Kelp Culture Enhances Coastal Biogeochemical Cycles by Maintaining Bacterioplankton Richness and Regulating Its Interactions.

As an important carbon sink, seaweed cultivation plays a vital role in controlling global climate change. However, most studies have been focused on the seaweed itself, and knowledge of bacterioplankton dynamics in seaweed cultivation activities is still limited. Here, a total of 80 water samples were obtained from a coastal kelp cultivation area and adjacent non-culture area in the seedling and mature stages. The bacterioplankton communities were analyzed using high-throughput sequencing of bacterial 16S rRNA genes, and the microbial genes involving biogeochemical cycles were measured by a high-throughput quantitative PCR (qPCR) chip. Seasonal variations in alpha diversity indices of bacterioplankton were found, and kelp cultivation mitigated this decline in biodiversity from the seedling to the mature stage. Further beta diversity and core taxa analyses revealed that the maintenance of biodiversity was due to kelp cultivation favoring the survival of rare bacteria. Comparisons of gene abundances between coastal water with and without kelp cultivation showed a more powerful capacity of biogeochemical cycles induced by kelp cultivation. More importantly, a positive relationship between bacterial richness and biogeochemical cycling functions was observed in samples with kelp cultivation. Finally, a co-occurrence network and pathway model indicated that the higher bacterioplankton biodiversity in kelp culture areas compared to non-mariculture regions could balance the microbial interactions to regulate biogeochemical cycles and thus enhance the ecosystem functions of kelp cultivation coasts. The findings of this study allow us to better understand the effects of kelp cultivation on coastal ecosystems and provide novel insights into the relationship between biodiversity and ecosystem functions.