Soil Methanogenesis Caused by Deforestation of the Amazon Rainforest for Agriculture

 By: Jaime Vargas

The figure has four graphs that demonstrate the relative abundances of methanogens in incubated soil samples from Pará and Rondônia. The y-axis is the abundance of methanogens, while the x-axis is the land type from which the soil was taken from. The PF stands for primary rainforest in green color, P stands for pasture in orange, and SF stands for secondary rainforest in blue. The bars with different colors within the graph demonstrate which genus of methanogen was more abundant in the soil samples. The two top graphs (A and B) had carbon dioxide (CO2) as a carbon source in the soil samples. The two bottom graphs (C and D) had sodium acetate (NaAOc) as the carbon source in the soil samples. Graphs A and C had soil samples from Pará, and graphs B and D had soil samples from Rondônia. Figure taken from Kroeger et. al., 2020.

The Amazon rainforest is one of the most diverse ecosystems in the world, but unfortunately this ecosystem has been reduced over time due to deforestation. The Amazon rainforest is known as a carbon sink, which is an area that takes up carbon compounds from the atmosphere like CO2. Deforestation in the Amazon rainforest leads to an increase in carbon compounds into the atmosphere by releasing the stored carbon, making the area a carbon source instead of a carbon sink. From deforestation new pastures and agricultural fields are born, and in the study by Kroeger et. al., the levels of methanogenesis are measured by comparing new pastures and the rainforest areas. The amount of methane produced can be linked to microbes in the soil, so the study focuses on culturing bacteria in different soil samples to determine if pasture soil increases methanogenesis or not. Soil samples were gathered from one cattle pasture and two rainforest regions called Pará and Rondônia. The samples were treated with distinct carbon sources and incubated; then DNA analyses were done to determine the abundance of methanogenic microbes in each soil sample. The results demonstrated that in pasture soil there was a higher abundance of methanogens compared to rainforest soils. The results show that loss of rainforest and increase in pastures leads to an increase in methanogenesis causing more green house gases to enter the atmosphere. Future research should focus on why pastures are more suitable for methanogens.

Reference:

Kroeger, M. E., Meredith, L. K., Meyer, K. M., Webster, K. D., de Camargo, P. B., de Souza, L. F., Tsai, S. M., van Haren, J., Saleska, S., Bohannan, B. J. M., Mazza Rodrigues, J. L., Berenguer, E., Barlow, J., Nüsslein Klaus, & Los Alamos National Lab. (LANL), Los Alamos, NM (United States). (2020). Rainforest-to-pasture conversion stimulates soil methanogenesis across the Brazilian Amazon. The ISME Journal, 15(3).