show Abstracthide AbstractThe cultivation areas of Gracilariopsis lemaneiformis in Nanao Island of Guangdong Province were selected as research sites, and Gracilariopsis lemaneiformis and seawater samples were collected. The diversity of diazotrophs communities, nitrogenase activity, and the abundance of nifH gene associated with G. lemaneiformis and seawater in different cultivation periods were analyzed by using acetylene reduction, qPCR, and nifH gene high throughput sequencing technology, and the nitrogen fixations of diazotrophs under different environment conditions were investigated.