Abstract
Summary Fifteen-year-old Norway spruces ( Picea abies [L.] Karst.) were grown in open top chambers (OTC) at ambient (A) and elevated (i.e. ambient + 350 μmol(CO 2 ) mol −1 ) concentrations of CO 2 (E) for four growing seasons (1992–1995). During this time period several examples of the depression of photosynthetic activities were observed for E needles. In order to better characterize the nature of this depression the gas exchange and fluorescence parameters were analyzed on current year needles during the last season (July 1995). The photon flux density response curves of CO 2 uptake (P N ) revealed a significandy reduced stimulation of P N for E needles as compared with short-term exposure to doubled CO 2 . Moreover, the sudden exposure of E shoots to 350μmol(CO 2 ) mol −1 at saturating irradiance revealed a depression of both P Nmax (by 20%) and quantum yield of PS II (by 32%) compared with A shoots measured at 350μmol(CO 2 ) mol −1 . The data supporting the diminished light harvesting system of photosystem II (PS II) in E shoots compared with A shoots were obtained from pigment analysis, low temperature fluorescence spectra and Chl a fluorescence induction kinetics. The relative proportion of inactive reaction centres of PS II determined from F pl of the fluorescence induction was 20% higher for E needles. These changes found for E needles mimicked an adaptation of PS II to increased irradiance compared with A needles. As the irradiance exposure was the same for the examined needles from both E and A spruces we suggest that these changes reported for E needles resulted from the feed-back limitation of photochemical reactions due to suppressed electron transport through the plastoquinone pool.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call