Briófitas, cianobactérias e algas em crostas biológicas do solo: diversidade e padrões ecológicos em afloramentos rochosos brasileiros

Abstract

Biological soil crusts (BSC or biocrust) are communities structured by the interaction between bacteria, fungi, eukaryotic algae, cyanobacteria, lichens and bryophytes that live interacting intimately with the most superficial particles of the soil. Biocrusts occur predominantly in drylands, where they provide important ecological services such as soil aggregation, moisture retention and nitrogen fixation. Unfortunately, many BSC communities remain poorly explored, especially in the tropics. In this study we summarize the knowledge about BSCs in Brazil, compare Brazilian BSCs communities to others around the world, describe why BSCs can be considered ecosystem engineers and propose their use in the colonization of other worlds. We also explore for the first time ecological aspects of biocrusts in three of the most common types of rocky outcrops in Brazil — ironstone, quartzitesandstone and limestone. We present a floristic list, a characterization of microhabitats and soils where biocrusts grow, a description of positive co-occurrence patterns and a creation of a relevant framework for future effective conservation actions to biocrusts within outcrops. Finally, we explored the growth preferences of the common biocrusts moss Bryum atenense relative to calcium concentrations reported from Brazilian rocky outcrops. The findings of this study show the importance and relevance of biological soil crusts in Brazilian ecosystems and emphasized the potential uses of biocrusts in processes aimed at the recovery of degraded areas. Moreover, Brazilian outcrops are refuges for moss-dominated crusts, which have adaptations to grow in different microhabitats, including those with harsher environment conditions. We encourage future inventories and conservation efforts involving rocky outcrops throughout the world, as biocrusts in these ecosystems are poorly studied and commonly ignored. Lastly, the experiment with B. atenense in a gradient of calcium concentrations suggest issues about adaptability and ecotypes within biocrusts taxa.