For decades, scientists have known that deforestation is one of the greatest threats to the biodiversity of the Amazon rainforest, which has the highest number of plant and animal species of any region its size on the planet. Now, scientists have found out that deforestation is a threat to the diversity of bacteria in the soil, too.
In a study published online in the Proceedings of the National Academy of Sciences on Thursday, December 27th, an international team of scientists including Michigan State University professor James Tiedje, as well as researchers from the University of Massachusetts, University of Oregon, University of Texas at Arlington, and University of Sao Paolo, found that converting forest into cattle pasture reduced the number of species of bacteria present at first. Although the number of species then increased, so that there were more in any soil sample than before the land was cleared, they also became more uniform over a wide area by eliminating endemic species and replacing them with bacteria found in pastures all over the Amazon. This decreases bacterial diversity all thoughout the former rainforest as people clear the land for agriculture.
In a press release from the University of Texas at Arlington, lead researcher Jorge Rordigues said, “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, which are so important to the ecosystem, also suffer significant losses.”
This finding caused the scientists to worry that the loss of genetic variation in bacteria across a converted forest could reduce the ability of the ecosystem there to continue functioning.
"The combination of loss of forest species and the homogenization of pasture communities together signal that this ecosystem is now a lot less capable to deal with additional outside stress," Klaus Nüsslein, project director for the published research and associate professor of microbiology at the University of Massachusetts, said in the U.T. Arlington press release.
Brendan Bohannan, director of the University of Oregon's Institute of Ecology and Evolution, elaborated on the importance of soil bacteria and effects of biodiversity loss in a University of Oregon press release.
"Our findings are especially important because they support the idea that microbes are impacted by human-caused environmental change," said Bohannan. "Land-use change is part of the suite of human-caused environmental changes known as global change. Understanding how microbes respond to such changes is especially important because microbes are responsible for environmental processes that sustain all of life — the recycling of nutrients, the production of clean water, the removal of pollutants and more."
"Most importantly," Bohannan said, "we found that this occurs in part because microbes unique to the forest are displaced when a forest becomes a farm. Such endemic types are especially important in ecosystems, because they have unique characteristics that contribute to an ecosystem's ability to maintain function when the environment changes."
Tiedje, MSU professor of crop and soil sciences, said the study was unique because of its large scale. He and his fellow scientists sampled a 100 square kilometer area, about 38 square miles, in the Fazenda Nova Vida site in Rondônia, Brazil, a location where rainforest has been converted to agricultural use.
“The systematic and large-scale sampling design of this study gave us the power to see the homogenization,” Tiedje said in a press release from Michigan State University.
Vivian Pellizari, Siu Mui Tsai, Brigitte Feigl from the University of Sao Paolo wrote in a joint statement, "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. 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.”
U.T. Arlington's Rodrigues said the research team is currently compiling findings about the potential for recovery of the microbial diversity after pastureland is abandoned and returned to secondary forest. As he and his fellow authors wrote in their paper, "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."
In the abstract to their paper, the scientists concluded, "Given that soil microbes represent the majority of biodiversity in terrestrial ecosystems and are intimately involved in ecosystem functions, we argue that microbial biodiversity loss should be taken into account when assessing the impact of land use change in tropical forests."