Phytoplankton primary productivity: A dual-incubation approach for direct comparison of photosystem II photosynthetic flux (JVPII) and 14C-fixation experiments

IF 2.1 3区 地球科学 Q2 LIMNOLOGY
Nina Schuback, Kevin Oxborough, Mary Burkitt-Gray, Patricia López-García, Matthew D. Patey, Emily Hammermeister, Alan Wright, C. Mark Moore
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Abstract

Singe-turnover active chlorophyll a fluorometry (STAF) can be used to assess phytoplankton photosynthetic rates in terms of the photosystem II photochemical flux (JVPII, μmol e m−3 s−1) instantaneously, autonomously, and at high resolution. While JVPII provides an upper limit to rates of phytoplankton primary productivity in units of carbon fixation, the conversion between these two rates is variable, limiting our ability to utilize high-resolution JVPII data to monitor phytoplankton primary productivity. Simultaneous measurements of JVPII and 14C-fixation help in understanding the factors controlling the variable ratio between the two rates. However, to date, methodological inconsistencies, including differences in incubation lengths and light quality, have greatly inhibited practical assessment of such electron to carbon ratios (Φe,C, mol e mol C−1). We here present data from a range of dual-incubation experiments in northeast Atlantic waters during which JVPII and 14C-fixation were measured simultaneously on the same sample. Time-course experiments show how Φe,C increases with incubation length, likely reflecting the transition from gross to net 14C-fixation. Dual-incubation experiments conducted under different light levels show a tendency for increased Φe,C under (super-)saturating light. Finally, data from a diurnal experiment demonstrate how Φe,C increases over the course of a day, due to downregulation of 14C-fixation. We provide a detailed description of our methodological approach, including a critical discussion of improvements to the calculation of JVPII implemented in the LabSTAF instrument used for active fluorescence measurements and the limitations of the well-established 14C-fixation approach.

Abstract Image

浮游植物初级生产力:直接比较光系统 II 光合通量(JVPII)和 14C 固定实验的双培养箱方法
单翻转活性叶绿素 a 荧光测定法(STAF)可用于即时、自主和高分辨率地评估浮游植物光合速率,即光合系统 II 光化学通量(JVPII,μmol e- m-3 s-1)。虽然 JVPII 提供了以碳固定为单位的浮游植物初级生产力速率的上限,但这两个速率之间的转换是可变的,这限制了我们利用高分辨率 JVPII 数据监测浮游植物初级生产力的能力。同时测量 JVPII 和 14C 固定率有助于了解控制这两种速率之间可变比率的因素。然而,迄今为止,方法上的不一致(包括培养时间和光照质量的差异)极大地阻碍了对电子与碳比率(Φe,C, mol e- mol C-1)的实际评估。我们在此介绍在大西洋东北部水域进行的一系列双培养实验的数据,在这些实验中,对同一样本同时测量了 JVPII 和 14C 固定。时间历程实验表明,Φe,C 随培养时间的延长而增加,这可能反映了 14C 总固定向净固定的转变。在不同光照水平下进行的双培养实验表明,在(超)饱和光照下,Φe,C 有增加的趋势。最后,来自昼夜实验的数据表明,由于 14C 固定的下调,Φe,C 在一天中会增加。我们详细描述了我们的研究方法,包括对用于主动荧光测量的 LabSTAF 仪器在计算 JVPII 方面的改进以及成熟的 14C 固定方法的局限性的批判性讨论。
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来源期刊
CiteScore
4.80
自引率
3.70%
发文量
56
审稿时长
3 months
期刊介绍: Limnology and Oceanography: Methods (ISSN 1541-5856) is a companion to ASLO''s top-rated journal Limnology and Oceanography, and articles are held to the same high standards. In order to provide the most rapid publication consistent with high standards, Limnology and Oceanography: Methods appears in electronic format only, and the entire submission and review system is online. Articles are posted as soon as they are accepted and formatted for publication. Limnology and Oceanography: Methods will consider manuscripts whose primary focus is methodological, and that deal with problems in the aquatic sciences. Manuscripts may present new measurement equipment, techniques for analyzing observations or samples, methods for understanding and interpreting information, analyses of metadata to examine the effectiveness of approaches, invited and contributed reviews and syntheses, and techniques for communicating and teaching in the aquatic sciences.
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