Long-term water regime differentiates changes in decomposition and microbial properties in tropical peat soils exposed to the short-term drought

Tropical peatlands function as substantial carbon sinks, but are susceptible to the impact of global climate changes (especially drought) and drainage. The effects of drought and drainage on tropical peatlands have been investigated separately, but the combined effects of these 2 factors have not been examined in depth. To understand how tropical peat soils are decomposed by a short-term drought event differently with drainage history (pristine, intermediate, and drained), we collected peat soils from 3sites with distinct water regimes and performed a 28-day dry incubation. We found that the activities of 5 hydrolase enzymes decreased significantly at all sites, but those of 2 oxidase enzymes increased after the incubation. In conjunction with these alterations in extracellular enzyme activities, peat soil from a high water regime (pristine) released dissolved organic carbon (DOC) with high aromaticity, while that from a low water regime (intermediate and drained) released labile forms of DOC. This implies the initial quality and composition of peat soil, which is caused by the long-term water regime, influence the form of DOC released under drought conditions. Microbial (bacteria, archaea, and fungi) community structures of all sites shifted significantly during the drought incubation, and bacterial and fungal community structures in the soil from the high water regime were distinct even after the drought event, indicating they are more resistant to drastic hydrological changes. Gene copy numbers of bacteria and archaea decreased significantly, but that of fungi in soil with the low water regime increased considerably after the drought incubation. The increased fungal abundance in soils from sites with a low water table could partially explain the larger amount of carbon dioxide released from these soils. Overall, peat soil from sites with low water tables released large amounts of carbon dioxide, methane and dissolved carbon, and the microbial community structure at these sites was more affected by the drought incubation. These results suggest that the lowered water level in tropical peatlands is more vulnerable to drought event and will release more amounts of CO2, CH4, and DOC compared to pristine peatlands as a result of differences in enhanced oxidative enzyme activities, and microbial respiration of which varied with the long-term water regime history. ► We incubated Indonesian peat soils with different water levels to simulate the short-term drough