Fractal analysis in studies of mycelium in soil

Abstract

Like many naturally irregular structures mycelia are approximately fractal; thus fractal dimension can be used to quantify the extent to which mycelia permeate space in relation to the extent of the system. Since it is important to be able to quantify both space filling at mycelial margins, i.e., `search fronts', and within systems, both surface/border and mass fractal dimensions are appropriate. The value of employing fractal geometry to describe mycelia is examined by comparison with information from other descriptors, in experiments examining the effects of extracellular concentration of the macronutrients NPK, and endogenous nutrient status of inocula, on development of mycelia of Hypholoma fasciculare, Phanerochaete velutina and Phallus impudicus. Mycelial morphology differed between species and was altered by both soil and inoculum nutrient status. Sensitivity to treatment effects was a major benefit of using fractal dimension (determined by box-counting) as a descriptor. However, complementary descriptors, including mycelial extent and total hyphal cover provided different information and all three should be used in combination. Further, though quantitative measures are attractive because of their objectivity they cannot describe all features of branching pattern, thus visual observation is also essential.