Photosynthetic traits around budbreak in pre-existing needles of Sakhalin spruce (Picea glehnii) seedlings grown under elevated CO₂ concentration assessed by chlorophyll fluorescence measurements.

摘要

To assess the effects of elevated CO₂ concentration ([CO₂]) on the photosynthetic properties around spring budbreak, we monitored the total leaf sugar and starch content, and chlorophyll fluorescence in 1-year-old needles of Sakhalin spruce (Picea glehnii Masters) seedlings in relation to the timing of budbreak, grown in a phytotron under natural daylight at two [CO₂] levels (ambient: 360 micro mol mol-1 and elevated: 720 micro mol mol-1). Budbreak was accelerated by elevated [CO₂] accompanied with earlier temporal declines in the quantum yield of PSII electron transport ( Phi _PSII) and photochemical quenching (q_L). Plants grown under elevated [CO₂] showed pre-budbreak leaf starch content twice as high with no significant difference in Phi _PSII from ambient-CO₂-grown plants when compared at the same measurement [CO₂], i.e., 360 or 720 micro mol mol-1, suggesting that the enhanced pre-budbreak leaf starch accumulation might not cause down-regulation of photosynthesis in pre-existing needles under elevated [CO₂]. Conversely, lower excitation pressure adjusted for the efficiency of PSII photochemistry ((1 - q_P) F_v'/F_m') was observed in plants grown under elevated [CO₂] around budbreak when compared at their growth [CO₂] (i.e., comparing (1 - q_P) F_v'/F_m' measured at 720 micro mol mol-1 in elevated-CO₂-grown plants with that at 360 micro mol mol-1 in ambient-CO₂-grown plants), which suggests lower rate of photoinactivation of PSII in the elevated-CO₂-grown plants around spring budbreak. The degree of photoinhibition, as indicated by the overnight-dark-adapted F_v/F_m, however, showed no difference between CO₂ treatments, thereby suggesting that photoprotection during the daytime or the repair of PSII at night was sufficient to alleviate differences in the rate of photoinactivation.