Drying and rewetting cycles substantially increased soil CO2 release

A collaborative research group consisting of Dr. Hirohiko Nagano and Ms. Yuri Suzuki of Niigata University with researchers of Kyushu University and the Japan Atomic Energy Agency conducted incubation experiments on forest and pastureland soils at 10 locations across Japan. The research group revealed that the amount of CO₂ released from soil increases significantly due to repeated drying and rewetting cycles (DWCs) expected to be caused by changes in precipitation patterns due to global warming. Here, the CO₂ release under DWCs were 1.3- to 3.7-fold greater than under continuous constant moisture conditions. They also observed a significant decrease in microbial biomass under DWCs, suggesting that the newly supplied organic carbon resulting from the destruction of microbial cells by repeated DWCs contributed to the increase in CO₂ release.

In addition, it was found that the increased rate of CO₂ release due to repeated DWCs was greater in soils with a higher abundance of reactive metal-organic matter complex. This suggests that the reactive metal-organic matter complex, considered important as a stable accumulation mechanism for soil organic carbon, may become more readily available to microorganisms through repeated DWCs. Thus, organic carbon that has previously avoided decomposition may become a new source of CO₂ release under DWCs.

Dr. Nagano pointed out that extreme weather phenomena are becoming more evident due to global warming. Furthermore, he says that the results of this research will lead to a detailed elucidation of the impact of extreme weather phenomena on soil CO₂ emissions, contributing to improving the accuracy of prediction models for the future of the global environment. In the future, they plan to conduct impact assessments and mechanism verification in outdoor environments in addition to further detailed research of mechanisms for the DWCs-induced increase in CO₂ releases among various soils all over the world.