Thermotolerance in Miniature: Heat Resilience of Moss Propagules From Brazilian Ferruginous Rocky Outcrops

Harsh environments present substantial challenges to most organisms, making survival and thriving difficult. Such conditions often include extreme temperatures, intense radiation, strong winds, and very low or high humidity levels, resulting in a limited availability of resources like water and nutrients. Deserts, with their extreme heat and scarce water, and Brazilian ferruginous rocky outcrops (Cangas), known for their extreme temperatures, nutrient-poor soils, wildfire events, and limited water, are prime examples. Despite these harsh conditions, Cangas host specialised flora, including rare angiosperm species, and diverse mosses and liverworts adapted to water scarcity and high solar radiation. However, their adaptations to heat stress are not well understood. Our study is the first to investigate the thermotolerance of bryophyte asexual propagules in two common moss species found in Cangas, in the context of forest fires, focusing on Bryum atenense R.S. Williams (Bryaceae) and Campylopus savannarum (Müll. Hal.) Mitt. (Dicranaceae). We subjected B. atenense tubers and C. savannarum detached leaves to heat treatments at 120°C, 140°C, and 160°C for 5 and 30 min, alongside a control group. Results showed that C. savannarum leaves lack thermotolerance, whereas B. atenense tubers exhibited notable resilience, as evidenced by protonemata production up to 54 days after treatment, with 60.4% regeneration at 120°C for 30 min and 58.3% at 160°C for 5 min. This study represents the first record of thermotolerance in bryophyte asexual propagules in Cangas, documenting the highest level of thermotolerance known for moss propagules. It offers valuable insights into moss resilience in harsh environments and their potential responses to wildfires and global warming.