Efeitos do fogo sobre as comunidades procarióticas do solo na Chapada Diamantina, Bahia, Brasil

Abstract

Wildfires, whether natural or anthropogenic, constitute threats to biodiversity, including that of microorganisms, which perform essential functions such as nitrogen fixation into usable forms and the regulation of carbon dioxide, both fundamental for soil maintenance. The action of fire can significantly reduce microbial richness, hindering processes such as the availability of nutrients for plants. In this study, we hypothesized that areas with wildfire incidence in the short term present lower microbial diversity compared to areas not affected by fire. Thus, the objective of this research was to analyze how wildfires influence the diversity of soil microorganisms in the region of Chapada Diamantina-BA. For this, the research was conducted in the Gerais do Rio Preto region, Chapada Diamantina, Bahia, where the number of fires has increased in recent years. ICMBio carries out, in the Conservation Unit of Chapada Diamantina National Park (PNCD), controlled burn events, known as ‘aceiros negros’ (black firebreaks), with the objective of reducing available biomass and, consequently, mitigating the spread of fire. Soil collections were carried out in areas subjected to the black firebreak in the years 2022 and 2023, allowing an evaluation based on chronosequence. Samples were collected at two depth layers (0–15 cm and 15–30 cm), in addition to control samples, all obtained in triplicate. The extraction and sequencing of soil DNA were carried out through the Amplicon technique, using the 16S rRNA genetic marker. The analysis of microbial composition revealed a significant diversity of prokaryotic phyla, indicating a functionally diverse and dynamic microbial ecosystem. Among the identified groups, the analysis revealed predominance of the phyla Acidobacteria, Actinobacteria, and Proteobacteria in the different environments studied, regardless of the fire history. On the other hand, Rhizobiales, Ktedonobacterales, and Solibacterales were more frequent in soils from unburned areas, suggesting lower tolerance to disturbances caused by high temperatures. Burning resulted in a decrease in microbial richness, especially in the superficial soil layers, without, however, significantly altering diversity as measured by Shannon and Simpson indices. In unburned soils, depth significantly influenced community composition, an effect that practically disappeared after disturbance. Altogether, the results reinforce that fire acts as a selective agent, favoring tolerant microorganisms and promoting structural changes in the community, while at the same time highlighting key taxa that may assist in monitoring and adaptive management of fire-prone ecosystems.