Air pollution causes dry soil to release carbon

High levels of nitrogen causes dry soil to release carbon it has been storing which contributes to the climate crisis, according to a new study.  

Cars, industrial processes and agricultural fertilisers all release nitrogen which has led to nitrogen rates in the atmosphere tripling since 1850.  

Now, scientists have investigated whether high levels of the gas affect soil’s ability to store carbon, but the results were different from what they were expecting.  

‘Because nitrogen is used as a fertilizer for plants, we expected additional nitrogen would promote plant growth as well as microbial activity, thereby increasing carbon put into soils,’ said Peter Homyak, study co-author and assistant professor in UCR’s Department of Environmental Sciences. 

But in certain conditions, particularly dryland soil, nitrogen causes the soil to acidify and leak calcium which binds to carbon.  

The team studied soil in reserves near San Diego and Irvine which had been fertilised with nitrogen during long-term experiments, so they could be aware of nitrogen levels.  

They found that as the soil acidified from the nitrogen, the soil attempted to rebalance the pH scale by releasing calcium. This means that some of the carbon which was bound to the calcium was also 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, which has a low level or organic matter, covers around 45% of the world, meaning it holds a large share of the world’s carbon.  

Future studies are in the works to see how much dryland soil is experiencing the same affects as the sample soil. Researchers say reducing emissions will help soil to retain its carbon stores.  

‘Air pollution generated by fossil fuel combustion has an impact on many things, including human health by causing asthma,’ Homyak said. ‘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.’

Photo by Johann Püspök/UCR 


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