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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 (RRHI), from soil organic matter (RSOM), and from litter (RL) to CO2 emissions from the forest floor (soil respiration; RS) 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 (δRHI), litter (δL) and SOM (δSOM) in the surface soil were −28.9, −30.1 and −24.3‰, respectively. This means that the differences between δSOM and δRHI are large enough to calculate the contributions of RRHI, RSOM and RL to RS based on the mass balance of the CO2 isotope ratios. RRHI and RSOM had close relationships with soil temperature, and RL was influenced by soil temperature and moisture. In summer, under high soil temperatures, RRHI and RSOM were the predominant sources of RS and the proportion of RRHI to RSOM to RL was 51:44:5. In winter, RL was predominant and the proportion of RRHI to RSOM to RL was 20:11:69. The estimated annual emissions of RRHI, RSOM and RL were 1.45, 2.10 and 1.30 Mg C ha−1, respectively; thus, the proportion of RRHI to RSOM to RL was 30:43:27 on a whole-year basis.