Raut Yubin, Barr Casey R, Paris Emily R, Kapili Bennett J, Dekas Anne E, Capone Douglas G
Marine and Environmental Biology, University of Southern California, Los Angeles, CA, United States.
Earth System Science, Stanford University, Stanford, CA, United States.
Front Microbiol. 2024 Jan 5;14:1312843. doi: 10.3389/fmicb.2023.1312843. eCollection 2023.
Macroalgae, commonly known as seaweed, are foundational species in coastal ecosystems and contribute significantly to coastal primary production globally. However, the impact of macroalgal decomposition on benthic biological nitrogen fixation (BNF) after deposition to the seafloor remains largely unexplored. In this study, we measure BNF rates at three different sites at the Big Fisherman's Cove on Santa Catalina Island, CA, USA, which is representative of globally distributed rocky bottom macroalgal habitats. Unamended BNF rates varied among sites (0.001-0.05 nmol N g h ) and were generally within the lower end of previously reported ranges. We hypothesized that the differences in BNF between sites were linked to the availability of organic matter. Indeed, additions of glucose, a labile carbon source, resulted in 2-3 orders of magnitude stimulation of BNF rates in bottle incubations of sediment from all sites. To assess the impact of complex, autochthonous organic matter, we simulated macroalgal deposition and remineralization with additions of brown (i.e., and ), green (i.e., ), and red (i.e., ) macroalgae. While brown and green macroalgal amendments resulted in 53- to 520-fold stimulation of BNF rates-comparable to the labile carbon addition-red alga was found to significantly inhibit BNF rates. Finally, we employed sequencing to characterize the diazotrophic community associated with macroalgal decomposition. We observed a distinct community shift in potential diazotrophs from primarily in the early stages of remineralization to a community dominated by (e.g., sulfate reducers), , and toward the latter phase of decomposition of brown, green, and red macroalgae. Notably, the -containing community associated with red macroalgal detritus was distinct from that of brown and green macroalgae. Our study suggests coastal benthic diazotrophs are limited by organic carbon and demonstrates a significant and phylum-specific effect of macroalgal loading on benthic microbial communities.
大型藻类，通常被称为海藻，是沿海生态系统的基础物种，对全球沿海初级生产有重大贡献。然而，大型藻类分解后沉积到海底对底栖生物固氮（BNF）的影响在很大程度上仍未得到探索。在本研究中，我们在美国加利福尼亚州圣卡塔利娜岛大渔人湾的三个不同地点测量了BNF速率，该地区代表了全球分布的岩石底部大型藻类栖息地。未添加物质时的BNF速率在不同地点有所不同（0.001 - 0.05 nmol N g h），且总体处于先前报道范围的下限。我们假设不同地点之间BNF的差异与有机物质的可用性有关。事实上，添加葡萄糖（一种易分解的碳源）导致所有地点沉积物的瓶内培养中BNF速率提高了2 - 3个数量级。为了评估复杂的本地有机物质的影响，我们通过添加褐藻（即 和 ）、绿藻（即 ）和红藻（即 ）来模拟大型藻类的沉积和再矿化。虽然褐藻和绿藻添加物导致BNF速率提高了53至520倍——与添加易分解碳源的效果相当——但发现红藻显著抑制BNF速率。最后，我们采用 测序来表征与大型藻类分解相关的固氮群落。我们观察到潜在固氮菌群落发生了明显变化，从再矿化早期主要的 转变为在褐藻、绿藻和红藻分解后期以 （如硫酸盐还原菌）、 和 为主的群落。值得注意的是，与红藻碎屑相关的含 群落与褐藻和绿藻的不同。我们的研究表明沿海底栖固氮菌受有机碳限制，并证明了大型藻类负荷对底栖微生物群落有显著的、特定门类的影响。
