Soil carbon dioxide emissions due to oxidative peat decomposition in an oil palm plantation on tropical peat.

Abstract Soil carbon dioxide (CO 2 ) efflux was measured continuously for two years using an automated chamber system in an oil palm plantation on tropical peat. This study investigated the factors controlling the CO 2 efflux and quantified the annual cumulative CO 2 emissions through soil respiration and heterotrophic respiration, which is equivalent to oxidative peat decomposition. Soil respiration was measured in close-to-tree ( 3 m, FT) plots, and heterotrophic respiration was measured in root-cut (RC) plots by a trenching method. The daily mean CO 2 efflux values (mean ± 1 standard deviation) were 2.80 ± 2.18, 1.59 ± 1.18, and 1.94 ± 1.58 μmol m −2  s −1 in the CT, FT, and RC plots, respectively. Daily mean CO 2 efflux increased exponentially as the groundwater level or water-filled pore space decreased, indicating that oxidative peat decomposition and gas diffusion in the soil increased due to enhanced aeration resulting from lower groundwater levels. Mean annual gap-filled CO 2 emissions were 1.03 ± 0.53, 0.59 ± 0.26, and 0.69 ± 0.21 kg C m −2 yr −1 in the CT, FT, and RC plots, respectively. Soil CO 2 emissions were significantly higher in the CT plots ( P   0.05), but did not differ significantly between the FT and RC plots. This implies that root respiration was negligible in the FT plots. Heterotrophic respiration accounted for 66% of soil respiration. Annual CO 2 emissions through both soil and heterotrophic respiration were smaller than those of other oil palm plantations on tropical peat, possibly due to the higher groundwater levels, land compaction, and continuous measurement of soil CO 2 efflux in this study. Mean annual total subsidence was 1.55 to 1.62 cm yr −1 , of which oxidative peat decomposition accounted for 72 to 74%. In conclusion, water management to raise groundwater levels would mitigate soil CO 2 emissions from oil palm plantations on tropical peatland.