RUNNING TITLE: Exotic tree species and soil microflora functionalities

ABSTRACT The response of microbial functional diversity as well as its
resistance to stress or disturbances to the introduction of an exotic tree
species, Acacia holosericea, ectomycorrhized or not with Pisolithus albus was
examined. The results show that this ectomycorrhizl fungus promote drastically
the growth of this fast growing tree species in field conditions after 7 years
plantation. Compared to the crop soil surrounding the A. holosericea plantation,
this exotic tree species associated or not with the ectomycorrhizal symbiont,
has induced strong modifications in soil microbial functionalities (assessed by
measuring the patterns of in situ catabolic potential (ISCP) of microbial
communities) and reduced soil resistance to increasing stress or disturbance
(salinity, temperature, Freeze-thaw and wet-dry cycles. In addition, A.
holosericea has strongly modified the structure of arbuscular mycorrhizal fungus
communities. These results show clearly that exotic plants may be directly
responsible of important changes in soil microflora affecting the structure and
functions of microbial communities. These findings have to be considered during
the management of exotic species as well as the opportunity to use these exotic
fast growing trees to rehabilitate degraded areas has to be questioned.

Key words: Ectomycorrhizal symbiosis; catabolic diversity; Acacia holosericea,
Pisolithus albus; soil microbial communities