Dynamics of mycelial growth and phosphorus partitioning in developing mycelial cord systems of Phanerochaete velutina: dependence on carbon availability

Mycelial cord systems, up to 50 cm in diameter, of the basidiomycete Phaner ochaete velutina, a common woodland saprotroph, were grown on unsterile soi l in model laboratory microcosms from either 4 or 16 cm(3) wood inocula. Af ter 48 d, systems were supplied at 10-d intervals with pairs of new 4 cm(3) beechwood resources placed behind the foraging colony margin, where possib le on opposite sides of the system. Image analysis was used to quantify rad ial extension, hyphal cover, the mass (D-BM) and surface fractal (D-BS) dim ensions of the mycelial systems and wood-resource bleaching activity. Mycel ial systems developing from small inocula had significantly (P less than or equal to 0.05) lower radial extension rates, hyphal cover and D-BM: D-BS r atio than those from large inocula. Initially, systems developing from smal l inocula also displayed significantly (P<0.05) slower wood-resource bleach ing activity than those from large inocula, suggesting that carbon limitati on affected both foraging behaviour and resource utilization. A separate ce ntral compartment containing the inoculum was supplied with P-32 orthophosp hate and its partitioning amongst wood resources was monitored nondestructi vely for 44 d. Total P-32 acquisition by wood resources was not significant ly (P>0.05) affected by inoculum resource size. However, the proportion of total acquired P allocated to resources, which varied according to the leng th of time that resources had been in contact with the mycelium, was depend ent upon inoculum size. The results support the hypothesis that phosphorus translocation is not a demand-driven process. We suggest that the time take n before the greatest rate of phosphorus withdrawal from a uniform transloc ation stream is dependent upon prior availability of carbon within colonize d resources.