Soil Teeming With Diversity

When it comes to the diversity of soil bacteria, the otherwise species-rich Amazon is more like a desert, while the arid desert is a teeming microbial Amazon, Duke researchers have found. Their first-ever, continental-scale genetic survey of soil bacteria revealed that the primary factor that seems to govern the diversity of soil bacteria is soil pH. The acidic soils of tropical forests harbor fewer bacterial species than the neutral soils of deserts.

Because soil bacteria play a fundamental role in a vast array of ecological processes, the researchers say that their survey constitutes an initial step toward understanding that role.

Biologists Noah Fierer and Robert Jackson published their findings in an online edition of the Proceedings of the National Academy of Sciences. Fierer, a former post-doctoral scientist at Duke, is now assistant professor of ecology and evolutionary biology at the University of Colorado, and Jackson is a professor in Duke's department of biology and the Nicholas School of the Environment and Earth Sciences at Duke.

"Although soil bacteria have been studied for centuries, fundamental biological questions remain unanswered," says Fierer. "We probably know more about the organisms in the deepest ocean trenches than we know about the organisms living in soil in our backyards. The number of bacterial species in a spoonful of soil is likely to exceed the total number of plant species in all of the United States," he says.

According to Jackson, "microbes are very important for most of the critical processes in nature. They are extremely important for the cycles that make nutrients available to plants and animals and for much of the respiration that returns carbon back to the atmosphere as carbon dioxide."

In their survey, Fierer and Jackson collected and analyzed ninety-eight soil samples from across North and South America. The analyses revealed large differences among the samples in terms of diversity. The scientists then correlated that diversity with environmental factors, including latitude, temperature, and soil pH.