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Using radiocarbon to estimate potential impacts of warming on soil carbon storage
-Toward a reliable prediction of feedback between climate change and global carbon cycle-
Oct. 21, 2008
Japan Atomic Energy Agency (JAEA) and Forestry and Forest Products Research Institute (FFPRI) have developed a radiocarbon-based approach to quantitatively understand heterogeneity in soil organic carbon (SOC) dynamics at Appi, a cool-temperate Japanese beech forest, and demonstrated that global warming can continue to accelerate carbon loss from slow-cycling SOC pools over the next century.
Soil stores twice as much carbon as the atmosphere and nearly triple the amount of carbon in terrestrial biomass. It is well documented that global warming can lead to accelerated microbial decomposition of SOC and enhance the release of CO2 from the soil to the atmosphere; however, the magnitude and timing of this effect remain highly uncertain due to a lack of quantitative data concerning the heterogeneity of SOC dynamics.
Using natural and �bomb� radiocarbon (produced by atmospheric weapons testing in the 1960s) as tracers of SOC dynamics on time scales of centuries to millennia and years to decades, respectively, we have estimated mean residence times (MRTs) of chemically fractionated soil samples, and succeeded in representing the Appi forest soil as a complex of six SOC pools with different MRT ranges. Moreover, the predicted response of the SOC pools to warming at a rate of 0.5 oC per decade reveals that slow-cycling SOC pools, which have MRTs of several decades to 200 years and account for about a half of total SOC stock, can potentially lead to an accelerated loss of SOC over the next century, and consequently provide the primary source of increase in CO2 release from the soil. The findings suggest that identifying the size and MRTs of the world�s slow-cycling pool soils is the key to a reliable evaluation of carbon cycle-climate feedback under global warming.
The present results are to be published in Global Change Biology.
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