Nutrient Cycling in Agroecosystems

, Volume 71, Issue 1, pp 109-116

Isotopic assessment of CO2 production through soil organic matter decomposition in the tropics

  • Shingo UedaAffiliated withCollege of Bioresource Sciences, Nihon University Email author 
  • , Chun-Sim U. GoAffiliated withCollege of Bioresource Sciences, Nihon University
  • , Shigehiro IshizukaAffiliated withForestry and Forest Product Research Institute
  • , Haruo TsurutaAffiliated withNational Institute for Agro-Environmental Sciences
  • , Anas IswandiAffiliated withDepartment of Soil Science, Bogor Agricultural University
  • , Daniel MurdiyarsoAffiliated withDepartment of Geophysics and Meteorology, Bogor Agricultural University

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Values of δ13C and δ15N of soil organic matter (SOM) under different land cover in Pasir Mayang, Jambi Province, Sumatra Island, Indonesia were examined to apply them as indicators of SOM dynamics and related CO2 production. The δ13C and δ15N values of SOM increased with depth in the 0–30 cm layer in the preserved forest, reflecting 13C and 15N richment in SOM through mineralization and immobilization. The degree of vertical enrichment, difference between 0–5 cm and 10–15 cm SOM, was more pronounced in δ15N than in 13C at all sites in Pasir Mayang. The δ13C -SOM profiles fluctuated through clear-cutting the forest and subsequent burning, which was due to input of biomass with higher C/N molar ratio and lower 13C value than the original SOM. However, the δ15N-SOM profiles before and after such a drastic event did not change appreciably. The δ15N-SOM became higher as the C/N ratio decreased and as soil sugar content decreased. These observations suggest that δ15N-SOM is a variable that changes with the amount of easily decomposable organic matter (EDOM) in soil. Soil incubation experiments demonstrated a correlation between CO2 production rate and degree of vertical 15N-enrichment in SOM, which was applied to field data to estimate CO2 production through SOM decomposition. A similar analysis was performed with the soils collected at 27 locations in other districts in Jambi Province than Pasir Mayang. In five locations covered by oil palm plantation, CO2 production through SOM decomposition controlled 70 of variation in CO2 emission among the locations. In the remaining 22 locations, however, the CO2 emission was neither related to CO2 production from SOM nor to ground litter amount. This observation indicated that mechanisms other than dead organic matter decomposition such as root respiration were dominant sources for CO2 emission in these sites.


C/N ratio δ13C δ15N Microbial respiration Soil CO2 emission Tropical soil