Habitat quality drives the species-area relationship of plants and soil microbes in an ocean archipelago

While the positive species-area relationship on islands is frequently observed, the mechanisms underlying this pattern remain poorly studied. By analyzing insular community diversity across spatial scales and the soil properties within the islands, we were able to explore potential mechanisms leading to the island species-area relationship of plants, as well as associated soil bacteria and fungi, from a tropical archipelago. We found that both plant and soil microbial communities showed similar positive species-area relationships across scales and the greater taxonomic diversity on larger islands was mainly driven by the higher richness within samples. These patterns arose primarily due to shifting habitat quality with island area, rather than spatial processes generally attributed to species-area relationships. Specifically, for plants, changes in soil total phosphorus content with island area were most explanatory, while changes in soil pH appeared to play the most important role in s..., , , ReadMe for 'Habitat quality drives the species-area relationship of plants and microbes in an ocean archipelago'.

Our dataset was collected from the Paracel archipelago (i.e., Xisha islands, 15°46′ N to 17°08′ N and 111°11′ E to 112°54′ E) in the South China Sea. The Paracel archipelago comprises many small oceanic islands primarily made from coral and sand (Ye et al., 1985; Gong et al., 1996). The vegetation on these islands consists mainly of shrubs and herbs, with dominant plant species including Scaevola taccada, Guettarda speciosa, Tournefortia argentea and Morinda citrifolia.

Although there are ~30 islands in the Paracel archipelago, many of them are too small or lack vegetation to meet the requirements for field surveys. Thus, in April 2023, ten representative islands were selected with an area ranging from 2 to 40ha that were minimally disturbed by human activities. On each island, woody plants, together with soil bacteria and fungi, were sampled simultaneously.

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