Hessen Dag O, Hafslund Ola T, Andersen Tom, Broch Catharina, Shala Nita K, Wojewodzic Marcin W
Aquatic Ecology and Toxicology, Department of Biosciences, University of Oslo Oslo, Norway.
Front Microbiol. 2017 Jan 23;8:18. doi: 10.3389/fmicb.2017.00018. eCollection 2017.
Phytoplankton may respond both to elevated temperatures and reduced nutrients by changing their cellular stoichiometry and cell sizes. Since increased temperatures often cause increased thermal stratification and reduced vertical flux of nutrients into the mixed zone, it is difficult to disentangle these drivers in nature. In this study, we used a factorial design with high and low levels of phosphorus (P) and high and low temperature to assess responses in cellular stoichiometry, levels of RNA, and alkaline phosphatase activity (APA) in the chlorophyte Growth rate, C:P, C:N, N:P, RNA, and APA all responded primarily to P treatment, but except for N:P and APA, also temperature contributed significantly. For RNA, the contribution from temperature was particularly strong with higher cellular levels of RNA at low temperatures, suggesting a compensatory allocation to ribosomes to maintain protein synthesis and growth. These experiments suggest that although P-limitation is the major determinant of growth rate and cellular stoichiometry, there are pronounced effects of temperature also via interaction with P. At the ecosystem level, nutrients and temperature will thus interact, but temperatures would likely exert a stronger impact on these phytoplankton traits indirectly via its force on stratification regimes and vertical nutrient fluxes.
浮游植物可能会通过改变细胞化学计量比和细胞大小来应对温度升高和营养物质减少的情况。由于温度升高通常会导致热分层加剧，营养物质进入混合层的垂直通量减少，因此在自然环境中很难区分这些驱动因素。在本研究中，我们采用了析因设计，设置高磷和低磷以及高温和低温水平，以评估绿藻细胞化学计量比、RNA水平和碱性磷酸酶活性（APA）的响应情况。生长速率、碳磷比、碳氮比、氮磷比、RNA和APA主要对磷处理有响应，但除了氮磷比和APA外，温度也有显著影响。对于RNA，温度的影响尤为强烈，低温下细胞RNA水平较高，这表明为维持蛋白质合成和生长，核糖体进行了补偿性分配。这些实验表明，虽然磷限制是生长速率和细胞化学计量比的主要决定因素，但温度通过与磷的相互作用也有显著影响。在生态系统层面，营养物质和温度会相互作用，但温度可能会通过对分层状态和垂直营养通量的影响，对这些浮游植物特征产生更强的间接影响。
