Global warming and acidification, induced by a substantial
increase
in anthropogenic CO2 emissions, are expected to have profound
impacts on biogeochemical cycles. However, underlying mechanisms of
nitrous oxide (N2O) production in estuarine and coastal
sediments remain rarely constrained under warming and acidification.
Here, the responses of sediment N2O production pathways
to warming and acidification were examined using a series of anoxic
incubation experiments. Denitrification and N2O production
were largely stimulated by the warming, while N2O 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 N2O production by
26 ± 4%, which was mainly attributed to the decline of the N2O yield by fungal denitrification. Fungal denitrification
was mainly responsible for N2O production under the warming
condition, while bacterial denitrification predominated N2O production under the acidification condition. The reduced site
preference of N2O under acidification reflects that the
dominant pathways of N2O production were likely shifted
from fungal to bacterial denitrification. In addition, acidification
decreased the diversity and abundance of nirS-type
denitrifiers, which were the keystone taxa mediating the low N2O production. Collectively, acidification can decrease sediment
N2O yield through shifting the responsible production pathways,
partly counteracting the warming-induced increase in N2O emissions, further reducing the positive climate warming feedback
loop.