A first evaluation of biological soil crusts diversity in three distinctive rocky outcrops in Brazil

Biological soil crusts (biocrust hereafter) are communities structured by the interaction between bacteria, fungi, algae, cyanobacteria, lichens and bryophytes over the most superficial particles of the soil. These complex communities are mostly found in arid and semiarid regions, but they can also be conspicuous members of the vegetation in moist tropical ecosystems. This study presents the first taxonomic and ecological investigation of biocrusts in three prevalent Brazilian rocky outcrop types: ironstone, quartzite-sandstone, and limestone, while also assessing the distribution of these outcrop types across Brazil as potential biocrust habitats. We identified thirty-four bryophyte species (29 mosses, 5 liverworts), seven cyanobacteria genera, and one genus from each of the Charophyta and Chlorophyta algae groups. Twenty-four of the species (19 mosses and 5 liverworts) have never been previously reported in biocrusts associations in any ecosystem. Six microhabitats were characterized. Analysis of soil composition in the studied rocky outcrops highlighted pH, total acidity, phosphorus, organic matter, calcium, and iron concentrations as key distinguishing factors, emphasizing limestone as the most unique environment among the outcrops studied. Positive co-occurrence patterns were observed solely in ironstone and limestone outcrops, suggesting potential ecological interactions between mosses and cyanobacteria. The proportions of Brazilian rocky outcrops within Protected Areas (PAs) exhibited disparities, with ironstone and limestone outcrops being the most threatened, representing only 0.25 % and 5.11 % of PA sites, respectively. Our findings address crucial knowledge gaps within these unique ecosystems, offering valuable insights for biocrust research.