Soil incubation studies have shown that drying and rewetting cycles (DWCs) in Japanese forests and pasture soils significantly increase CO2 emissions. This increase appears to result from damage to microbial cells and changes in the composition of reactive metal-organic matter, leading to enhanced CO2 release.
Globally, the carbon dioxide (CO2) released by the decomposition of soil organic carbon is about five times higher than CO2 emissions produced by human activities. Therefore, understanding how climate change affects soil CO2 release is crucial.
A joint research team, which includes Dr. Hirohiko Nagano and Ms. Yuri Suzuki from Niigata University, along with researchers from Kyushu University and the Japan Atomic Energy Agency, conducted incubation experiments on forest and pastureland soils from ten sites across Japan. They found that CO2 emissions from soil rose sharply due to repeated drying and rewetting cycles (DWCs), which are anticipated as a consequence of changing precipitation patterns due to climate change. During these cycles, CO2 emissions were found to be 1.3 to 3.7 times higher compared to conditions where the moisture remained constant. Additionally, they reported a notable reduction in microbial biomass during DWCs, indicating that the breakdown of microbial cells contributed to the increase in CO2 due to fresh organic carbon produced during this process.
Moreover, the study highlighted that the rate of increased CO2 emissions due to DWCs was even more pronounced in soils rich in reactive metal-organic matter complexes. These complexes, which typically help in the stable accumulation of soil organic carbon, may become more accessible to microorganisms through the repeated cycles of drying and rewetting. As a result, organic carbon that typically resists decomposition could serve as a new source of CO2 emissions when subjected to DWCs.
Dr. Nagano emphasized that extreme weather events are becoming increasingly noticeable as a result of global warming. He also noted that this research will enhance our understanding of how such extreme weather can affect soil CO2 emissions, ultimately improving the accuracy of models predicting future global environmental conditions. The research team plans to conduct more in-depth studies on the mechanisms behind DWC-induced CO2 emissions across various global soils, in addition to assessing the effects in real-world outdoor settings.
