Thingstad T F, Bellerby R G J, Bratbak G, Børsheim K Y, Egge J K, Heldal M, Larsen A, Neill C, Nejstgaard J, Norland S, Sandaa R-A, Skjoldal E F, Tanaka T, Thyrhaug R, Töpper B
Department of Biology, University of Bergen, Jahnebakken 5PO Box 7800, 5020 Bergen, Norway.
Nature. 2008 Sep 18;455(7211):387-90. doi: 10.1038/nature07235. Epub 2008 Aug 20.
Predicting the ocean's role in the global carbon cycle requires an understanding of the stoichiometric coupling between carbon and growth-limiting elements in biogeochemical processes. A recent addition to such knowledge is that the carbon/nitrogen ratio of inorganic consumption and release of dissolved organic matter may increase in a high-CO(2) world. This will, however, yield a negative feedback on atmospheric CO(2) only if the extra organic material escapes mineralization within the photic zone. Here we show, in the context of an Arctic pelagic ecosystem, how the fate and effects of added degradable organic carbon depend critically on the state of the microbial food web. When bacterial growth rate was limited by mineral nutrients, extra organic carbon accumulated in the system. When bacteria were limited by organic carbon, however, addition of labile dissolved organic carbon reduced phytoplankton biomass and activity and also the rate at which total organic carbon accumulated, explained as the result of stimulated bacterial competition for mineral nutrients. This counterintuitive 'more organic carbon gives less organic carbon' effect was particularly pronounced in diatom-dominated systems where the carbon/mineral nutrient ratio in phytoplankton production was high. Our results highlight how descriptions of present and future states of the oceanic carbon cycle require detailed understanding of the stoichiometric coupling between carbon and growth-limiting mineral nutrients in both autotrophic and heterotrophic processes.
预测海洋在全球碳循环中的作用需要了解生物地球化学过程中碳与生长限制元素之间的化学计量耦合关系。此类知识的最新补充是，在高二氧化碳环境中，溶解有机物质无机消耗与释放的碳/氮比可能会增加。然而，只有当额外的有机物质在光合区内避免矿化时，这才会对大气中的二氧化碳产生负反馈。在此，我们展示了在北极远洋生态系统背景下，添加的可降解有机碳的归宿和影响如何关键地取决于微生物食物网的状态。当细菌生长速率受到矿质营养限制时，系统中会积累额外的有机碳。然而，当细菌受到有机碳限制时，添加易分解的溶解有机碳会降低浮游植物的生物量和活性，以及总有机碳积累的速率，这被解释为细菌对矿质营养竞争加剧的结果。这种违反直觉的“更多有机碳导致更少有机碳”效应在以硅藻为主的系统中尤为明显，在这些系统中浮游植物生产中的碳/矿质营养比很高。我们的结果强调了对海洋碳循环当前和未来状态的描述如何需要详细了解自养和异养过程中碳与生长限制矿质营养之间的化学计量耦合关系。
