Open-Air Laboratories

For over a decade, the U.S. Department of Energy has managed a collection of large, outdoor field experiments to monitor the effects of elevated CO₂ levels in real ecosystems. Observing stations and CO₂ injectors were established in a variety of ecological zones, and researchers have been collecting empirical data on how the extra greenhouse gas in the air affects the plants and other life present.

Sweetgum plantation in Tennessee
photo courtesy of Steve Eberhardt / ORNL

Kuske's team takes its soil samples from six of these study sites, chosen to span a diverse range of habitats within the United States. In most of the sites, plant growth increases in response to the elevated CO₂. But how much of that carbon remains locked up in plant matter, safely out of the atmosphere? That depends on the microbes in the soil, and it is one of Kuske's principal research objectives to assess the microbes' response to the added CO₂, an effort that began in earnest about a year ago. One of the major challenges is to identify trends in microbial populations that are important at the landscape level, which requires many samples and a blend of metagenomic and other measurements.

Desert shrubs, grasses, and soil crust in Nevada
photo courtesy of Lynn Fenstermaker

Kuske's early results show that a soil community's response to the enriched CO₂ atmosphere is varied and complex; each ecosystem has a different response pattern. At some sites, the total microbial biomass goes up or down. In some cases, the fungal populations appear to change the most, while in others it's the bacteria. In the Nevada desert site, for instance, there was no observed change in fungal populations, but a population of bacteria called cyanobacteria diminished substantially. This may be significant because cyanobacteria in arid lands are responsible for many of the services normally provided by plants elsewhere: absorbing carbon from the air through photosynthesis, fertilizing, and stabilizing the soil against erosion. Arid lands—including deserts, arid grasslands, and shrub lands—make up one-third of all the land on Earth.