The study explores an underappreciated way warmer temperatures are impacting ecosystems: decomposition

Our world is changing, and rising temperatures will change our natural ecosystems. Some of these changes will be straightforward, such as animals’ ranges creeping northward as they strive to maintain ideal temperatures. But other changes will be more complex, as warming sets off complex chain reactions that reverberate through these systems.

An important process in ecosystems is plant litter decomposition, where dead plant material is broken down by animals, fungi and microbes, making their nutrients accessible to the next generation of plants. How quickly this breakdown occurs – the rate of decomposition – is important for determining the ability of our ecosystems to retain carbon, which ultimately affects the levels of carbon dioxide (an important greenhouse gas) in the atmosphere, the main contributor to present-day global warming.

The speed at which this decomposition occurs is known to be affected by the composition of the plant community itself, i.e. the species present and their relative abundance, since different types of plants contain different types of nutrients. Just as you may find different nutrients in rice compared to wheat, when different plant species die, the nutrients that their decaying stems and leaves contribute to the ecosystem will differ.

Decomposition rates are also affected by the microbes that live in the soil, as different bacteria and fungi carry out the decomposition process at different rates. At the same time, rising temperatures can affect plant and microbial communities.

In a new study by Holden Arboretum ecologists Emma Dawson-Glass and Katie Staple, researchers explore how microbes, plants and warmer temperatures interact to change decomposition rates in a natural ecosystem. Their work has been published in the journal Functional environment.

“Our study is exciting because scientists have not extensively explored how changes in plant and decomposer communities will interact under global warming,” says Emma Dawson-Glass, a research specialist at the Steeple Community Ecology Laboratory and lead author of the study. “Studying how decomposition is affected by global warming can help us better understand how the function of our environment will change due to climate change. By improving our understanding of changes caused by global warming, we can also help better target climate intervention strategies.”

The new study builds on previous work that showed, through experimental warming in prairies, that higher temperatures changed the microbial community in a way that accelerated decomposition, but changed the plant community in a way that slowed decomposition. With both communities at work in nature, what do these conflicting processes mean for actual decomposition in ecosystems?

To find out, the team pitted these factors against each other in laboratory experiments to see what happens to decomposition rates when plants, microbes and high temperatures interact.

They found that soil microbial and plant communities interact in important ways. As expected, decomposition decreased when there was more slow-decomposing grass (Indian grass, Sorghastrum nutans) – but only when certain microbes were present in the soil. When soil microbes were exposed to higher temperatures, more Indian grass did not slow the decomposition process. This suggests that the microbial community has already shifted under global warming in ways that make it better able to cope with more Indian grass, which itself is more abundant under global warming.

This shift in the way microbes function may mean that changes in soil microbial and plant communities could interact to mitigate changes in decomposition under global warming. These findings promote a better understanding of how warming affects ecosystems, underscoring the importance of considering multiple simultaneous processes side by side in order to understand the outcomes.

“The effects of global warming are widespread, but incredibly subtle,” says Katie Staple, a Holden Forestry and Parks scientist and senior author on the paper. “The response of one component of the environment to global warming is almost certainly influenced by simultaneous shifts in others. Sometimes these confounding changes may exacerbate the effects of warming, but they may also mitigate the effects.”

“Uncovering the complex ways in which warming will modify different aspects of the environment, but also how these changes will interact with each other, will be a critical step in understanding how climate change is reshaping the world now, as well as in the future,” says Stibel.