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 μmol mol−1 and elevated: 720 μmol mol−1). Budbreak was accelerated by elevated [CO2] accompanied with earlier temporal declines in the quantum yield of PSII electron transport (ΦPSII) and photochemical quenching (qL). Plants grown under elevated [CO2] showed pre-budbreak leaf starch content twice as high with no significant difference in ΦPSII from ambient-CO2-grown plants when compared at the same measurement [CO2], i.e., 360 or 720 μmol 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 − qP) Fv′/Fm′) was observed in plants grown under elevated [CO2] around budbreak when compared at their growth [CO2] (i.e., comparing (1 − qP) Fv′/Fm′ measured at 720 μmol mol−1 in elevated-CO2-grown plants with that at 360 μmol 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 Fv/Fm, 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.