Plant microbiomes are shaped by forces working at different spatial scales. Environmental factors determine a pool of potential symbionts while host physiochemical factors influence how those microbes associate with distinct plant tissues. These scales are seldom considered simultaneously, despite their potential to interact. Here, we analyze epiphytic microbes from nine Hibiscus tiliaceus trees across a steep, but short, environmental gradient within a single Hawaiian watershed. At each location, we sampled eight microhabitats: leaves, petioles, axils, stems, roots, and litter from the plant, as well as surrounding air and soil. The composition of bacterial communities is better explained by microhabitat, while location better predicted compositional variance for fungi. Fungal community compositional dissimilarity increased more rapidly along the gradient than did bacterial composition. Additionally, the rates of fungal community compositional dissimilarity along the gradient differed among plant parts, and these differences influenced the distribution patterns and range size of individual taxa. Within plants, microbes were compositionally nested such that aboveground communities contained a subset of the diversity found belowground. Our findings indicate that both environmental context and microhabitat contribute to microbial compositional variance in our study, but that these contributions are influenced by the domain of microbe and the specific microhabitat in question, suggesting a complicated and potentially interacting dynamic.

植物微生物组是由在不同空间尺度上起作用的力形成的。环境因素决定了潜在共生体的数量，而宿主的生理化学因素会影响这些微生物与不同植物组织的结合方式。这些尺度很少被同时考虑，尽管它们有可能相互作用。在这里，我们分析了 9种 Hibiscus tiliaceus的附生微生物夏威夷单一流域内陡峭但较短的环境梯度上的树木。在每个位置，我们对八个微生境进行了采样：叶子、叶柄、叶腋、茎、根和植物的凋落物，以及周围的空气和土壤。微生境可以更好地解释细菌群落的组成，而位置可以更好地预测真菌的组成差异。与细菌组成相比，真菌群落组成差异沿梯度增加得更快。此外，沿梯度的真菌群落组成差异率在植物各部分之间存在差异，这些差异影响了个体分类群的分布模式和范围大小。在植物中，微生物在组成上嵌套，使得地上群落包含地下多样性的一个子集。我们的研究结果表明，在我们的研究中，环境背景和微生境都会导致微生物组成的变化，但这些贡献受到微生物领域和所讨论的特定微生境的影响，表明存在复杂且可能相互作用的动态。