Rapid Light-Response Curve of Chlorophyll Fluorescence in Terrestrial Plants: Relationship to CO₂ Exchange among Five Woody and Four Fern Species Adapted to Different Light and Water Regimes

• Main Authors: Meng-Yuan Huang, Shau-Lian Wong, Jen-Hsien Weng
• Format: Article
• Language: English
• Published: MDPI AG 2021-02-01
• Series: Plants
• Subjects: electron transport rate; fern; photosynthetic rate; rapid light curve; stomatal conductance; tree
• Online Access: https://www.mdpi.com/2223-7747/10/3/445
• ISSN: 2223-7747

The rapid light response of electron transport rate (<i>ETR</i>_R), obtained from chlorophyll fluorescence parameters by short illumination periods (10–30 s) at each light level, can provide a rapid and easy measurement of photosynthetic light response in plants. However, the relationship between <i>ETR</i>_R and the steady-state light response of CO₂ exchange rate (<i>A</i>_S) of terrestrial plants has not been studied in detail. In this study, we compared the <i>ETR</i>_R and <i>A</i>_S for five woody and four fern species with different light and/or water adaptations. Under well-watered conditions, a constant temperature (25 °C) and with stomatal conductance (<i>g</i>_s) not being a main limiting factor for photosynthesis, <i>ETR</i>_R and <i>A</i>_S were closely related, even when merging data for regression analysis for a species grown under different light conditions and measured under different light intensity and air humidity. However, when <i>Alnus formosana</i> was treated with low soil water and air humidity, because of the decrease in <i>A</i>_S mainly due to stomatal closure, the <i>ETR</i>_R–<i>A</i>_S relation was not so close. In addition, at both 100 and 2000 μmol m⁻² s⁻¹ photosynthetic photon flux density (PPFD), <i>ETR</i>_R and <i>A</i>_S were significantly correlated within a plant group (i.e., woody plants and ferns) regardless of the broad difference in <i>A_S</i> due to different species or environmental factors. The results indicate that the relationship between the <i>ETR</i>_R and <i>A</i>_S is varied by species. We concluded that 1) ETR_R could reflect the variation in <i>A</i>_S at each irradiance level within a species under well-watered conditions and 2) <i>ETR</i>_R at 100 μmol m⁻² s⁻¹ PPFD (as the efficiency of light capture) or 2000 μmol m⁻² s⁻¹ PPFD (as a maximum photosynthetic parameter) could be used to compare the photosynthetic capacity within a plant group, such as woody plants and ferns.