The cultivation of macroalgae in China accounts for 70% of the world, and the cultivation area reaches 129,000 hectares. The seaweed primary production acts as a strong driver of production in the coastal ocean and has been called for its inclusion in the blue carbon. On the other hand, the decomposition of drift algae promotes anoxic conditions by providing organic carbon sources and the organics stimulate microbial heterotrophic NO₃^- turnover simultaneously. In addition, statistically, the number of bacteria on the surface of dead algae was approximately twice of healthy algae. In macroalgae farming, before and after each algal was harvested, what are the N₂O production rate and the associated microbial community structure change in sediments with sedimentation of some macroalgae which hampers the understanding of net climatic effects of seaweed farming.

In this study, we plan to choose different seaweed farms in the north and the south of China as the study sites, by nitrogen isotope tracer method determination of sedimentary N₂O production rate in the core culture zones and outside reference zones, accompanied with the related microbial community and key genes expression. We aim to clarify the contribution of macroalgae farming to global climate change.

The expecting results are: 1) The contents of nutrient, N₂O and nitrogen gas in sediment of the cultivation area results were significant different before and after algal harvest in the northern and southern regions; 2) N₂O production enhances after algal harvesting; 3) There were significant differences in the rate of N₂O production by bacteria in sediments from different breeding areas, but both are mainly denitrification, and the microbial communities were also different.