小型浮游藻对海洋生态系统有巨大贡献,因为它们可通过光合作用来固定二氧化碳。对在夏季从北大西洋所取水样进行的一项新的研究表明,浮游藻类也消耗细菌,其细胞生物质的四分之一是通过“吃”浮游菌获得的。这一发现向认为浮游藻类完全依靠无机营养物的假设提出了挑战。
以前,专门化的原虫被认为是细菌的主要捕食者,但尽管小型藻消耗细菌的速度比较慢,它们的数量却非常大,以至于近表面海水中细菌消耗总量的40%至90%是由它们完成的。细菌消耗在一定程度上也许可解释为什么最小的藻类在海洋中占据支配地位。(生物谷Bioon.com)
生物谷推荐原始出处:
Nature 455, 224-226 (11 September 2008) | doi:10.1038/nature07236
High bacterivory by the smallest phytoplankton in the North Atlantic Ocean
Mikhail V. Zubkov1 & Glen A. Tarran2
National Oceanography Centre, Southampton, Hampshire SO14 3ZH, UK
Plymouth Marine Laboratory, Plymouth, Devon PL1 3DH, UK
Planktonic algae <5 m in size are major fixers of inorganic carbon in the ocean1. They dominate phytoplankton biomass in post-bloom, stratified oceanic temperate waters2. Traditionally, large and small algae are viewed as having a critical growth dependence on inorganic nutrients, which the latter can better acquire at lower ambient concentrations owing to their higher surface area to volume ratios3, 4. Nonetheless, recent phosphate tracer experiments in the oligotrophic ocean5 have suggested that small algae obtain inorganic phosphate indirectly, possibly through feeding on bacterioplankton. There have been numerous microscopy-based studies of algae feeding mixotrophically6, 7 in the laboratory8, 9, 10 and field11, 12, 13,14, as well as mathematical modelling of the ecological importance of mixotrophy15. However, because of methodological limitations16 there has not been a direct comparison of obligate heterotrophic and mixotrophic bacterivory. Here we present direct evidence that small algae carry out 40–95% of the bacterivory in the euphotic layer of the temperate North Atlantic Ocean in summer. A similar range of 37–70% was determined in the surface waters of the tropical North-East Atlantic Ocean, suggesting the global significance of mixotrophy. This finding reveals that even the smallest algae have less dependence on dissolved inorganic nutrients than previously thought, obtaining a quarter of their biomass from bacterivory. This has important implications for how we perceive nutrient acquisition and limitation of carbon-fixing protists as well as control of bacterioplankton in the ocean.