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

The rapid light response of electron transport rate (ETRR), 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 ETRR and the steady-state light response of CO2 exchange rate (A(S)) of terrestrial plants has not been studied in detail. In this study, we compared the ETRR 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 degrees C) and with stomatal conductance (g(s)) not being a main limiting factor for photosynthesis, ETRR 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 ETRR-A(S) relation was not so close. In addition, at both 100 and 2000 mu mol m(-2) s(-1) photosynthetic photon flux density (PPFD), ETRR 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 ETRR and A(S) is varied by species. We concluded that 1) ETRR could reflect the variation in A(S) at each irradiance level within a species under well-watered conditions and 2) ETRR at 100 mu mol m(-2) s(-1) PPFD (as the efficiency of light capture) or 2000 mu mol 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.

Automated summary

The study compared the rapid light response of electron transport rate (ETRR) and the steady-state light response of CO2 exchange rate (A(S)) in different woody and fern species. The results showed a close relationship between ETRR and A(S) under well-watered conditions, but the relationship became less close under low soil water and air humidity conditions.