Development of mycelial cord systems of Phanerochaete
velutina (DC.: Pers.) Parmasto from 4-cm3 inocula on a
nutrient-depleted non-sterile soil was studied in laboratory microcosms
using
image analysis techniques. Cord
systems were ‘baited’ after 13 d growth with either fresh,
non-sterile 4-cm3 wood baits or control Perspex® blocks
of the same contact area placed behind the foraging mycelial front.
After 26 d growth, mycelial ‘patches’ arose by
dedifferentiation of consolidated mycelial cords in both wood- and
Perspex-baited cord systems. ‘Patches’
comprised fine, highly branched separate hyphae extending radially from
points of aggregated hyphae in cords.
‘Patches’ and cords could be readily distinguished by image
analysis and the areas covered by patches and cords
could be measured and compared. Whilst the total hyphal cover of Perspex-
and wood-baited systems did not
differ significantly (P>0·05), patch cover in
wood-baited systems was up to 10 times greater than in Perspex-baited
systems. Patches were temporary structures, regressing more rapidly with
age than mycelial cords. Patch
development ceased after application of a nutrient solution which
replenished phosphate levels in the soil. Wood-baited mycelial systems
displayed
significant developmental polarity (P[les ]0·05) of both
total hyphal cover (patches
plus cords) and hyphae in patches towards the ‘baited’
sector of cord systems after 42 d, which corresponded with
peak patch development. However, significant (P[les ]0·05)
developmental polarity of the mycelial systems along the
bait-inoculum line could be detected 8 d before patch formation when assessed
by fractal geometry. Radiotracer
studies showed that mycelial patches were not sinks for supplied
32P, but that they were sites of increased nutrient
uptake capacity compared with that of mycelial cords. We discuss the need
for
mycelial cord systems to balance
allocation of mycelial biomass between the two essential processes of colonizing
wood resource units, and the
acquisition of soluble inorganic nutrients from soil.