A laboratory approach on the combined effects of granite bioreceptivity and parameters modified by climate change on the development of subaerial biofilms on cultural heritage

Abstract

Conservation of cultural heritage buildings and monuments may be negatively affected by the impact of climate change on substrates and colonizing microorganisms. In this study, four types of commercial granite, in which the bioreceptivity ranged from very low to very high, were inoculated with a multispecies microbial culture and exposed to different temperatures (18 and 24 °C) and levels of water availability (1 day, 3 days and 7 days of water availability/week) to simulate different climatic conditions. The effects on biofilm formation of the interactions between the substrate bioreceptivity and the environmental parameters were investigated. Biofilm growth and photosynthetic efficiency were monitored over 42 days by pulse-amplitude modulated (PAM) fluorometry and spectrophotometric colour measurement. The primary bioreceptivity of the granite was a determining factor in the organisms' capacity to attach to the substrate and interacted through the experiment with the climatic conditions by modifying the development of the microorganisms. Water availability was a limiting factor for the colonizing microorganisms, in terms of both growth and photosynthetic efficiency. At the higher temperature, metabolic reactions were enhanced under water restriction (but not under maximum water availability) and the microbial ecology was altered, leading to a higher proportion of cyanobacteria relative to algae.