Diverse soil communities can help offset impacts of global warming

In a long-term study, researchers showed that small soil animals can limit the effects of climate change, which would otherwise stimulate the loss of carbon from the soil into the atmosphere.

The study provides key new insights into how the interactions between organisms in the soil are likely to be critical for controlling the changes in carbon cycling under current and future climate scenarios. The results were published in the Proceedings of the National Academy of Sciences.

Decomposition of dead plant and animal material by soil microorganisms generates an annual global release of 50 to 75 petagrams of carbon -- in the form of carbon dioxide and methane -- into the atmosphere (1 petagram equals 1 billion metric tons). This amounts to almost ten times the greenhouse gas production of humans worldwide. Scientists have known for a long time that warming has the potential to accelerate this process, leading to increased carbon emissions that will accelerate climate change through a dangerous feedback cycle. However, until now, little has been known about which ecosystems will be most affected and why.

The study -- an international collaboration between researchers at the Yale School of Forestry & Environmental Studies (F&ES), the University of Helsinki, the Institute of Microbiology of the ASCR in the Czech Republic, and the University of New Hampshire -- was designed to shed light on this issue.

"In disturbed environments, where soil animals are not present, the feedback between climate change and microbial carbon production was strong," said Thomas Crowther, a postdoctoral fellow at Yale F&ES and lead author of the study. "Meanwhile, when the soil community is healthy and diverse, we saw that animals feed on the microorganisms, limiting the feedback effects."

In the same way that Yellowstone's wolves regulate plant diversity by controlling the number of grazing elk, the researchers found that small animals -- such as insects and worms -- can play a similar regulatory role in soil ecosystems by feeding on the microbes that can trigger increased carbon emissions.

But this "top-down" control matters only when there are no limitations to the production of nutrients at the bottom of the food web -- such as those conditions that would occur as a result of climate change, Crowther said. "As a result of climate change, there's going to be more nitrogen deposition, it's going to be warmer -- many of the things that limit fungal growth are going to be alleviated," he said. "And by stimulating microbial activity it will trigger higher carbon emissions. So when those 'bottom up' limitations are gone, the grazing animals become even more important."

The study was conducted at the Harvard Forest long-term climate change research site, where researchers were able to examine how atmospheric warming and nitrogen deposition are likely to alter natural ecosystems under future climate change scenarios.

As part of the experiment, researchers manipulated the soil communities to establish four levels of community complexity, allowing them to see which types of community would be most affected by the global change factors such as warming temperatures.

The study highlights the importance of understanding biological processes if scientists are going to be able to predict the consequences of climate change, said Hefin Jones, a professor at Cardiff University and a leading expert in climate change research. He was not affiliated with the study.

"Our current understanding of carbon cycle feedbacks to climate change stem mostly from the physical sciences; this study shows that precise global predictions can be achieved only if we understand the interactions between organisms," he said.