Light‐Induced Adaptive Responses under Greenhouse and Controlled Conditions in the Fern Pteris cretica var. ouvrardii

The photosynthetic capabilities of the fern Pteris cretica var. ouvrardii were analysed by means of the light response curves of CO2 exchange. In control growth conditions (greenhouse, low‐light: 20–32 W m−2); photosynthesis was shown to be saturated for low irradiance (20–25 W m−2); the saturating photosynthetic rate, very low as compared to higher plants, was due to an extremely high intracellular resistance. When irradiance during the photosynthesis measurement was higher than 60–80 W m−2, a constant decline of net CO2 exchange as a function of time was observed. When irradiance during growth was enhanced, whether in greenhouse (20–250 W m−2) or controlled (62 W m−2) conditions, the first fronds that had developed in the new condition from the crosier stage exhibited decreased net maximal photosynthesis and a decreased efficiency in low light, but saturating irradiance was unmodified. However, the fronds whose entire differentiation (from meristem) occurred under these moderate irradiances (plants defoliated of all fronds and crosiers at the time of transfer), possessed more efficient photosynthetic characteristics than control plants. Pteris is able to grow under extreme shade conditions (4–8 W m−2); light saturating photosynthesis and efficiency are higher under extreme shade than under control conditions. These adaptive characteristics indicate that Pteris is a well‐adapted shade species.