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Forests may be more resilient to climate change than previously thought.

A team of international researchers have found that increased inputs from plant roots can keep carbon levels in soil stable even as temperatures and nitrogen deposits in the atmosphere rise.

The collaborative research project, , looked at the effects of increased temperatures due to climate change and increased nitrogen in the atmosphere released by burning fossil fuels – two environmental threats that had been studied separately.

“There is a lot of uncertainty when these two antagonistic stressors are combined – which is why this study is so significant,” says Myrna Simpson, a professor in the department of physical and environmental sciences at the University of Toronto Scarborough who collaborated on the research conducted in the Harvard Forest in Massachusetts.

Earlier studies showed that increased temperatures caused forests to lose carbon while increases in nitrogen can result in carbon buildup. And warming alone can cause soil to lose carbon since heat speeds up decomposition and decomposition converts the carbon into CO2.

But the research team – led by Melissa Knorr and Serita Frey of the department of natural resources and the environment at the University of New Hampshire – found when rising temperatures were coupled with higher nitrogen levels, the plants added more carbon to soil by increasing their growth, activity and root turnover (the rate that their roots grow, die and decompose), maintaining soil carbon levels. 

Simpson, an associate director of the , has collaborated with Frey for many years on the effects of soil warming and nitrogen on the biogeochemistry of soil carbon in the Harvard Forest.

She says the research is unique because it includes both individual and combined treatments that represent combined impacts to temperate forests.

“Because of the advanced analytical capabilities in my laboratory and the Environmental NMR Centre at U of T Scarborough, we can uniquely decipher how multiple stressors alter the chemistry and potential long-term stability of soil organic matter at the molecular-level.”

Despite the research being conducted in Harvard Forest, Simpson says that soil warming has been shown to cause carbon loss worldwide. Excess nitrogen has also been found to suppress the microorganisms that keep forests healthy, even in forests that are rich in nutrients.

“We found that the way in which carbon flows within the soil biogeochemical cycle cannot be predicted from one stressor alone,” says Simpson, who is Canada Research Chair in Integrative Molecular Biogeochemistry. “It is likely that these observations may occur in other forests too.”

When it comes to future climate change research, Simpson says that there is much more work to be done. 

“We need more observational data because climate change’s impacts on ecosystems are complex and difficult to predict due to the diversity of ecosystem properties,” she says. “These ecosystems are influenced by more than one stressor, but we lack data to adequately predict the impacts.”

Simpson adds there is no single way to solve climate change in part because we don’t yet understand all of its effects.

She says that collaboration between researchers is critical. 

“Each expert can contribute data that can then be integrated into a more comprehensive assessment of how ecosystems are responding to stressors.”