Isotopic assessment of CO sub(2) production through soil organic matter decomposition in the tropics

• Published in: Nutrient cycling in agroecosystems 2005-01, Vol.71 (1), p.109-116
• Main Authors: Ueda, Shingo, Go, Chun-Sim U, Ishizuka, Shigehiro, Tsuruta, Haruo, Iswandi, Anas, Murdiyarso, Daniel
• Format: Article
• Language: English
• ISSN: 1385-1314; 1573-0867
• DOI: 10.1007/s10705-004-1197-8

Values of delta super(13)C and delta super(15)N 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 CO sub(2) production. The delta super(13)C and delta super(15)N values of SOM increased with depth in the 0-30 cm layer in the preserved forest, reflecting super(13)C and super(15)N 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 delta super(15)N than in super(13)C at all sites in Pasir Mayang. The delta super(13)C -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 super(13)C value than the original SOM. However, the delta super(15)N-SOM profiles before and after such a drastic event did not change appreciably. The delta super(15)N-SOM became higher as the C/N ratio decreased and as soil sugar content decreased. These observations suggest that delta super(15)N-SOM is a variable that changes with the amount of easily decomposable organic matter (EDOM) in soil. Soil incubation experiments demonstrated a correlation between CO sub(2) production rate and degree of vertical super(15)N-enrichment in SOM, which was applied to field data to estimate CO sub(2) 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, CO sub(2) production through SOM decomposition controlled 70 of variation in CO sub(2) emission among the locations. In the remaining 22 locations, however, the CO sub(2) emission was neither related to CO sub(2) 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 CO sub(2) emission in these sites.