Encounter with new resources causes polarized growth of the cord-forming basidiomycete Phanerochaete velutina on soil

The development and physiology of cord-forming saprotrophic basidiomycetes, which form extensive and persistent mycelial networks in woodland ecosyste ms, can be conveniently studied on non-sterile soil in laboratory microcosm s mimicking field conditions. Morphological responses of Phanerochaete velu tina mycelial systems to resource encounters, and decay partitioning follow ing encounters, varied according to whether simulated woody litter was unst erile or autoclaved and on whether encounter took place at the mycelial for aging front or behind the margin (simulating litter fall onto established s ystems in the field). Results show that encounter of discrete resources by P. velutina is rapidly communicated to the entire mycelial system; that res ource capture takes high priority at the expense of continued system extens ion and decay-derived carbon reallocation; and that polarized growth toward newly encountered resources, previously considered to occur infrequently w ith this species, may be readily detected using image analysis techniques. Potential advantages of polarized development of P. velutina are discussed.