Drying and rewetting cycles amplify soil CO2 emissions

A research team led by Dr. Hirohiko Nagano and Ms. Yuri Suzuki from Niigata University, in collaboration with scientists from Kyushu University and the Japan Atomic Energy Agency, conducted a series of soil incubation experiments across ten forest and pastureland sites in Japan. Their findings reveal that repeated drying and rewetting cycles (DWCs), anticipated as a consequence of shifting precipitation patterns under climate change, substantially increase soil CO2 emissions.

The study demonstrated that CO2 release under DWCs was between 1.3 and 3.7 times higher compared to soils maintained at stable moisture levels. This increase coincided with a marked reduction in microbial biomass, suggesting that the destruction of microbial cells due to recurring DWCs led to a surge in newly available organic carbon, which fueled heightened microbial activity and CO2 release.

Moreover, the researchers observed that the rate of CO2 emission was significantly higher in soils rich in reactive metal-organic matter complexes. These complexes, traditionally viewed as stabilizers of soil organic carbon, appear to become more accessible to microbial degradation under repeated DWCs. Consequently, previously protected carbon reservoirs may transform into new sources of CO2 emissions under fluctuating moisture conditions.

Dr. Nagano emphasized the growing impact of extreme weather events driven by climate change and noted that this research provides valuable insights into how such events influence soil CO2 dynamics. "Our findings will contribute to refining predictive models for global carbon cycling and climate projections," he stated.

Moving forward, the research team aims to extend their studies beyond controlled laboratory settings to real-world environments. They plan to investigate the mechanisms behind DWCs-induced CO2 release in diverse soil types worldwide, with the goal of improving climate models and mitigation strategies.

Research Report:Comprehensive increase in CO2 release by drying-rewetting cycles among Japanese forests and pastureland soils and exploring predictors of increasing magnitude