Soil carbon, nitrogen mineralization and climate change

New research reveals the relationship betweensoil carbon, nitrogen mineralization and climate change

In a long-term study and the first of its kind, a group of scientists, led by Ashley Kaiser, an assistant professor of soil ecology at the Stockbridge College of Agriculture at the University of Massachusetts, discovered that soil carbon is primarily responsible for determining whether mineralized (absorbable) nitrogen is available in the soil in the form of ammonium, nitrate, or nitrous oxide.

To simplify the above, pure atmospheric nitrogen is an element that is difficult for the soil to absorb; Therefore, the process of mineralization (converting it into compounds) is considered essential so that the soil can benefit from it. Among the most important major nitrogen compounds in soil are: ammonium; But we can also find other nitrogen compounds that the soil does not benefit from, and may even have a negative effect.

Unwanted nitrogen compounds include nitrates, which dissolve easily in water and seep into streams and rivers; Thus, it contributes to the proliferation of toxic algae, as well as nitrous oxide, which is considered 300 times more powerful than carbon dioxide in promoting global warming.

Soil carbon and the role of microbes

Research recently published in Biogeochemistry Letters shows that the relationship between soil carbon and nitrogen appears to exist across different ecosystems. For those who do not know, by soil carbon we mean the inorganic carbon the soil contains, which we can find in the form of compounds such as carbonates, as well as organic carbon, which we find in a large number of organic compounds, and soil carbon plays a major role in the carbon cycle.

Kaiser, one of the study’s lead authors, says: “All living organisms need nutrients in specific proportions, without deficiency or excess, just like humans; She takes in the nutrients she needs, then gets rid of the excess in order to maintain good health.”

As we know, there are billions of microbes in every atom of soil. These microbes represent the dominant form of life on Earth, and depend on both: carbon and nitrogen. In order to survive, it takes the carbon and nitrogen it needs, and the excess it needs, it processes and returns to the soil, a process known as “mineralization.”

The important role of microbes in the soil is that they break down organic materials, such as: dead leaves, rotting wood, and the remains of countless microbes. This is to obtain carbon and use it as fuel for its vital processes, then get rid of the excess. This process is called “carbon mineralization.”

Microbes also mineralize the nitrogen present in these dead remains, converting it to ammonium. As we mentioned earlier, ammonium is the preferred food for plants, through which they can absorb nitrogen, but microbes can also convert nitrogen into nitrate, which dissolves easily in water.

When nitrates are abundant in soil, they can flow into streams and rivers, feeding extensive algal communities, many of which are toxic to aquatic plants and animals. Furthermore, the mineralization process can also produce nitrous oxide, a greenhouse gas hundreds of times more potent than carbon dioxide.

Relationship between carbon and nitrogen

What Kaiser and her team discovered is that the amount of carbon in the soil is closely related to how microbes process nitrogen. “When soil carbon stocks are high, microbes need more nitrogen to consume for themselves,” Kaiser says. This is to balance her diet. While more nitrogen consumption by microbes means that they produce less nitrate, it also means that they produce less ammonium, which is needed to feed plants.”

The above can also be reversed: when there is less carbon in the soil, microbes will consume less nitrogen for themselves; Thus producing more ammonium and nitrate compounds, and possibly nitrous oxide.

From the above, we can say that carbon is the key, which is what Kasir and the study’s lead author, Allison Gill, discovered. They tested this theory at 14 sites across the United States. These sites include diverse ecosystems, including tundra, boreal forests, deserts, and grasslands. They used data collected over 40 years by the National Science Foundation (NSF), and used it as a powerful tool to assess the impact of carbon concentration. In the soil inNitrogen cycle.

Kaiser says: “I and all of my participants in this exciting study were surprised by the results we reached about the effect of soil carbon on nitrogen mineralization, results that we had not previously imagined. Which means that our outlook towards many different environmental and agricultural systems will change in one way or another, as well as the way we deal with these systems in the short and long term.”

The discovery of this close relationship between soil carbon and nitrogen is important and affects many aspects, from agriculture to climate change mitigation solutions, which depend on storing carbon in the soil; Therefore, when discussing solutions to reduce the amount of carbon in the atmosphere by storing it in the soil, we must be aware of what this will entail.