Microbiota associated with the methane cycle in primary, secondary forest, and pasture in the Eastern Amazon

Author(s)

Jéssica Adriele Mandro

• Document type: Master's Dissertation
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Centro de Energia Nuclear na Agricultura (CENA/STB)
• Defense date: 2022-03-24

Examining board members

Tsai Siu Mui; Amanda Gonçalves Bendia; Cristina Rossi Nakayama

• Advisor: Tsai Siu Mui

Abstract

About 20% of the Amazon forest has already been deforested, a process driven mainly by forest-to-pasture conversion. These changes alter the intrinsic characteristics of the soil, causing microorganisms to respond quickly to disturbances. This scenario becomes alarming because specific groups of soil microorganisms act in the cycling of greenhouse gases (GHGs), such as methane (CH4). CH4 is the second most important GHG and, in the soil, its balance with the atmosphere is regulated by methanogenic (CH4-producing) and methanotrophic (CH4-consuming) microorganisms. Although the known influence of changes in land use on microbial communities, little is known about how this process actually affects the dynamics of soil CH4 with the atmosphere. Therefore, the objective of this dissertation was to evaluate the effects of land-use changes on microbial communities, mainly those CH4-related, in the Tapajós National Forest and adjacent regions in the Eastern Amazon. In the first study, the effects of forest-to-pasture conversion and forest recovery, and seasonality, on the microbial communities present in soils of primary and secondary forests and pastures were evaluated. Archaea and Bacteria, methanogenic and methanotrophic communities were evaluated by 16S rRNA sequencing and quantitative real-time PCR. The results indicated that the forest-to-pasture conversion modified the chemical properties of the soil, influencing the microbiota. The conversion increased the abundance of microorganisms related to CH4, mainly the proportion of methanogenic ones, indicating that pastures potentially act as sources of CH4, while primary and secondary forests, as sinks. While seasonality intensified the differences evaluated, mainly between forests and pastures. Finally, the results indicated the potential of secondary forest regeneration as a strategy for the recovery of chemical and microbiological soil patterns similar to those of primary forests. In the second study, the taxonomic and functional information on microbial communities was characterized, with emphasis on those associated with the carbon cycle (mainly CH4), present in forest and pasture soils, in the Eastern Amazon. Communities were assessed using a culture-dependent and culture-independent approach. The prospection and evaluation of microbial communities was carried out through enrichment and cultivation with the addition of CH4, followed by the comparison of the physiological profile of microbial consortia. Through the metagenomic sequencing of consortia and the recovery of metagenome-assembled genomes (MAGs), 16 high- and medium-quality MAGs were obtained, indicating the presence of new microbial genomes in Amazonian soils associated with methylotrophic and methanogenic metabolisms. Our results, from both studies, showed that changes in land uses have altered their properties, causing changes in the microbiota and, consequently, in their potential functions. With the discovery of new genomes in different soils in the Amazon, this situation becomes even more worrying due to the possibility of loss of species and ecological functions. However, forest recovery along with time (approximately 15 years) has a potential for the recovery of patterns similar to those of the primary forests, representing a promising strategy for the recovery and maintenance of ecosystem services. (AU)

• FAPESP's process: 19/26029-1 - Analysis of the methane cycle-associated microbiota in areas of primary forest, pasture and secondary forest in the Amazon
• Grantee: Jéssica Adriele Mandro
• Support Opportunities: Scholarships in Brazil - Master