Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp Original article đề tài: Seasonal variations in photosynthetic activity of spruces as determined by chlorophyll fluorescence. | 483s Ann. Sci. For. 1989 46 suppl. 483s-489s Forest Tree Physiology E. Dreyer et al. eds. Elsevier INRA Seasonal variations in photosynthetic activity of spruces as determined by chlorophyll fluorescence . Lichtenthaler II. Rinderle and M. Haitz Botanisches Institut II Plant Physiology and Biochemistry University of Karlsruhe Kaiserstr. 12 D-7500 Karlsruhe . Introduction In photosynthetically active green plant tissue leaves needles the largest part of the light energy absorbed by the pigments chlorophylls carotenoids is used for photosynthesis photosynthetic quantum conversion . A minor part is re-emitted as chlorophyll fluorescence whose spectrum exhibits maxima near 690 and 735 nm Lichtenthaler et al. 1986 Lichtenthaler and Rinderle 1988a . The light-induced in vivo chlorophyll fluorescence of a predarkened green leaf or needle sample shows a transient which is known as fluorescence induction kinetics and variable fluorescence Kautsky effect . Upon illumination one observes a fast fluorescence rise ca 400 ms to a maximum fmax followed by a slow fluorescence decrease fd to the steady state fluorescence 4 . The fluorescence decrease ratio Rfd ffj fs Aid-values at 690 nm which indicates the potential photosynthetic activity of a leaf area has successfully been established as a very suitable vitality index and stress indicator in plants Lichtentha-ler and Rinderle 1988a b Lichtenthaler et al. 1986 Strasser et al. 1987 . The height of the Afd-values measured in the 690 and 730 nm regions reflects the potential photosynthetic activity of leaves as is demonstrated by parallel measurements of the net CO2-assimilation rate PN. The A d-values are an indicator of the intactness of the internal photosynthetic apparatus. Though they usually parallel the net CO2-assimilation rates they are a different parameter and independent of stomatai opening. With an additional apparatus the PAM fluorometer Schreiber et al. 1986 one can determine the photochemical Q- and the .