UT Arlington researchers focusing on the Amazon recently found that widespread conversion from rainforest to pastureland has significant effects on microorganism communities that may lead to a reduction in the region’s role as a reservoir for greenhouse gas.
The Amazon rainforest is the largest terrestrial reservoir or “sink” for carbon dioxide, a gas that has been linked to climate change. Through photosynthesis, the Amazon absorbs 1.5 billion tons of carbon dioxide from the atmosphere every year in a process that requires input of nitrogen. That nitrogen, for the most part, comes from a process called nitrogen fixation - essentially microbes pulling nitrogen form the air into the soil.
The new paper, featured in the January issue of Applied and Environmental Microbiology, looks for the first time at the reaction of free-living nitrogen-fixing microorganisms called diazotrophs to the deforestation. Jorge Rodrigues, a UT Arlington assistant professor of biology, organized the work. Babur S. Mirza, formerly a postdoctoral fellow in the Rodrigues lab, is the paper's lead author.
“This study shows that although the diversity of diazotrophic microorganisms remains the same with the conversion from forest to pasture, the types of species found are different,” Rodrigues said. “Our next step is to measure how the rates of biological nitrogen fixation are influenced by community changes. Because the carbon and nitrogen cycles are so strongly linked, our previous results indicated that changes in carbon dioxide sequestration will occur.”
Rodrigues’ team gathered samples of soil from the Fazenda Nova Vida site in Rondonia, Brazil, one of three states in the country that accounted for more than 85 percent of deforestation from 1996 to 2005. They analyzed soil from a primary forest, a pasture established in 2004 and a secondary forest that resulted from the abandonment of a pasture in 1999.
The team used DNA analysis, specifically the nifH gene that is characteristic of diazotrophs, to measure the communities in the samples.
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