Spectral overlap of far-red light with chlorophyll fluorescence causes artifacts in PAM-based Φ PSII determination.

Abstract

Far-red light (FR, 700-800 nm) can enhance photosynthesis by stimulating photosystem I (PSI). However, during chlorophyll fluorescence (CF) measurements using pulse-amplitude modulation (PAM) fluorometry, unusually high quantum yields of photosystem II ( Φ PSII ) have been observed under high FR light intensities, raising concerns about measurement artifacts. To test this, we constructed light response curves for sweet basil ( Ocimum basilicum L.) grown under light-emitting diode (LED) light (R:G:B = 44%:18%:38%) with varying photosynthetic photon flux densities (PPFD, 0-1,000 μmol m -2 s -1 ) and FR fractions (0, 0.26, 0.45, and 0.63). FR treatments consistently increased Φ PSII , but when total photon flux density (TPFD, 400-800 nm) exceeded 1,000 μmol m -2 s -1 , Φ PSII rose abruptly. Nonfluorescent reference tests using white and black paper confirmed that FR induced spurious fluorescence signals, likely due to spectral overlap between FR photons and the PAM detection range (680-760 nm). Tilting the LED panel to reduce reflected FR eliminated the abrupt Φ PSII peak but introduced unexpectedly increased Φ PSII across treatments, likely due to probe-induced shading. These findings demonstrate that high-intensity FR can confound PAM-based CF measurements by producing spurious signals unrelated to plant physiology. Accurate and reliable assessment of photosynthetic performance under extended spectral lighting conditions requires careful management of lighting geometry and FR intensity.

Plant phenotyping relevance

PAMによる光合成量子収率測定のアーティファクトを検証し、照明条件と測定 geometry が植物生理形質の取得精度に与える影響を評価しているため、測定法の技術的検証が中心である。

Code and data availability

The paper reports PAM fluorometry measurements of ΦPSII in sweet basil under far-red LED treatments, but no public phenotype dataset, images, code, or trained models are deposited. The data availability statement only points to the article/supplementary material and directs further inquiries to the corresponding author

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