Extensive draining at tropical ombrotrophic peatlands in Southeast Asia has made these landscapes a global 'hot spots' for greenhouse gas emissions. Management practices and fires have changed substrate status, which affects microbial processes. Here, we present data on how change in management practices affect carbon (C) mineralization processes at these soils. We compared the C mineralization potentials of undrained swamp forest peat to those of abandoned peat (deforested, drained and burned peatlands in degraded condition) at various depths, with and without additional substrates (glucose, glutamate and nitrate), under oxic and anoxic conditions through ex situ experiments. Carbon mineralization (CO2 and CH4 production) rates were higher in the forest peat, with higher litter deposition and C availability. Production rates decreased with peat depth coinciding with decreasing availability of labile C. Consequently, the increase in production rates after labile substrate addition was relatively modest in forest peat as compared to the abandoned site and from the top layers as compared to deeper layers. Methanogenesis had little importance in total C loss. Adding labile C and nitrogen (N) enhanced heterotrophic CO2 production more than only addition of N. Surprisingly, oxygen availability did not limit CO2 production rates, but anoxic respiration also yielded substantial rates, especially at the forest peat. Flooding of these sites will therefore reduce, but not completely cease, peat C-loss. Reintroduced vegetation and fertilization in abandoned peatlands can enrich the peat with labile C and N compounds and thus lead to increased microbiological activity.
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