Chandler Jeremy W, Lin Yajuan, Gainer P Jackson, Post Anton F, Johnson Zackary I, Zinser Erik R
Department of Microbiology, The University of Tennessee, M409 WLS, Knoxville, TN, 37966, USA.
Nicholas School of the Environment and Earth Sciences, Duke University, 135 Marine Lab Rd., Beaufort, NC, 28516, USA.
Environ Microbiol Rep. 2016 Apr;8(2):272-84. doi: 10.1111/1758-2229.12378. Epub 2016 Jan 28.
The vast majority of the phytoplankton communities in surface mixed layer of the oligotrophic ocean are numerically dominated by one of two ecotypes of Prochlorococcus, eMIT9312 or eMED4. In this study, we surveyed large latitudinal transects in the Atlantic and Pacific Ocean to determine if these ecotypes discretely partition the surface mixed layer niche, or if populations exist as a continuum along key environmental gradients, particularly temperature. Transitions of dominance occurred at approximately 19-21°C, with the eMED4 ecotype dominating the colder, and eMIT9312 ecotype dominating the warmer regions. Within these zones of regional dominance, however, the minority ecotype was not competed to extinction. Rather, a robust log-linear relationship between ecotype ratio and temperature characterized this stabilized coexistence: for every 2.5°C increase in temperature, the eMIT9312:eMED4 ratio increased by an order of magnitude. This relationship was observed in both quantitative polymerase chain reaction and in pyrosequencing assays. Water column stratification also contributed to the ecotype ratio along the basin-scale transects, but to a lesser extent. Finally, instances where the ratio of the eMED4 and eMIT9312 abundances did not correlate well with temperature were identified. Such occurrences are likely due to changes in water temperatures outpacing changes in community structure.
在贫营养海洋的表层混合层中，绝大多数浮游植物群落从数量上看是由原绿球藻的两种生态型之一主导，即eMIT9312或eMED4。在本研究中，我们在大西洋和太平洋进行了大范围的纬度断面调查，以确定这些生态型是否离散地划分了表层混合层生态位，或者种群是否沿着关键环境梯度（特别是温度）以连续体形式存在。优势转变发生在大约19 - 21°C，eMED4生态型在较冷区域占主导，而eMIT9312生态型在较暖区域占主导。然而，在这些区域优势区内，少数生态型并未被竞争至灭绝。相反，生态型比例与温度之间存在稳健的对数线性关系，这一关系表征了这种稳定的共存状态：温度每升高2.5°C，eMIT9312:eMED4比例就增加一个数量级。这种关系在定量聚合酶链反应和焦磷酸测序分析中均有观察到。水柱分层在沿盆地尺度断面的生态型比例中也有贡献，但程度较小。最后，我们识别出了eMED4和eMIT9312丰度比例与温度相关性不佳的情况。这种情况可能是由于水温变化速度超过了群落结构的变化速度。
