Acidification Offset Warming-Induced Increase in NO Production in Estuarine and Coastal Sediments.

Global warming and acidification, induced by a substantial increase in anthropogenic CO emissions, are expected to have profound impacts on biogeochemical cycles. However, underlying mechanisms of nitrous oxide (NO) production in estuarine and coastal sediments remain rarely constrained under warming and acidification. Here, the responses of sediment NO production pathways to warming and acidification were examined using a series of anoxic incubation experiments. Denitrification and NO production were largely stimulated by the warming, while NO production decreased under the acidification as well as the denitrification rate and electron transfer efficiency. Compared to warming alone, the combination of warming and acidification decreased NO production by 26 ± 4%, which was mainly attributed to the decline of the NO yield by fungal denitrification. Fungal denitrification was mainly responsible for NO production under the warming condition, while bacterial denitrification predominated NO production under the acidification condition. The reduced site preference of NO under acidification reflects that the dominant pathways of NO production were likely shifted from fungal to bacterial denitrification. In addition, acidification decreased the diversity and abundance of -type denitrifiers, which were the keystone taxa mediating the low NO production. Collectively, acidification can decrease sediment NO yield through shifting the responsible production pathways, partly counteracting the warming-induced increase in NO emissions, further reducing the positive climate warming feedback loop.