Nitrifiers Cooperate to Produce Nitrous Oxide in Plateau Wetland Sediments

Abstract

The thawing of dormant plateau permafrost emits nitrous oxide (N₂O) through wetlands; however, the N₂O production mechanism in plateau wetlands is still unclear. Here, we used the ¹⁵N-¹⁸O double tracer technique and metagenomic sequencing to analyze the N₂O production mechanism in the Yunnan-Kweichow and Qinghai-Tibet plateau wetlands during the summer of 2020. N₂O production activity was detected in all 16 sediment samples (elevation 1020-4601 m: 2.55 ± 0.42-26.38 ± 3.25 ng N g^-1 d^-1) and was promoted by nitrifier denitrification (ND). The key functional genes of ND (<i>amo</i>A, <i>hao</i>, and <i>nir</i>K) belonged to complete ammonia oxidizing (comammox) bacteria, and the key ND species was the comammox bacterium <i>Nitrospira nitrificans</i>. We found that the comammox bacterial species <i>N. nitrificans</i> and the ammonia oxidizing bacterial (AOB) species <i>Nitrosomonas europaea</i> cooperate to produce N₂O in the plateau wetland sediments. Furthermore, we inferred that environmental factors (elevation and total organic matter (TOM)) influence the cooperation pattern via <i>N. nitrificans</i>, thus affecting the N₂O production activity in the plateau wetland sediments. Our findings advance the mechanistic understanding of nitrifiers in biogeochemical cycles and global climate change.