Fluxes of CO_2, N_2O and CH_4 by ^<222>Rn and chamber methods in cold-temperate grassland soil, northern Japan(<Special Section>Soil and plant aspects in the Integrated Land Ecosystem-Atmosphere Processes Study (iLEAPS))

This study conducted flux measurements of carbon dioxide (CO_2), nitrous oxide (N_2O) and methane (CH_4), estimated by ^<222>Rn (Radon) and chamber methods in a cold-temperate northern Japanese grassland soil during summer and winter seasons. Our research aims to compare these fluxes of CO_2, N_2O and CH_4 calculated by ^<222>Rn and static chamber methods, and to understand the responses of fluxes by ^<222>Rn and chamber methods to temperature. ^<222>Rn fluxes ranged from 0.0046 to 0.0157 Bq m^2 s^<-1>, and the average was 0.0068 ± 0.0013 Bq m^2 s^<-1> on sandy soil (> 50% sand). The average diffusion coefficients for CO_2, N_2O and CH_4 calculated using the ^<222>Rn method were 0.049 ± 0.008 cm^2 s^<-1>, 0.023 ± 0.005 cm^2 s^<-1> and 0.054 ± 0.008 cm^2 s^<-1>, respectively, reflecting seasonality. CO_2, N_2O and CH_4 flux measurements from the ^<222>Rn method were in good agreement with those of the static chamber method, within the observed range of error, suggesting a high correlation coefficient of > 89% between the methods. Also, the temperatures of air and soil at 5-cm depth played a significant role in determining the fluxes of CO_2 and CH_4 measured by the ^<222>Rn and chamber methods; meanwhile, the N_2O flux displayed an inverse exponential relation to temperature. This suggests that N_2O flux may be regulated by other factors such as soil water content and soil oxygen concentration. The contribution of winter fluxes of CO_2, N2_O and CH_4 corresponded to 9, 51 and 3% of the annual fluxes of CO_2, N2_O and CH_4, respectively, reflecting higher winter N_2O production due to the constraint of oxygen in soil.