Scientists from the Institute of Applied Ecology of the Chinese Academy of Sciences have developed an automated monitoring system to continuously track methane absorption by forest soils. A four-year study at a temperate forest site revealed a strong correlation between soil temperature, moisture, and methane uptake rates, enhancing understanding of methane oxidation dynamics.
Methane (CH4) is a potent greenhouse gas with a global warming potential 28 to 34 times greater than carbon dioxide (CO2) over a century. Forest soils serve as a major biological sink for atmospheric methane, naturally removing it through a process called methane oxidation. This process is carried out by methanotrophic bacteria in the soil, which utilize methane as an energy source.
Traditional methods of measuring methane uptake, often involving infrequent manual sampling, may not capture the rapid changes in environmental conditions such as rainfall, limiting the ability to fully capture how soil temperature and moisture affect methanotrophic activity.
To overcome this, the researchers led by Professor FANG Yunting established an automated monitoring system at the Qingyuan National Forest Ecosystem Research Station, conducting continuous measurements over four years.
The study, published in the journal Agricultural and Forest Meteorology, showed that the forest soil consistently acted as a methane sink, absorbing an average of 5.24 kilograms of methane-carbon per hectare per year. The rate of methane absorption varied seasonally, peaking in the summer at 244 micrograms of carbon per square meter per hour and decreasing to a low of 0.8 micrograms of carbon per square meter per hour in the winter.
Analysis show that methane absorption in these soils is primarily controlled by soil temperature and moisture. While the abundance of methane-oxidizing bacteria and soil organic carbon also play a role, simple linear regression models showed that soil temperature alone explained 36% of the variability in methane uptake, and soil moisture accounted for 56%. A dual-factor model considering both temperature and water-filled pore space (Temp-WFPS) explained 86% of the annual variation in methane uptake.
The researchers also found that traditional monthly sampling can bias annual methane absorption by up to 19%. The high-frequency monitoring provides detailed daily, seasonal, and annual measurements of methane absorption and its response to changing environmental factors, offering valuable insights into the regulatory mechanisms of soil temperature and moisture on methane uptake.
This advancement aids the refinement of biogeochemical models and improves global methane budget estimates, providing essential knowledge for climate change mitigation efforts.
Seasonal variations in atmospheric and soil temperature, soil moisture and daily precipitation, and soil methane uptake (Image by LIU Yuqi)
