E. Facelli et al., Interactive effects of arbuscular mycorrhizal symbiosis, intraspecific competition and resource availability on Trifolium subterraneum cv. Mt. Barker, NEW PHYTOL, 141(3), 1999, pp. 535-547
We performed two glasshouse experiments to determine whether the presence o
f arbuscular mycorrhizal symbiosis reduces the intensity of intraspecific c
ompetition at low concentrations of available phosphorus (P), and whether t
his effect is modified by a reduction in light intensity. In the first expe
riment, Trifolium subterraneum cv. Mt. Barker was grown at different densit
ies in controlled conditions of light and temperature, and half of the pots
were inoculated with spores of the arbuscular mycorrhizal fungus, Gigaspor
a margarita. In the second experiment, the plants were grown in similar con
trolled conditions but the light intensity received by half of the pots was
reduced by >50%. The biomass and P content of individual mycorrhizal plant
s and the biomass response to mycorrhizal infection were drastically reduce
d as plant density increased. The effects of density on percentage infectio
n, shoot and root P concentrations, and root: shoot ratios were inconsisten
t. Generally reduction in light intensity did not alter these effects. Myco
rrhizal symbiosis increased intraspecific competition intensity thorough an
increase in the availability of soil P. This increase in competition was r
eflected in the greater size inequality of low density mycorrhizal treatmen
ts. Our results emphasize that the main effects of mycorrhizas at the indiv
idual level cannot be expected to be apparent at the population level, beca
use they are overridden by density-dependent processes.