Biology Department and.
Marine Policy Center, Woods Hole Oceanographic Institution, Woods Hole, MA 02543.
Proc Natl Acad Sci U S A. 2014 Jul 8;111(27):9852-7. doi: 10.1073/pnas.1321421111. Epub 2014 Jun 23.
Phytoplankton account for roughly half of global primary production; it is vital that we understand the processes that control their abundance. A key process is cell division. We have, however, been unable to estimate division rate in natural populations at the appropriate timescale (hours to days) for extended periods of time (months to years). For phytoplankton, the diel change in cell size distribution is related to division rate, which offers an avenue to obtain estimates from in situ observations. We show that a matrix population model, fit to hourly cell size distributions, accurately estimates division rates of both cultured and natural populations of Synechococcus. Application of the model to Synechococcus at the Martha's Vineyard Coastal Observatory provides an unprecedented view that reveals a distinct seasonality in division rates. This information allows us to separate the effects of growth and loss quantitatively over an entire seasonal cycle. We find that division and loss processes are tightly coupled throughout the year. The large seasonal changes in cell abundance are the result of periods of time (weeks to months) when there are small systematic differences that favor either net growth or loss. We also find that temperature plays a critical role in limiting division rate during the annual spring bloom. This approach opens a path to quantify the role of Synechococcus in ecological and biogeochemical processes in natural systems.
浮游植物约占全球初级生产力的一半；我们必须了解控制其丰度的过程，这一点至关重要。一个关键的过程是细胞分裂。然而，我们一直无法在适当的时间尺度（小时到天）和长时间（月到年）内估计自然种群的分裂率。对于浮游植物来说，细胞大小分布的昼夜变化与分裂率有关，这为从现场观测中获得估计值提供了一个途径。我们表明，一个适合每小时细胞大小分布的矩阵种群模型，可以准确估计培养和自然种群的聚球藻的分裂率。该模型在玛莎葡萄园海岸观测站对聚球藻的应用提供了一个前所未有的视角，揭示了分裂率的明显季节性。这些信息使我们能够在整个季节性周期内定量地分离生长和损失的影响。我们发现，分裂和损失过程全年都紧密耦合。细胞丰度的大季节性变化是由于存在有利于净生长或净损失的小系统差异的时间（数周至数月）。我们还发现，温度在整个年度春季水华期间限制分裂率方面起着关键作用。这种方法为量化在自然系统中聚球藻在生态和生物地球化学过程中的作用开辟了道路。
