Skau Lars Fredrik, Andersen Tom, Thrane Jan-Erik, Hessen Dag Olav
Department of Bioscience, University of Oslo, Oslo, Norway.
Norwegian Institute for Water Research, Oslo, Norway.
PeerJ. 2017 Sep 5;5:e3743. doi: 10.7717/peerj.3743. eCollection 2017.
Temperature and nutrients are key factors affecting the growth, cell size, and physiology of marine phytoplankton. In the ocean, temperature and nutrient availability often co-vary because temperature drives vertical stratification, which further controls nutrient upwelling. This makes it difficult to disentangle the effects of temperature and nutrients on phytoplankton purely from observational studies. In this study, we carried out a factorial experiment crossing two temperatures (13°and 19°C) with two growth regimes (P-limited, semi-continuous batch cultures ["-P"] and nutrient replete batch cultures in turbidostat mode ["+P"]) for three species of common marine haptophytes () to address the effects of temperature and nutrient limitation on elemental content and stoichiometry (C:N:P), total RNA, cell size, and growth rate. We found that the main gradient in elemental content and RNA largely was related to nutrient regime and the resulting differences in growth rate and degree of P-limitation, and observed reduced cell volume-specific content of P and RNA (but also N and C in most cases) and higher N:P and C:P in the slow growing -P cultures compared to the fast growing +P cultures. P-limited cells also tended to be larger than nutrient replete cells. Contrary to other recent studies, we found lower N:P and C:P ratios at high temperature. Overall, elemental content and RNA increased with temperature, especially in the nutrient replete cultures. Notably, however, temperature had a weaker-and in some cases a negative-effect on elemental content and RNA under P-limitation. This interaction indicates that the effect of temperature on cellular composition may differ between nutrient replete and nutrient limited conditions, where cellular uptake and storage of excess nutrients may overshadow changes in resource allocation among the non-storage fractions of biomass (e.g. P-rich ribosomes and N-rich proteins). Cell size decreased at high temperature, which is in accordance with general observations.
温度和营养物质是影响海洋浮游植物生长、细胞大小和生理特性的关键因素。在海洋中，温度和营养物质的可利用性常常共同变化，因为温度驱动垂直分层，进而控制营养物质的上升流。这使得仅从观测研究中难以厘清温度和营养物质对浮游植物的影响。在本研究中，我们进行了一项析因实验，将两种温度（13°C和19°C）与两种生长模式（磷限制，半连续分批培养["-P"]和在恒浊器模式下营养充足的分批培养["+P"]）进行交叉，用于三种常见海洋定鞭藻，以探讨温度和营养限制对元素含量和化学计量比（C:N:P）、总RNA、细胞大小和生长速率的影响。我们发现，元素含量和RNA的主要梯度在很大程度上与营养模式以及由此产生的生长速率和磷限制程度的差异有关，并且观察到与快速生长的+P培养物相比，生长缓慢的-P培养物中磷和RNA的细胞体积比含量降低（但在大多数情况下氮和碳也是如此），氮磷比和碳磷比更高。磷限制的细胞也往往比营养充足的细胞更大。与其他近期研究相反，我们发现在高温下氮磷比和碳磷比更低。总体而言，元素含量和RNA随温度升高而增加，尤其是在营养充足的培养物中。然而，值得注意的是，在磷限制条件下，温度对元素含量和RNA的影响较弱，在某些情况下甚至有负面影响。这种相互作用表明，温度对细胞组成的影响在营养充足和营养限制条件下可能不同，在营养充足条件下，细胞对过量营养物质的吸收和储存可能掩盖了生物量非储存部分（如富含磷的核糖体和富含氮的蛋白质）之间资源分配的变化。细胞大小在高温下减小，这与一般观察结果一致。
