The dual symbiosis between arbuscular mycorrhiza and nitrogen fixing bacteria benefits the growth and nutrition of the woody invasive legume Acacia cyclops under nutrient limiting conditions

Background and aims Acacia cyclops is an invasive
species within Mediterranean ecosystems, characteristically
low in soil nutrients. Thus associations
with nitrogen-fixing bacteria (NFB) and arbuscular
mycorrhiza (AM) may provide an advantage to
these legumes. This study investigated the role of
AM and NFB in the growth and nutritional physiology
of A. cyclops.
Methods Seedlings were inoculated withnaturally
occurringNFB, Glomus mosseae or both, and
grown under glasshouse conditions for 5 months.
Plants were cultivated in sand and supplied with a
20 % strength nutrient solution.Xylem sap nutrients,
photosynthetic rates, biomass and chemical compositions,
were recorded.
Results The dual inoculation decreased the colonization
of both symbionts, compared to a single symbiosis witheither symbiont. Despite low colonization levels, the
dual symbiosis increased host biomass and relative
growth rates. This was associated with increased photosynthetic
rates and enhanced nutrition. Additionally,
dual symbiotic plants had enhanced N and P acquisition
and utilization rates. Xylem sap analysis showed
higher levels of NH4
+ being exported from the
roots to the shoots in the dual symbiotic plants
compared with other treatments.
Conclusions These findings suggest the dual symbiosis
is an important factor in the growth and development of A. cyclops under nutrient limiting conditions.