ABSTRACT

Integration of pulse amplitude modulated (PAM) fluorometry and conventional methods for estimating carbon assimilation in microalgae is important for physiological, ecological and economic purposes. In this study, we compared PAM fluorometry and carbon-14 (¹⁴C) uptake techniques to estimate the carbon fixation rate in Chlorella vulgaris under controlled laboratory conditions. The key parameter for this comparison was the electron yield for carbon fixation (Ф_e), commonly assumed when converting electron transport rate (ETR) values into the chlorophyll-specific carbon fixation rate (P^B). Additional analyses of maximum (Φ_M) and effective (Φ’_M) quantum efficiency of photosystem II, photochemical (qP) and non-photochemical (NPQ) quenching, and photosynthesis-irradiance response curves demonstrated that the photophysiology of C. vulgaris did not change after a 2-h incubation with NaH¹⁴CO₃ and Na₂CO₃ (control). The association of P^B obtained through the ¹⁴C method (151 ± 8.77 µmol C [mg chl a]^–1 h^–1) with ETR (411 ± 3.91 µmol e⁻ [mg chl a]^–1 h^–1) resulted in an average Ф_e of 0.37 ± 0.02 µmol C [µmol e⁻]^–1, which is higher than theoretical Ф_e values usually reported in the literature (e.g. 0.20 and 0.25). We attributed this discrepancy to a possible inaccuracy in ETR due to underestimated values of chlorophyll-specific absorption cross-section (a*) and the common assumption that only 50% of total light is absorbed by photosystem II. We here demonstrate the importance of associating chlorophyll fluorescence with other primary production techniques, so that adjustments to calculation procedures can be made in accordance to species-specific physiological traits and particularities regarding culturing conditions.

摘要

脉冲幅度调制 (PAM) 荧光测定法和用于估计微藻中碳同化的常规方法的集成对于生理、生态和经济目的很重要。在这项研究中，我们比较了 PAM 荧光法和碳 14 ( ¹⁴ C) 吸收技术，以估计受控实验室条件下小球藻的碳固定率。这种比较的关键参数是碳固定的电子产率 ( Ф _e )，通常在将电子传输速率 ( ETR ) 值转换为叶绿素特定碳固定速率 ( PB ) 时^假设。最大值 ( Φ _M ) 和有效 (Φ' _M ) 光系统 II 的量子效率、光化学 ( qP ) 和非光化学 ( NPQ ) 猝灭以及光合作用-辐照度响应曲线表明C. vulgaris的光生理学在与 NaH ¹⁴ CO孵育 2 小时后没有改变₃和 Na ₂ CO ₃ (对照)。通过¹⁴ C 方法获得的P ^B (151 ± 8.77 µmol C [mg chl a ] ^–1 h ^–1 ) 与ETR (411 ± 3.91 µmol e ^- [mg chl a ]^–1 h ^–1 ) 的平均Ф _e为 0.37 ± 0.02 µmol C [µmol e ^- ] ^–1，高于文献中通常报道的理论Ф _{e值（例如 0.20 和 0.25）。}我们将这种差异归因于ETR可能不准确，因为叶绿素特异性吸收截面的值被低估（a*) 以及只有 50% 的总光被光系统 II 吸收的普遍假设。我们在这里展示了将叶绿素荧光与其他初级生产技术相关联的重要性，以便可以根据物种特定的生理特征和培养条件的特殊性对计算程序进行调整。