Diversity and life strategies of cyanobacteria and bryophytes within biocrusts in the context of mining tailings disasters in Brazil

This study investigates the impact of the Fundão Dam rupture in Brazil, one of the most severe industrial disasters globally, focusing on cryptogamic pioneer organisms, which are vital for forming biological soil crusts (biocrusts). These communities, found in superficial soil layers, play a crucial role in carbon and nitrogen fixation, enhancing soil aggregation, retaining moisture, and facilitating vascular plant establishment, making them essential tools for restoration efforts in mining tailings. Within this framework, we compared two sites - one impacted (IS) and one preserved (PS) - focusing on soil chemistry, biocrust taxa, and the life strategies of bryophytes and cyanobacteria. Soil was analysed for macro- and micronutrients, organic matter, and cation exchange capacity (CEC and ECEC). Biocrusts were identified through microscopy. Bryophyte life strategies were categorized based on traits such as spore size, reproductive strategy, and life form, while cyanobacteria were classified as pioneers, stayers, or stochastic species. Our findings revealed diverse biocrust species at both sites, with fugitive and colonist acrocarpous mosses dominating at IS, whereas perennial pleurocarpous mosses and leafy liverworts were exclusive to PS. Cyanobacterial life strategies were similar across sites. The impacted site had lower phosphorus levels and reduced CEC and ECEC compared to the preserved site. Four years after the rupture, bryophyte diversity, life strategies, and soil parameters still differ between IS and PS, highlighting the lasting impact of mining tailings. Given the ecological role of biocrusts, their inclusion in monitoring and restoration efforts is crucial for ecosystem recovery.