Â鶹ÒùÔº

Burning fossil fuels has elevated atmospheric carbon dioxide, causing massive changes in the global climate including extreme temperatures and weather events here in the Midwest. Meanwhile, human activities have increased the amount of nutrients like nitrogen and phosphorus in grasslands and forests. These are the elements in fertilizer that make lawns greener and farmland more productive.

This overabundance of nutrients can lead to reduced water quality, the spread of invasive species and the loss of native species. However, it can also help plants capture carbon dioxide from the atmosphere and store it in the soil. This creates a paradox for environmental management: will reducing nutrient pollution make climate change worse by causing a release of carbon dioxide from the soil?

New research from the College of Biological Sciences in Nature Geoscience took advantage of a 40-year ongoing experiment at the University of Minnesota's Cedar Creek Ecosystem Science Reserve to study the impact of nutrients on carbon storage in abandoned croplands.

Professors Eric Seabloom, Elizabeth Borer and Sarah Hobbie and co-authors wanted to determine how nitrogen (and other nutrients associated with farmland) impacted carbon sequestration and whether reducing nutrient inputs could trigger a release of carbon dioxide back to the atmosphere.

The team discovered:

• Nutrient addition increased soil carbon storage after intensive tilling.
• These soil carbon gains persisted for at least three decades following cessation of fertilization and tilling.
• Lasting soil carbon gains occurred despite plant biomass rapidly returning to pre-fertilization levels, and as plant community composition recovered from the effects of fertilization.
• Carbon can remain stored in soils for decades following reduced nutrient pollution as long as the soil remains untilled.

"Understanding human impacts on Earth's ecosystems is challenging because these systems respond over multiple decades," said Seabloom. "Multidecadal experiments like the one underpinning this project are incredibly rare and valuable. The Cedar Creek Ecosystem Science Reserve and Long Term Ecology Research sites host some of the most significant long-term experiments in the world. They have been central to making the University of Minnesota one of the very top schools for ecology worldwide."

As agricultural methods become more efficient, increasing amounts of farmland in North America are being retired from production. This land presents an opportunity for carbon storage and ecological renewal. Future research is likely to focus on how retired farmland can be used by stakeholders to transform rural areas, promoting carbon storage and native species recovery alongside rural economic development and recreational access.