Summary

Plants inoculated with arbuscular mycorrhizal (AM) fungi utilize more
soluble phosphorus from soil mineral phosphate than non-inoculated
plants. However, there is no information on the response of soil
microflora to mineral phosphate weathering by AM fungi and, in
particular, on the catabolic diversity of soil microbial communities.
The AM fungus, Glomus intraradices was examined for (i) its effect on
the growth of Acacia holosericea, (ii) plant-available phosphate and
(iii) soil microbial activity with and without added rock phosphate.
After four-months culture, AM fungal inoculation significantly increased
the plant biomasses, while mineral phosphate amendment had no effect in
a disinfected soil. After 12-months culture, the biomasses of A.
holosericea plants growing in a non-disinfected soil amended with
mineral phosphate were significantly higher than those recorded in the
control treatment. The fungal inoculation also significantly stimulated
plant growth, which was significantly higher than that measured in the
mineral phosphate treatment. When G. intraradices and mineral phosphate
were added together to the soil, shoot growth were significantly
stimulated over the single treatments (inoculation or amendment). Plant
growth was positively correlated to the metabolization of ketoglutaric
acid, and negatively linked to the metabolisation of phenylalanine and
other substrates, which shows that microbial activity is also affected.
G. intraradices inoculation is highly beneficial to the growth of A.
holosericea plants in controlled conditions. This AM symbiosis optimises
the P solubilization from the mineral phosphate and affects microbial
activity in the hyphosphere of A. holosericea plants.

Keywords: Arbuscular Mycorrhizal symbiosis, Rock phosphate, Acacia.
Microbial Catabolic diversity