Soil microorganisms are threatened by the replacement of forests with pastures in the Amazon – 09/21/2023 – Environment

Best known for its biodiversity of plants and animals, the Amazon also has a great diversity of microbial life, including in the soil. Important ecosystem services, such as storing methane that would go into the atmosphere, for example, are provided by microorganisms that live underground.

The replacement of forests with pastures, therefore, also poses a threat to bacteria, fungi and archaea. Integrating knowledge about these life forms into conservation, restoration and management efforts, therefore, becomes urgent for understanding and maintaining the Amazon.

The argument is defended in an article published in the journal Trends in Ecology and Evolution by a team of researchers from the University of São Paulo (USP) and collaborators from universities in the United States and the United Kingdom.

“Microorganisms are very important to maintain the macro: in this case, the functioning of the forest, the balance between animals and plants and the ecosystem services of rivers, among others”, exemplifies Júlia Brandão Gontijo, co-author of the work — developed with a grant from Fapesp during his doctorate at the Center for Nuclear Energy in Agriculture (Cena) at USP, in Piracicaba. Currently, Gontijo is a postdoctoral fellow at the University of California, in the United States.

A case extensively studied by the group is the replacement of microorganisms that consume methane (therefore, beneficial for climate balance) with those that emit the gas, when native vegetation is replaced by pastures. Cattle farming is responsible for 87% of land use changes in the Amazon.

“An unexpected finding we have had in recent years is that pastures have a greater local diversity of bacteria in the soil compared to forests. However, when analyzing the spatial scale, the microorganisms found in pasture soil are always the same , while in the forest there is greater variation from one place to another. The forest-pasture conversion, therefore, has led to a process of homogenization of soil bacterial communities”, says Andressa Monteiro Venturini, first author of the study, former postdoctoral fellow -doctorate from Fapesp and now a visiting researcher at Stanford University, in the United States.

One of the causes of this low spatial diversity of pastures, explains Venturini, is precisely the loss of endemic species of microorganisms, which can lead to the loss of important functions, such as the consumption of methane, a gas that causes the greenhouse effect.

FROM DEPOSIT TO SOURCE

In previously published work – in the journals Environmental Research and Science of The Total Environment –, the group had already shown that the conversion of forest to pasture changes the number of methane-producing archaea and methane-consuming bacteria, as well as the balance between these groups.

Forest soils typically act as methane sinks, preventing the gas from rising into the atmosphere. However, when converted into pastures, they become home to more methane-producing species and, consequently, emit more greenhouse gases. This shift from deposit to gas source is intensified with the removal of the topsoil and the addition of lime to reduce acidity.

“It’s not just the use of the soil that matters, but also the way it is managed”, explains Tsai Siu Mui, professor at Cena-USP and coordinator of the studies. Other work by her group had already shown how the conversion of forests into pastures favors the increase of antibiotic-resistant bacteria in the soil (read more here).

Both these studies and the one published now are part of a project supported under an agreement between the National Science Foundation (NSF), of the United States, and Fapesp through the BIOTA Program.

According to the researchers, soil as a source of greenhouse gases is little discussed in studies on national participation in global emissions. Therefore, they can be explored in new studies through the combination of environmental and molecular measurements (abundance of genes related to methane production and consumption), for example.

The paper further argues that by analyzing isotopic data, the metabolic pathways of methane production in soil could be identified, leading to a greater understanding of the microbial response to land use change. Furthermore, the union of environmental genomics with bioinformatics approaches, as well as machine learning, could predict emissions from this source, helping to avoid them, without losing sight of restoration and management strategies.

“Studies in this field can even provide the discovery of microorganisms favorable to native crops, such as fruits, which are already cultivated in the region, but lose productivity over time. The search for inoculants resulting from the region’s own biodiversity, for example , would be one of the paths for new studies that could help build an Amazonian bioeconomy”, concludes Tsai.

The co-authors of the work were Jéssica Mandro, who completed her master’s degree at Cena-USP with a scholarship from Fapesp and is currently pursuing a doctorate at the same institution.

The article Soil microbes under threat in the Amazon Rainforest can be read here.