JACQUOT, EMMANUELLE, DIEDERIK van TUINEN, SILVIO GIANINAZZI & VIVIENNE GIANINAZZI-PEARSON.
Laboratoire de Phytoparasitologie INRA/ CNRS, CMSE-INRA, BV 1540, 21034 Dijon Cedex, FRANCE.
Application of sewage sludges to agricultural land is a widespread
practice because of their agronomic value as a source of plant nutrients and
organic matter. Nevertheless, such sludges often contain heavy metals or toxic
organic chemicals which can contaminate soils and cultures, making it is necessary
to establish risk evaluations for their use in agriculture. Arbuscular mycorrhizas
(AM) are candidates because of their common occurrence and central role in plant
health. Our research is aimed at (i) estimating the impact of sludges on populations
of AM fungi in agricultural soils, (ii) defining their sensitivity threshold
to chemical pollutants contained in sludges, and (iii) studying the mode of
action of the latter on the AM symbiosis, in order to specify conditions for
the use of AM fungi in phytotoxicity tests of sewage sludges or as bioindicators
of pollution in sludges.
Experiments have shown that root colonization of Medicago truncatula
by Glomus mosseae (BEG 12) is significantly decreased by sludges loaded
either with heavy metals or with toxic organic chemicals. This depressive effect
is not due to antagonistic microorganisms nor excessive available P levels in
the sludges. The impact of sewage sludges on fungal communities is being assessed
using a nested PCR technique we have developed to discriminate different fungal
species in planta and in soil, and a range of AM fungi is being screened
to select sensitive or tolerant isolates for use in phytotoxicity tests or soil
rehabilitation.
Key words: Arbuscular mycorrhiza - sludges - toxic organic chemicals - heavy metals - phytotoxicity test.