ®rst days of eucalyptus litter decomposition. Leachates from older litter did not show any effect. The possible ecological implications of the observed processes are discussed. # 1999 Elsevier Science B.V. All rights reserved.