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 shaping soil bacteria and fungi patterns. By contrast, we found
little evidence for the role of spatial processes (i.e., dispersal
limitation or soil heterogeneity) within the island. Overall, this study
highlights the importance of dissecting potential mechanisms underlying
multi-trophic community dynamics to explain patterns of biodiversity and
its variation on islands.

尽管岛屿上的正物种-面积关系（species-area relationship）常被观测到，但支撑这一规律的潜在机制仍鲜有深入研究。本研究通过分析热带群岛内不同空间尺度下的岛屿群落多样性及其岛内土壤属性，探究了该群岛植物、伴生土壤细菌与真菌的岛屿物种-面积关系背后的潜在机制。研究发现，植物与土壤微生物群落在不同尺度下均呈现出相似的正物种-面积关系，且大岛更高的分类多样性主要由样本内更高的物种丰富度所驱动。上述格局主要源于随岛屿面积变化的生境质量差异，而非通常归因于物种-面积关系的空间过程。具体而言，土壤全磷含量随岛屿面积的变化对植物群落格局的解释力最强，而土壤pH值的变化则是塑造土壤细菌与真菌分布格局的最关键因素。相较之下，本研究几乎未发现岛屿内空间过程（即扩散限制或土壤异质性）发挥作用的证据。总体而言，本研究强调了拆解多营养级群落动态背后的潜在机制，对于阐释岛屿生物多样性格局及其变异规律的重要意义。