CHANGES IN SOIL PH, POLYPHENOL CONTENT AND MICROBIAL COMMUNITY MEDIATED BY EUCALYPTUS CAMALDULENSIS

Eucalyptus camaldulensis has been the main exotic species planted in reforestation programs in the tropics due to its fast growth and adaptability to climate variations. Based on the premise that the conversion from natural grazed pastures to commercial Eucalyptus plantations generates significant changes in soil properties, we assessed the impact of this exotic plantation on soil chemical and biological indicators. The study was conducted in 6 plantations across Senegal following a decreasing rainfall gradient from south to north. The plantations were divided in three lots according to their age: young plantations (established in 2003, 6 years old); intermediate plantations (established in 1998, 11 years old) and old plantations (established in 1982 and 1983, 26 years old). Our results clearly showed that E. camaldulensis plants significantly modified soil pH and soil bacterial community at all sites regardless of the age of the plantation. Microbial biomass (assessed by substrate-induced respiration), community structure (assessed by denaturing gradient gel electrophoresis profiles) and function (assessed by Catabolic Response Profile using different substrates) were all significantly decreased. The acidifying effect of E. camaldulensis, the effect of high level of polyphenols and their impact on microbial communities and ecosystem functioning were discussed.