Deforestation and pastures in the Amazon: impacts of soil acidity management and of Urochloa brizantha rhizosphere on the methane microbial community

Author(s)

Leandro Fonseca de Souza

• Document type: Doctoral Thesis
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Centro de Energia Nuclear na Agricultura (CENA/STB)
• Defense date: 2020-07-02

Examining board members

Tsai Siu Mui; Teotonio Soares de Carvalho; Rodrigo Mendes; Vivian Helena Pellizari

• Advisor: Tsai Siu Mui

Abstract

In the Amazon region, pastures are the main land-use after deforestation. This land conversion affects soil methane cycling, changing the soils from being a sink of atmospheric methane to becoming a source. Here, we evaluate how the management of pastures can affect this process, considering the rhizosphere of the common pasture grass Urochloa brizantha cv. Marandu and soil liming to pHs 5.8-6.5. We also tested the importance of soil acidity in forest soils to methane sinking. Two greenhouse experiments were set using forest and pasture soils from eastern and western Amazonia, incubations with 13CH4 for DNA stable isotope probing (SIP-DNA) and field measurements (gas flux, soil chemistry, etc.). The methane cycling microbiota was accessed by quantifying its marker genes pmoA and mmoX (methane oxidation), mcrA (emissions) and by high throughput sequencing of 16S rRNA gene. We observed that acidic pasture soils with grass coverage had up to 35% higher methane sinking, and a 10-fold reduced abundance of methanogens in the grass rhizosphere vs bulk soil, comprising Methanosarcina spp., Methanocella spp., Methanobacterium spp. and Rice Cluster I. Furthermore, liming pasture soils can increase methane sinking under high concentrations of this gas by active methanotrophs Beijerinckiaceae (type II) and Methylocaldum sp. (type I), and reduce sinking under atmospheric concentrations, with no changes on methanotrophs or methanogens absolute abundance. We also find that liming acidic forest soils can reduce its methane oxidation, shortly turning them to sources, with no changes on methanotrophs or methanogens absolute abundance. These results show the potential of pasture management by liming soils and conserving a grass coverage on soils to mitigate soil methane emissions. It also indicates the need of research to validate these results under field conditions, considering the rain seasonality in the region and under soil moisture saturation, as favorable conditions to methanogenesis (AU)

• FAPESP's process: 18/09117-1 - ACTIVE MICROBIOTA IN METHANE SEQUESTRY IN FOREST AND PASTURE SOILS REVEALED BY STABLE ISOTOPE PROBING AND METAGENOMICS
• Grantee: Leandro Fonseca de Souza
• Support Opportunities: Scholarships in Brazil - Doctorate