Enhanced viral production and virus-mediated mortality ofbacterioplankton in a natural iron-fertilized bloom eventabove theKerguelen Plateau

[摘要] Above the Kerguelen Plateau in the Southern Ocean natural iron fertilizationsustains a large phytoplankton bloom over 3 months during australsummer. During the KEOPS1 project (KErguelen Ocean and Plateau comparedStudy1) we sampled this phytoplankton bloom during its declining phase alongwith the surrounding high-nutrient–low-chlorophyll (HNLC) waters to study the effect of natural ironfertilization on the role of viruses in the microbial food web. Bacterialand viral abundances were 1.7 and 2.1 times, respectively, higher within thebloom than in HNLC waters. Viral production and virus-mediated mortality ofbacterioplankton were 4.1 and 4.9 times, respectively, higher in the bloom,while the fraction of infected cells (FIC) and the fraction of lysogeniccells (FLC) showed no significant differences between environments. Thepresent study suggests viruses to be more important for bacterial mortalitywithin the bloom and dominate over grazing of heterotrophic nanoflagellates(HNFs) during the late bloom phase. As a consequence, at least at a latebloom stage, viral lysis shunts part of the photosynthetically fixed carbonin iron-fertilized regions into the dissolved organic matter (DOM) pool withpotentially less particulate organic carbon transferred to larger members ofthe food web or exported.

[学科分类] 地球化学与岩石