- Soil bacteria became more diverse as land was converted to pasture.
- However, biotic homogenization increased.
- Microbes impacted by human-caused environmental change.
RESEARCH from an international team of microbiologists has revealed a new concern about deforestation in the Amazon rainforest: a net loss in diversity among the microbial organisms responsible for a functioning ecosystem.
The group, which includes professors from The University of Texas at Arlington, University of Oregon, University of Massachusetts, Michigan State University and University of Sao Paulo in Brazil, sampled a 100 sq. km area at the Fazenda Nova Vida site in Rondonia, Brazil, a location in northwestern Brazil where the rainforest has been converted to agricultural use.
Their findings, in part, validated previous research showing that bacteria in the soil became more diverse over the years as it was converted to pasture, according to the announcement.
However, their findings contradicted prior thinking by showing that the loss of restricted ranges for different kinds of bacterial communities resulted in a biotic homogenization and net loss of diversity overall. There is a concern that the loss of genetic variation in bacteria across a converted forest could reduce ecosystem resilience, the researchers pointed out.
"We have known for a long time that conversion of rainforest land in the Amazon for agriculture results in a loss of biodiversity in plants and animals. Now we know that microbial communities that are so important to the ecosystem also suffer significant losses," said Jorge Rodrigues, an assistant biology professor at Arlington who was part of the research team and first author on the study findings.
The new research is described in a paper, entitled "Conversion of the Amazon Rainforest to Agriculture Results in Biotic Homogenization of Soil Bacterial Communities," which appears online in advance of publication in Proceedings of the National Academy of Sciences.
Klaus Nusslein, project director for the research and an associate professor of microbiology at the University of Massachusetts, said the team found important differences between the pasture and forest soils. For example, the number of bacterial species in the pasture soil was higher, but those species were also less related to one another than species in the forest soil.
"The combination of loss of forest species and the homogenization of pasture communities together signal that this ecosystem is now a lot less capable (of dealing) with additional outside stress," Nusslein said.
Research team member Brenan Bohannan of the University of Oregon explained that the group's findings were "especially important because they support the idea that microbes are impacted by human-caused environmental change" and noted that microbes are responsible for critical environmental processes, such as recycling nutrients, producing clean water and removing pollutants.
Scientists on the research team hope their work will provide valuable data to those making decisions about the future of the Amazon rainforest.
"The Amazon represents half of the world's rainforest and is home to one-third of Earth's species, yet the Amazon has one of the highest rates of deforestation," co-authors Vivian Pellizari, Siu Mui Tsai and Brigitte Feigl of the University of Sao Paulo said in a joint statement. "Agriculture is one of the largest and most dynamic parts of Brazil's economy, so dealing with standing rainforests in the tropics will be tricky, but nevertheless, it is vital that the issue is tackled."
Rodrigues said the research team is currently compiling findings about the potential for recovering the microbial diversity after pastureland is abandoned and returned to "secondary forest."
"Whether bacterial diversity will completely recover from ecosystem conversion will depend, in part, on whether the taxa lost due to conversion are truly locally extinct or whether they are present in the pasture sites but of such low abundance that they are undetectable in our study," the paper said.
The research team's work was supported by grants from the U.S. Department of Agriculture's National Institute of Food & Agriculture, Brazil's Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior and Fundacao de Amparo a Pesquisa do Estado de Sao Paulo.