Separation of soil respiration into CO₂ emission sources using ¹³C natural abundance in a deciduous broad-leaved forest in Japan

Abstract

In determining the soil and ecosystem carbon balance, it is necessary to distinguish between autotrophic respiration and heterotrophic respiration. We attempted to measure the contribution of CO₂ emissions from plant roots (R_RHI), from soil organic matter (R_SOM), and from litter (R_L) to CO₂ emissions from the forest floor (soil respiration; R_S) in a deciduous forest of oak (Quercus serrata Thunb.) and hornbeams (Carpinus laxiflora Sieb. et Zucc. Bl., Carpinus tschonoskii Maxim. and Carpinus japonica Bl.) on Andosols in Japan, using a ¹³C natural abundance technique. The ¹³C natural abundances of roots (δ_RHI), litter (δ_L) and SOM (δ_SOM) in the surface soil were −28.9, −30.1 and −24.3‰, respectively. This means that the differences between δ_SOM and δ_RHI are large enough to calculate the contributions of R_RHI, R_SOM and R_L to R_S based on the mass balance of the CO₂ isotope ratios. R_RHI and R_SOM had close relationships with soil temperature, and R_L was influenced by soil temperature and moisture. In summer, under high soil temperatures, R_RHI and R_SOM were the predominant sources of R_S and the proportion of R_RHI to R_SOM to R_L was 51:44:5. In winter, R_L was predominant and the proportion of R_RHI to R_SOM to R_L was 20:11:69. The estimated annual emissions of R_RHI, R_SOM and R_L were 1.45, 2.10 and 1.30 Mg C ha⁻¹, respectively; thus, the proportion of R_RHI to R_SOM to R_L was 30:43:27 on a whole-year basis.

Key words:

• Andosols
• autotrophic respiration
• forest soil
• soil organic matter decomposition
• ¹³C stable isotope

ACKNOWLEDGMENTS

The authors wish to thank Drs N. Okada of Kyoto University and Y. Tsuboyama of the Forestry and Forest Products Research Institute for their help in the use and maintenance of the isotope analysis equipment. We appreciate being allowed to use the research site by the Ibaraki District Forest Office. This work was supported by research grant numbers 199903 and 200303 from the Forestry and Forest Products Research Institute, Japan.