Rodrigues said researchers were surprised to find a ten-fold increase in the number of diazotrophic microorganisms in the pasture established in 2004, when compared to the primary forests. They theorize the pasture ecosystems rely on the diazotrophs more for nitrogen because of the continuous grazing from cattle, requiring constant regrowth of grasses.
"We observed a complete shift in the diazotrophic microbial community composition in response to the Amazon rain forest conversion to a pasture," Mirza said. "These differences an be attributed to the shift in the above ground plant community because we did see partial recovery of diazotroph community composition in the secondary forest, which have more plant species as compared to pasture."
Mirza said researchers are continuing their work with more sophisticated sequencing technologies and in-depth sampling.
Other co-authors on the new paper include Chotima Potisap, a visiting Ph.D. student from Khon Kaen University in Thailand; Klaus Nsslein, professor of microbiology at the University of Massachusetts; and Brendan J.M. Bohannan, professor at the Institute of Ecology and Evolution, University of Oregon.
The paper is titled "Response of Free-Living Nitrogen Fixing Microorganisms to Land Use Change in the Amazon Rainforest" and is available online here: http://aem.asm.org/content/early/2013/10/21/AEM.02362-13.full.pdf+html.
Despite worries about the effect these changes to the microbial communities may have on the carbon cycle, Rodrigues said there are some encouraging results. After pastures were abandoned and a secondary forest grew, partial restoration of the original diazotrophic communities was achieved, researchers said.
|Contact: Traci Peterson|
University of Texas at Arlington