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Effect of dead phytoplankton cells on the apparent efficiency of photosystem II

机译：死亡的浮游植物细胞对光系统II表观效率的影响

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Measurements of the efficiency of photosystem (PS) II have become widespread in biological oceanography, and various forms are used to assess the 'health' of marine phytoplankton and to help estimate primary productivity. Absolute values of PS II efficiency depend to some extent on the measuring system, but changes in PS II efficiency are most commonly interpreted in terms of cellular acclimations to changing irradiance (including photoacclimation and photoinhibition) and nutrient availability (especially N and Fe). Recent measurements of phytoplankton viability in the surface ocean have revealed that in many regions phytoplankton assemblages may contain large proportions of dead cells. The effect of these dead cells on apparent PS II efficiency is largely unknown. By mixing live and dead cells and measuring PS II efficiency, we show that the presence of photosyntheti-cally non-functional (dead) cells has surprisingly little effect; in a number of species, mixtures in which 50% of the cells were dead had rnvalues of 0.5, similar to values often found in natural assemblages. A simple model indicates that the non-linear nature of the fluorescence ratio is responsible for this unexpected result. We conclude that relatively high values of PS II efficiency cannot be used as evidence of low mortality. Our findings highlight the need for more information on the physiological status of both eukaryotic and prokaryotic microalgae in nature.
机译：在生物海洋学中，对光系统（PS）II效率的测量已变得很普遍，并且使用各种形式来评估海洋浮游植物的“健康”并帮助估算初级生产力。 PS II效率的绝对值在某种程度上取决于测量系统，但是PS II效率的变化最常见的解释是细胞适应辐照度（包括光适应和光抑制）和养分利用率（尤其是N和Fe）的变化。最近对海洋表层浮游植物生存力的测量表明，在许多地区，浮游植物组合可能包含大量死细胞。这些死细胞对表观PS II效率的影响在很大程度上尚不清楚。通过混合活细胞和死细胞并测量PS II效率，我们发现光合非功能性（死）细胞的存在令人惊讶地几乎没有影响；在许多物种中，有50％的细胞死亡的混合物的nr值为0.5，这与自然组合中常见的值相似。一个简单的模型表明，荧光比的非线性性质是造成这种意外结果的原因。我们得出的结论是，相对较高的PS II效率值不能用作低死亡率的证据。我们的发现突出表明需要更多有关自然界中真核和原核微藻的生理状况的信息。

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