Rapid Light-Response Curve of Chlorophyll Fluorescence in Terrestrial Plants: Relationship to CO(2) Exchange among Five Woody and Four Fern Species Adapted to Different Light and Water Regimes

The rapid light response of electron transport rate (ETR(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 ETR(R) and the steady-state light response of CO(2) exchange rate (A(S)) of terrestrial plants has not been studied in detail. In this study, we compared the ETR(R) and A(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 (g(s)) not being a main limiting factor for photosynthesis, ETR(R) and A(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 Alnus formosana was treated with low soil water and air humidity, because of the decrease in A(S) mainly due to stomatal closure, the ETR(R)–A(S) relation was not so close. In addition, at both 100 and 2000 μmol m(−2) s(−1) photosynthetic photon flux density (PPFD), ETR(R) and A(S) were significantly correlated within a plant group (i.e., woody plants and ferns) regardless of the broad difference in A(S) due to different species or environmental factors. The results indicate that the relationship between the ETR(R) and A(S) is varied by species. We concluded that 1) ETR(R) could reflect the variation in A(S) at each irradiance level within a species under well-watered conditions and 2) ETR(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.