Nutrient movement and mycelial reorganization in established systems of Phanerochaete velutina, following arrival of colonized wood resources.

The effect of arrival of wood resources, pre-colonized by Coriolus versicolor, Phlebia radiata, Stereum hirsutum, and Vuilleminia comedens, on mycelial systems of Phanerochaete velutina was studied in trays of nonsterile soil in the laboratory over 5 months. Morphological responses were quantified non-destructively using image analysis. In a parallel series of experiments, nutrient movement was also quantified non-destructively using (32)P monitoring with a scintillation probe and subsequently by destructively harvesting after 155 days. The presence of a fungus occupying a newly arriving resource had major effects on deployment of biomass and on the uptake and allocation of phosphorus in the established Pha. velutina system. The effects varied depending on the species occupying the new resource. Hyphal coverage was greater in the half of the system to which new resources were added. Following addition of new resources, there was massive redeployment of biomass away from regions with no new resource when the new resource was (1) uncolonized, (2) colonized by V. comedens, or (3) colonized by S. hirsutum (although to a lesser extent with the latter), but not with others. (32)P was taken up by Pha. velutina both in the vicinity of the inoculum and the new resource and was translocated to the new resource from both sites of uptake; however, the local supply contributed most. Bidirectional translocation also occurred. The results are discussed in relation to mycelial foraging strategies, nutrient translocation, and partitioning within mycelial cord systems.

Temporary phosphorus partitioning in mycelial systems of the cord-forming basidiomycete Phanerochaete velutina.

Mycelial cord systems, up to 50-cm diameter, of the basidiomycete Phanerochaete velutina (DC.: Pers.) Parmasto, a common woodland saprotroph, grown on non-sterile soil in model laboratory microcosms were baited, after 27 d, with pairs of fresh beech wood blocks (baits), placed at 10 d intervals behind the foraging colony margin. System development was quantified by image analysis. Mean radial extent and hyphal cover increased linearly with time until day 21, but declined before the mycelial systems reached the edges of the laboratory microcosms. The mass (DBM ) and border (DBS ) fractal dimensions of the mycelial systems changed with time but the ratio DBM ∶DBS became constant after 14 d. A separate central compartment containing the inoculum was supplied with 32 P orthophosphate and its translocation to wood baits monitored non-destructively for 73 d. Whilst total 32 P acquisition by wood baits increased linearly with time, the proportion of total allocated to baits varied significantly both temporally and according to the length of time that baits had been in contact with the mycelium. Most recently supplied wood baits were not the main sink for supplied phosphorus; rather, the rate of 32 P acquisition was initially greatest in baits from which egress of the fungus had already occurred. The rate of 32 P acquisition by the most recently added baits increased with time, supported by efflux from other wood baits, which had initially been the main sinks for translocated phosphorus. The results raise important questions about the ecological and functional significance of nutrient partitioning in cord systems and imply that 'observed' translocation, rather than being an absolute measure, indicates the degree to which phosphorus is loaded from a translocation stream in regions where it is being actively utilized and/or stored.