A model for microcolonial fungi growth on rock surfaces

Sub-aerial rock biofilms are supposed to be an important stage of primary succession in terrestrial ecosystems, and a substantial factor of the biodeterioration of monuments and buildings. Exposed rock surfaces of various origins and under different climatic conditions are colonised predominantly by fungi, but especially inherent for the sub-aerial biofilms is the presence of yeast-like black fungi often termed as microcolonial fungi (MCF). A conceptual model of rock dwelling fungal biofilms formed on exposed surfaces of solid rocks is proposed. An attempt to generalise the existing data on environmental factors determining the development of slow growing black fungi has been carried out. A simulation model of growth for a single fungal microcolony on a solid rock surface is proposed and analysed. The model exploits the idea of potential growth influenced by the environmental factors and organic nutrition. The effects of the factors are evaluated using the Liebig law of minimum. The analysis of the model sensitivity allows for the conclusion, that a continued lack of organic nutrition is a dominating environmental factor limiting growth of MCF on stone monuments and other exposed rock surfaces in European temperate and Mediterranean climate. However, significant gaps exist in our knowledge of the quantitative parameters and the processes of fungal growth and survival under the impact of natural and anthropogenic factors.