- A study, consisting of two sequential greenhouse experiments, was
designed to determine the effects of soil liming upon the fungal
partner in a mycorrhizal association. A Willamette Valley foothill
soil, of the Jory series, was limed in increments to achieve a range
of acidity and alkalinity. The P-deficiency and P-fixing capacity of
this soil, and its strong acidity (pH 5 in 2:1 water:soil suspension)
provided stressed conditions favoring mycorrhizal benefit.
Two vesicular-arbuscular mycorrhizal (VAM) fungal species,
Glomus fasciculatum and Glomus mosseae, were introduced into separate
soil treatments and compared with non-inoculated control treatments.
Stem heights, stem diameters, and leaf numbers of sweetgum
(Liquidambar styraciflua L.) seedlings were measured monthly throughout
the study, along with periodic monitoring of soil pH, soil nutrient
levels, and VAM colonization of the roots.
The experimental variable involving soil pH, mycorrhizal species,
and their interactions exhibited significant effects on seedling
Growth of non-mycorrhizal seedlings remained minimal throughout the growing season, and appeared independent of lime applications. The
efficiency of the fungal symbionts in stimulating growth was influenced
by their adaptability, or tolerance, to different soil pH environments.
In this study, G. fasciculatum was more efficient in acid to neutral pH
conditions, and generally tolerated a wider pH range than G. mosseae.
Comparatively, G. mosseae proved more efficient in neutral to alkaline
pH conditions and showed less tolerance to acid conditions.
The percentage colonization of sweetgum roots by the VAM fungal
species corresponded to their respective enhancements of growth.
However, G. mosseae exhibited a lower per cent colonization than
G. fasciculatum at any pH regardless of any larger growth responses
which it induced. At unlimed (pH 5) levels, there was no seedling
response to G. mosseae although there was root colonization.
Most nutrient concentrations in leaf tissue were little affected
by lime applications; some were more affected by VAM colonization.
Plant levels of Al, Fe, and Mn were noticeably influenced by both
lime applications and VAM colonization. Total nutrient uptake and
assimilation was substantially greater in all VAM seedlings because
of their larger biomass.
If maximum benefit from a mycorrhizal association is to be
achieved, careful consideration should be given to employing fungal
species tolerant of particular soil pH regimes.