Southern California dryland soil sampled for nitrogen deposition study. Credit: Johann Püspök/UCR
Key points:
- Nitrogen can affect biological processes that in turn influence how soil stores carbon.
- Extra nitrogen in the air is affecting soil’s ability to hold onto carbon and keep it from becoming a greenhouse gas.
- Future studies may shed more light on how much dryland soil is being affected by nitrogen pollution.
New UC Riverside research suggests nitrogen released by gas-powered machines causes dry soil to let go of carbon and release it back into the atmosphere, where it can contribute to climate change.
Industrial manufacturing, agricultural practices, and vehicles all burn fossil fuels that release nitrogen into the air. Examining the effect of that nitrogen, the researchers were surprised to find that extra nitrogen causes dryland soil—the type that covers most of Southern California—to acidify and leach calcium. Calcium binds to carbon, and the two elements then leave the soil together.
For the study published in Global Change Biology, the research team sampled soil from ecological reserves near San Diego and Irvine that have been fertilized with nitrogen in long-term experiments. This allowed them to know precisely how much nitrogen was being added, and account for any effects they observed.
In general, soils resist dramatic changes in pH by releasing elements like calcium in exchange for acidity. As nitrogen acidified soils at some of the sites in this study, the soil attempted to resist this acidity by releasing calcium. As it did so, some of the carbon stabilized by association with the calcium was lost.
“It is a surprising result because the main effect seems to be abiotic,” said Johann Püspök, UCR environmental sciences graduate student and first author of the study. “That means bare patches of soil with no plant cover and low microbial activity, which I always thought of as areas where not much is going on, appear to be affected by nitrogen pollution too.”
Dryland soil, characterized by limited ability to retain moisture and low levels of organic matter, covers roughly 45% of Earth’s land area. It is responsible for storing a large amount of the world’s carbon.
“We need more information as to how widespread such acidification effects are, and how they work under non-experimental conditions of nitrogen deposition,” Püspök said.
However, since there is no quick fix for this phenomenon and no clear way to reverse the process once it has begun, researchers recommend reducing emissions as much as possible to help soil retain its carbon stores.
“Air pollution generated by fossil fuel combustion has an impact on many things, including human health by causing asthma,” said Peter Homyak, study co-author and assistant professor in UCR’s Department of Environmental Sciences. “It can also impact the amount of carbon these dryland systems can store for us. For many reasons, we have to get a handle on air pollution.”
Information provided by UCR.