Photosynthetic acclimation of shade-grown red pine (Pinus resinosa Ait.) seedlings to a high light environment.

摘要

Photosynthetic light acclimatization in red pine (Pinus resinosa) seedlings was examined in a greenhouse study, in order to understand the physiological response of this species to increased light intensity following release from competition. Seedlings grown in a high (HL), medium (ML) or low (LL) light environment for 12 weeks were transferred to high light. Gas exchange and chlorophyll fluorescence of ML and LL seedlings were measured prior to and following transfer and compared with the HL control treatment. Photosynthetic characteristics were related to initial light treatment and time after transfer. Acclimatization of gas exchange features to high light in shade formed ML and LL foliage was relatively rapid, with similar values among light treatments within 57 days of transfer. Acclimatization of net photosynthetic rate was similar in ML and LL seedlings, and was associated primarily with increased mesophyll conductance to CO2. The ratio of variable to maximal chlorophyll fluorescence (Fv/Fm, a measure of the efficiency of photosystem II) decreased initially after transfer, especially in LL seedlings, but recovered to normal values after 57 days. The results indicate that red pine seedlings appear to be well adapted for photosynthetic acclimatization to high light intensity, consistent with that reported for other early successional tree species.