Effects of Jatopha curcas L. plantation on soil bacterial and fungal communities

The use of Jatropha curcas L. (Jatropha) as agrofuel is currently increasing in tropical and sub-tropical regions. This plant and other Jatropha species are well known for synthetising various toxicants. However, the effects of Jatropha plantation on soil microbiota have barely been investigated. We sampled three sites planted with Jatropha for 1, 2 and 15 years in Senegal, together with their adjacent fallow plots, to test whether Jatropha could have detrimental effects on microbial activity and diversity. We further hypothetised that the extent of the effects of Jatropha would be correlated to plantation age. We observed that the genetic structure of the fungal community, and especially its Glomeromycota component, was strongly affected by Jatropha in all sites. The composition of the total bacterial community, especially of the nitrogen-fixing community, was also impacted but only in 2 sites out of 3. Besides, in situ catabolic potentials shifted similarly in response to Jatropha growth. Despite these microbial shifts, we cannot conclude to a negative impact as diversity indices (catabolic potentials, genetic profiles) were not lowered. Additionally, no cumulative effect was evidenced between the youngest and the oldest Jatropha plantations, indicating that microbial shifts occurred rapidly and lasted over the long term. Further studies dedicated to the functional implications of such structural shifts are needed since the genetic structure of essential microbial communities such as mycorrhizal fungi and nitrogen-fixing bacteria were proved sensitive to Jatropha.