Fungal growth response to carbon and nitrogen limitation: A theoretical model

Abstract

A model of fungal growth in soil is described. Two biomass components, cell walls and cytoplasm are considered. Allocation of assimilates to cell wall and cytoplasm synthesis and the relative rate of cytoplasm translocation vary according to C and N availabilities. Model behaviour in relation to substrate supply is examined. For single substrate additions, active mycelium (cytoplasm-filled hyphae) shows a positive correlation to substrate availability, while total hyphal length (cytoplasm-filled + evacuated hyphae) shows an inverse response. For continuous substrate additions, the model predicts that equilibrium levels of active mycelium depend primarily on substrate input rate and yield efficiency and are independent of other parameters controlling substrate availability. Model assumptions about biosynthate allocation and cytoplasm translocation influence N mineralization and immobilization patterns. The model suggests that critical C:N ratios change during decomposition as the fungal biomass develops. The advantages conferred by the mycclial growth form, in terms of conserving energy and nutrient elements in resource-poor environments, are discussed.