Endres Sonja, Galgani Luisa, Riebesell Ulf, Schulz Kai-Georg, Engel Anja
Biological Oceanography, GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany; Polar Biological Oceanography, Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI), Bremerhaven, Germany.
Biological Oceanography, GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany.
PLoS One. 2014 Jun 18;9(6):e99228. doi: 10.1371/journal.pone.0099228. eCollection 2014.
Marine bacteria are the main consumers of freshly produced organic matter. Many enzymatic processes involved in the bacterial digestion of organic compounds were shown to be pH sensitive in previous studies. Due to the continuous rise in atmospheric CO2 concentration, seawater pH is presently decreasing at a rate unprecedented during the last 300 million years but the consequences for microbial physiology, organic matter cycling and marine biogeochemistry are still unresolved. We studied the effects of elevated seawater pCO2 on a natural plankton community during a large-scale mesocosm study in a Norwegian fjord. Nine Kiel Off-Shore Mesocosms for Future Ocean Simulations (KOSMOS) were adjusted to different pCO2 levels ranging initially from ca. 280 to 3000 µatm and sampled every second day for 34 days. The first phytoplankton bloom developed around day 5. On day 14, inorganic nutrients were added to the enclosed, nutrient-poor waters to stimulate a second phytoplankton bloom, which occurred around day 20. Our results indicate that marine bacteria benefit directly and indirectly from decreasing seawater pH. During the first phytoplankton bloom, 5-10% more transparent exopolymer particles were formed in the high pCO2 mesocosms. Simultaneously, the efficiency of the protein-degrading enzyme leucine aminopeptidase increased with decreasing pH resulting in up to three times higher values in the highest pCO2/lowest pH mesocosm compared to the controls. In general, total and cell-specific aminopeptidase activities were elevated under low pH conditions. The combination of enhanced enzymatic hydrolysis of organic matter and increased availability of gel particles as substrate supported up to 28% higher bacterial abundance in the high pCO2 treatments. We conclude that ocean acidification has the potential to stimulate the bacterial community and facilitate the microbial recycling of freshly produced organic matter, thus strengthening the role of the microbial loop in the surface ocean.
海洋细菌是新产生的有机物质的主要消费者。在先前的研究中，许多参与细菌消化有机化合物的酶促过程被证明对pH敏感。由于大气中二氧化碳浓度持续上升，目前海水pH值正以过去3亿年中前所未有的速度下降，但对微生物生理学、有机物质循环和海洋生物地球化学的影响仍未得到解决。在挪威峡湾进行的一项大规模中尺度实验研究中，我们研究了海水pCO2升高对自然浮游生物群落的影响。九个用于未来海洋模拟的基尔近海中尺度实验舱（KOSMOS）被调节到不同的pCO2水平，初始范围约为280至3000微大气压，并在34天内每隔一天进行采样。第一次浮游植物水华在第5天左右出现。在第14天，向封闭的、营养贫乏的水体中添加无机养分，以刺激第二次浮游植物水华，第二次水华在第20天左右出现。我们的结果表明，海洋细菌直接或间接地受益于海水pH值的降低。在第一次浮游植物水华期间，高pCO2中尺度实验舱中形成的透明胞外聚合物颗粒多5%-10%。同时，蛋白质降解酶亮氨酸氨肽酶的效率随着pH值的降低而增加，与对照相比，在最高pCO2/最低pH值的中尺度实验舱中该酶活性高达三倍。总体而言，在低pH条件下，总氨肽酶活性和细胞特异性氨肽酶活性均有所提高。有机质酶促水解增强与凝胶颗粒作为底物的可利用性增加相结合，使得高pCO2处理中的细菌丰度提高了28%。我们得出结论，海洋酸化有可能刺激细菌群落，并促进新产生的有机物质的微生物循环，从而加强微生物环在海洋表层的作用。
