December 25, 2012
Deforestation In The Amazon Affects Microbial Life As Well As Ecosystems
April Flowers for redOrbit.com - Your Universe Online
A troubling loss of diversity among the microbial organisms responsible for a functioning ecosystem is accompanying deforestation in the Amazon rainforest, an international team of microbiologists led by the University of Massachusetts, Amherst, has discovered."We found that after rainforest conversion to agricultural pastures, bacterial communities were significantly different from those of forest soils. Not only did the pasture soils show increased species numbers, these species were also less related to one another than in rainforest soil. This is important because the combination of lost 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," explains Klaus Nusslein, an expert in tropical rain forest microbial soil communities from UM Amherst.
Nusslein and colleagues, including scientists from the University of Texas at Arlington, the University of Oregon, Michigan State University, and the University of Sao Paulo, studied a large farm site in Rondonia, Brazil, over the past four years at the frontier where farmers convert rainforest to agricultural use by driving agriculture into pristine rainforest. The results of this study, which overcame limitations of earlier investigations to show changes in microbial diversity occurred over larger geographic scales, was recently published in Proceedings of the National Academy of Sciences.
Unlike earlier studies, the findings of this new study show that the loss of restricted ranges for different bacteria communities result in a biotic homogenization and net loss of diversity overall. The team worries that the loss of genetic variation in bacteria across a forest converted to agricultural use could reduce ecosystem resilience. The hope is that the results of this work will provide valuable data to decision makers about the future of the Amazon rainforest.
"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," says Jorge Rodrigues of the University of Texas at Arlington.
The team found important differences between the pasture and forest soil, Nusslein said. The number of bacterial species in the pasture soil was higher, for example, 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 to deal with additional outside stress," NÃ¼sslein said.
Although the Amazon represents half of the world's rainforest and is home to approximately one-third of Earth's species, the Amazon has one of the highest rates of deforestation. Nusslein and the team explain that agriculture is one of the largest and most dynamic parts of Brazil's economy, making dealing with standing rainforests in the tropics tricky. They assert, however, that it is vital that this issue be tackled.
"Our findings are especially important because they support the idea that microbes are impacted by human-caused environmental change," said Brendan Bohannan, director of the University of Oregon's Center for Ecology and Evolutionary Biology. "This knowledge is important because microbes are responsible for critical environmental processes, such as the recycling of nutrients, the production of clean water and the removal of pollutants."
James Tiedje of Michigan State University said that this study was unique and was conducted on a never-before-attempted scale.
"The systematic and large-scale sampling design of this study gave us the power to see the homogenization," he said.
Rodrigues and his team at UT at Arlington are compiling findings about the potential for recovery of the microbial diversity after pastureland is abandoned and returned to "secondary forest". Nusslein and his colleagues are simultaneously leading an effort to investigate how the redundancy of functions provided by soil microbes provides resilience to the effects of agricultural land use change to support a stressed ecosystem to recover stability.
"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 authors write.