As important links between marine and terrestrial ecosystems, seabirds have profound effects on island ecosystems, especially by their phosphorus and nitrogen inputting. However, comprehensively understandings of how seabird nesting affect island soil ecosystem and its mechanisms are still unclear. Here, the responding of soil microbial communities in biodiversity and functions to the changing soil properties induced by seabird nesting were investigated based on a case study on a subtropical, unpopulated island of China. Kinds of soil physicochemical properties, soil enzymatic activities, and the biodiversity and functional genes of soil microbial communities were analyzed. Results showed that seabird nesting drastically altered the soil physicochemical properties, especially intensive phosphorus input. Soil nitrate nitrogen was also significantly increased, while ammonium nitrogen was notably decreased. Seabird nesting decreased the alpha diversity of soil microbial communities and led to a more frangible bacterial co-occurrence network. The relative abundances of Acidobacteriota and Proteobacteria were significantly increased, while that of Chloroflexi was significantly reduced. Soil biogeochemical cycles might also be weakened via the inhibition of functional genes involved in carbon fixation in photosynthetic organisms, nitrogen fixation etcetera, and the activity declination of soil β-glucosidase, urease, acid phosphatase and aryl sulfatase. It is more likely that the seabird-induced variations in soil physicochemical properties caused the reduction of soil enzymatic activities, and the intensive phosphorus was further identified as the key driver of seabird nesting shifting island soil ecosystems. These findings provide a deeper understanding of how seabird nesting impact island soil ecosystems and its possible mechanisms.

Microbial functional genes; Phosphorus input; Seabird guano; Soil enzymes; Soil nitrogen