We investigated the impact of kelp deposition on the geochemistry and microbial community composition of beach sands on the island of Helgoland (North Sea). The composition of the microbial community at a beach with regular kelp deposition appeared shaped by this regular input of organic material, as indicated by significantly higher proportions of aerobic degraders, fermenters, and sulfur cycling microorganisms. Rapid degradation of deposited kelp by this community leads to high levels of dissolved organic and inorganic carbon and nutrients, a lower pH and anoxia. Aerobic respiration, fermentation, Fe- and SO42- reduction and methanogenesis were strongly enhanced, with SO42- reduction being the main process in kelp degradation. SO42- reduction rates increased 20 to 25-fold upon addition of kelp. The main route of electrons from kelp to SO42- was not via CO and H2, as expected, but via organic fermentation products. O2 supply by the tides was not sufficient and reduced intermediates escaped from the sediment with tidal water retraction. The resulting extremely high levels of free sulfide (>10 mmol L-1) lead to abundant filamentous growth of sulfur-oxidizing bacteria largely composed of a rare O2-adapted Sulfurovum lacking the expected denitrification genes. Our results show that regular kelp deposition strongly enhances the thermodynamic disequilibrium in the beach sand habitat, leading to a dramatic enhancement of the sulfur cycle.

中文翻译：

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海带沉积改变了沙滩中的矿化途径和微生物群落

我们调查了海带沉积对黑尔戈兰岛（北海）海滩沙滩的地球化学和微生物群落组成的影响。有规律的海带沉积的海滩上的微生物群落组成似乎是由这种规律的有机物质输入所塑造的，如需氧降解剂、发酵罐和硫循环微生物的比例显着提高所表明的那样。该群落沉积的海带的快速降解导致高水平的溶解有机和无机碳和营养物质、较低的 pH 值和缺氧。有氧呼吸、发酵、Fe- 和 SO42- 还原和产甲烷作用显着增强，SO42- 还原是海带降解的主要过程。添加海带后，SO42- 减少率增加了 20 到 25 倍。正如预期的那样，从海带到 SO42- 的电子的主要途径不是通过 CO 和 H2，而是通过有机发酵产物。潮汐提供的 O2 供应不足，随着潮水退缩，还原的中间体从沉积物中逸出。由此产生的极高水平的游离硫化物（> 10 mmol L-1）导致硫氧化细菌的大量丝状生长，主要由缺乏预期的反硝化基因的稀有的 O2 适应 Sulfurovum 组成。我们的结果表明，常规海藻沉积强烈增强了海滩沙栖息地的热力学不平衡，导致硫循环的显着增强。由此产生的极高水平的游离硫化物（> 10 mmol L-1）导致硫氧化细菌的大量丝状生长，主要由缺乏预期的反硝化基因的稀有的 O2 适应 Sulfurovum 组成。我们的结果表明，常规海藻沉积强烈增强了海滩沙栖息地的热力学不平衡，导致硫循环的显着增强。由此产生的极高水平的游离硫化物（> 10 mmol L-1）导致硫氧化细菌的大量丝状生长，主要由缺乏预期的反硝化基因的稀有的 O2 适应 Sulfurovum 组成。我们的结果表明，常规海藻沉积强烈增强了海滩沙栖息地的热力学不平衡，导致硫循环的显着增强。