Photosynthetic and fatty acid acclimation of four phytoplankton species in response to light intensity and phosphorus availability

Photosynthetic acclimation of phytoplankton to lower irradiation can be met by several strategies such as increasing the affinity for light or increasing antenna size and stacking of the thylakoids. The latter is reflected by a higher proportion of polyunsaturated fatty acids (PUFAs). Additionally, photosynthetic capacity (P_max), respiratory losses, and proton leakage can be reduced under low light. Here we consider the effect of light intensity and phosphorus availability simultaneously on the photosynthetic acclimation and fatty acid composition of four phytoplankters. We studied representatives of the Chlorophyceae, Cryptophyceae and Mediophyceae, all of which are important components of plankton communities in temperate lakes. In our analysis, excluding fatty acid composition, we found different acclimation strategies in the chlorophytes <i>Scenedesmus quadricauda, Chlamydomonas globosa</i>, cryptophyte <i>Cryptomonas ovata</i> and ochrophyte <i>Cyclotella meneghiniana</i>. We observed interactive effects of light and phosphorus conditions on photosynthetic capacity in <i>S. quadricauda</i> and <i>Cry. ovata. Cry. ovata</i> can be characterized as a low light-acclimated species, whereas <i>S. quadricauda</i> and <i>Cyc. meneghiniana</i> can cope best with a combination of high light intensities and low phosphorus supply. Principal component analyses (PCA), including fatty acid composition, showed further species-specific patterns in their regulation of P_max with PUFAs and light. In <i>S. quadricauda</i> and <i>Cyc. meneghiniana</i>, PUFAs negatively affected the relationship between P_max and light. In <i>Chl. globosa</i>, lower light coincided with higher PUFAs and lower P_max, but PCA also indicated that PUFAs had no direct influence on P_max. PUFAs and P_max were unaffected by light in <i>Cry. ovata</i>. We did not observe a general trend in the four species tested and concluded that, in particular, the interactive effects highlight the importance of taking into account more than one environmental factor when assessing photosynthetic acclimation to lower irradiation.

浮游植物（phytoplankton）对低光照的光合适应可借助多种策略达成，例如提升对光的亲和力、增大捕光天线尺寸以及堆叠类囊体（thylakoids）。其中，后者可通过更高比例的多不饱和脂肪酸（polyunsaturated fatty acids, PUFAs）得以体现。此外，低光环境下光合能力（P_max）、呼吸损耗与质子泄漏均可得到有效降低。本研究同时探讨光照强度与磷有效性对四种浮游植物的光合适应及脂肪酸组成的影响。我们选取了绿藻纲（Chlorophyceae）、隐藻纲（Cryptophyceae）与中藻纲（Mediophyceae）的代表物种，上述类群均为温带湖泊浮游生物群落的重要组成部分。在排除脂肪酸组成的分析框架下，我们发现绿藻物种四尾栅藻（*Scenedesmus quadricauda*）、球状衣藻（*Chlamydomonas globosa*），隐藻卵形隐藻（*Cryptomonas ovata*）以及褐藻门氏圆筛藻（*Cyclotella meneghiniana*）存在各异的适应策略。我们观察到，光照与磷条件的交互作用对四尾栅藻（*S. quadricauda*）和卵形隐藻（*Cry. ovata*）的光合能力存在显著影响。卵形隐藻可被归为低光适应型物种，而四尾栅藻与门氏圆筛藻（*Cyc. meneghiniana*）则最能适配高光照强度与低磷供给的组合环境。包含脂肪酸组成的主成分分析（Principal Component Analysis, PCA）显示，各物种在通过PUFAs调控P_max与光照的关联时，存在进一步的种特异性模式。在四尾栅藻与门氏圆筛藻中，PUFAs对P_max与光照之间的关系产生负向调控作用。在球状衣藻中，更低的光照条件与更高的PUFAs含量及更低的P_max相匹配，但PCA结果同时表明，PUFAs并未对P_max产生直接影响。卵形隐藻的PUFAs与P_max均不受光照的调控。我们未在受试的四个物种中观察到统一的规律，并据此得出结论：尤其是交互作用效应凸显了在评估浮游植物对低光照的光合适应时，需纳入多种环境因子的重要性。