Table_1_Forest zone and root compartments outweigh long-term nutrient enrichment in structuring arid mangrove root microbiomes.docx

Mangroves offer many important ecosystem services including carbon sequestration, serving as nursery grounds to many organisms, and acting as barriers where land and sea converge. Mangroves exhibit environmental flexibility and resilience and frequently occur in nutrient-limited systems. Despite existing research on mangrove microbiomes, the effects of nutrient additions on microbial community structure, composition, and function in intertidal and landward zones of mangrove ecosystems remain unclear. We utilized a long-term nutrient amendment study in Exmouth Gulf, Western Australia conducted in two zones, the intertidal fringe and supralittoral scrub forests, dominated by Avicennia marina. Root samples were fractionated into rhizosphere, rhizoplane and endosphere compartments and analyzed by 16S rRNA gene amplicon sequencing to determine the effects of nutrient stress on community structure and function. Our data showed species richness and evenness were significantly higher in the scrub forest zone. PERMANOVA analysis revealed a significant effect of nutrient enrichment on beta diversity (p = 0.022, R2 = 0.012) in the fringe forest zone only. Cylindrospermopsis, which has been associated with harmful algal blooms, was found to be significantly enriched in fringe phosphate-fertilized plots and nitrogen-fixing Hyphomicrobiales were significantly depleted in the scrub nitrogen-fertilized plots. Meanwhile, root compartments and forest zone had a greater effect on beta diversity (p = 0.001, R2 = 0.186; p = 0.001, R2 = 0.055, respectively) than nutrient enrichment, with a significant interaction between forest zone and root compartment (p = 0.001, R2 = 0.025). This interaction was further observed in the distinct divergence identified in degradative processes of the rhizosphere compartment between the two forest zones. Degradation of aromatic compounds were significantly enriched in the fringe rhizosphere, in contrast to the scrub rhizosphere, where degradation of carbohydrates was most significant. Despite the highly significant effect of forest zone and root compartments, the long-term effect of nutrient enrichment impacted community structure and function, and potentially compromised overall mangrove health and ecosystem stability.

红树林（Mangroves）具备多项重要的生态系统服务功能，包括碳固存（carbon sequestration）、为众多生物提供育苗场所以及作为陆海交汇地带的防护屏障。红树林具有环境适应性与恢复力，且常生长于营养受限的生境中。尽管已有针对红树林微生物组（microbiomes）的相关研究，但养分添加对红树林生态系统潮间带（intertidal）及向陆带（landward zones）微生物群落结构、组成与功能的影响仍不明确。本研究依托澳大利亚西部埃克斯茅斯湾的长期养分添加实验，实验设置了以白骨壤（Avicennia marina）为优势种的两个生境带：潮间带边缘带与潮上带灌丛林带。研究将根系样品分为根际（rhizosphere）、根面（rhizoplane）与内生境（endosphere）三个生境分区，通过16S rRNA基因扩增子测序（16S rRNA gene amplicon sequencing）技术进行分析，以探究养分胁迫对微生物群落结构与功能的影响。研究数据显示，灌丛林带的物种丰富度与均匀度均显著更高。置换多元方差分析（PERMANOVA）结果显示，仅在潮间带边缘带中，养分富集对β多样性存在显著影响（p=0.022，R²=0.012）。与有害藻华密切相关的柱胞藻属（Cylindrospermopsis）在潮间带边缘带的磷施肥样地中显著富集；而灌丛林带氮施肥样地内的固氮生丝微菌目（Hyphomicrobiales）则显著减少。与此同时，根系生境分区与林带类型对β多样性的影响（分别为p=0.001，R²=0.186；p=0.001，R²=0.055）均大于养分富集，且林带类型与根系生境分区之间存在显著的交互效应（p=0.001，R²=0.025）。该交互效应还体现在两个林带的根际生境降解过程存在显著差异：潮间带边缘带根际的芳香族化合物降解功能显著富集，而灌丛林带根际则以碳水化合物降解功能最为显著。尽管林带类型与根系生境分区的影响极为显著，但长期养分富集仍会改变微生物群落结构与功能，或会损害红树林整体健康与生态系统稳定性。