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The use of phytate as a phosphorus source by mycorrhizal and
non-mycorrhizal Scots pine (Pinus sylvestris)
talk
session 1: physiology
COLPAERT JAN V.1, ANDRÈ VAN LAERE1 &
KATIA K. VAN TICHELEN2
1Laboratory of Developmental Biology,
2Laboratory of Plant Ecology, Institute of Botany,
Katholieke Universiteit Leuven, Kardinaal Mercierlaan 92,
B-3001 Leuven, Belgium
ICOM1 Abstract
The use of phytate-P by mycorrhizal and non-mycorrhizal pine
seedlings was investigated. Mycorrhizal plants were either
inoculated with Thelephora terrestris or Suillus luteus.
Plants were grown for 9 weeks in a semi-hydroponic system
with P as the growth-limiting factor. Addition of a
relatively high concentration of soluble Ca-phytate resulted
in an increased relative growth rate (RGR) in both
mycorrhizal and non-mycorrhizal plants. The effect of the
mycorrhizal fungi on the use of the phytate-P was small. The
addition of an insoluble phytate to the growth substratum did
not result in an increase of the RGR and P uptake neither in
the non-mycorrhizal, nor in the mycorrhizal pines. Soil
phytate, which has a low solubility, is probably not a very
useful P source for Thelephora terrestris and Suillus luteus.
Nevertheless the external mycelia of these fungi exhibited a
substantial extracellular acid phosphatase activity. The
activity was correlated with the fungal biomass in the growth
substratum and decreased with an increasing P nutrition.
Phytase activity of the external mycelia could not be
detected although a low phytase activity could be observed at
the root surface. Mycorrhizas showed significantly higher
activities than uninfected roots. The orthophosphate, labile
and stable P fractions in the substratum were analysed at
harvest. In the mycorrhizal treatments the Pi pool decreased
significantly whereas the more stable P pool tended to
increase.