RUDN University Soil Scientist showed how global warming increases the release of greenhouse gases from rice fields

The decomposition of organic matter in the soil is one of the stages in the carbon cycle between plants and the atmosphere. During decomposition, carbon is released into the atmosphere in the form of greenhouse gases - mainly methane and carbon dioxide - which become the main cause of global climate change. The intensity of this process depends, for example, on the ambient temperature or on soil microorganisms. Methane in the soil of rice fields is produced by single-celled archaea organisms, but for this they need intermediate substances that secrete plant roots. Therefore, the activity and number of microorganisms depends on the so-called priming effect - the roots secrete organic substances that ensure the vital activity of microorganisms. A soil scientist from RUDN for the first time found out how priming affects greenhouse gas emissions and how these processes change with global warming.

Soil scientists collected soil samples from rice fields in Hunan Province in southeastern China. The samples were sifted, the visible soil fauna and plant remains were removed, and water was added to simulate the flooded soil of rice fields. Then the samples were kept in plastic containers for 75 days in the dark at different temperatures corresponding to four seasons — 5 °C (winter), 15 °C (spring), 25 °C (autumn) and 35 °C (summer). The aim of the researchers was to measure how the priming effect changes the release of methane and carbon dioxide at different temperatures. In the experiment, soil scientists used sodium acetate, the simplest form of organic carbon produced by plant roots, as an auxiliary substance for archaea.

Soil scientists measured the level of greenhouse gas emissions every 2-5 days. On the 75th day, in soils with priming (with added sodium acetate), the release of methane increased by 153 times compared to samples without acetate. Moreover, the influence of priming depends on the temperature. For a temperature of 15 °C, the sensitivity to warming was the highest — a change in temperature by 10 ° C increases the release of methane by about 25 times. The release of carbon dioxide becomes greater the higher the temperature. Soil scientists explained this by an increase in the activity of microorganisms in warm conditions.

"The priming effect played a decisive role in the sensitivity of the decomposition of soil organic matter to temperature. At 5-15 °C, temperature changes significantly affect methane emissions - they increase by about 25 times. This means, for example, that during warm winters, the release of methane becomes the main cause of the greenhouse effect. Thus, the results of studies that do not take into account the priming effect should be taken with caution," - Doctor of Biological Sciences Yakov Kuzyakov, Head of the Center for Mathematical Modeling and Forecasting of Sustainable Ecosystems of the Agrarian and Technological Institute of the Russian Academy of Sciences.

The results are published in the journal Applied Soil Ecology.