Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp quốc tế, đề tài: "Limitation of photosynthetic activity by CO 2 availability in the chloroplasts of oak leaves from different species and during drought. | Ann Sci For 1996 53 243-254 Elsevier INRA 243 Original article Limitation of photosynthetic activity by co2 availability in the chloroplasts of oak leaves from different species and during drought o Roupsard p Gross E Dreyer Équipe bioclimatologie et écophỵsiologie unite d ecophysiologie forestiere Centre de Nancy Inra 54280 Champenoux France Received 2 November 1994 accepted 26 June 1995 Summary It has recently been suggested that the low photosynthesis rates in tree species as compared to highly productive crops is at least partly due to resistances opposing the co2 fluxes in the mesophyll of tree leaves. To validate this assertion values of co2 mole fractions in the chloroplasts of leaves from Quercus petraea Q robur Q ilex and Populus sp were estimated on the basis of the analysis of the partitioning of light driven electron flow between fractions used for the carboxylation or the oxygenation of RuBP by Rubisco. The procedure used included i a measure of total light driven electron flows derived from the chlorophyll a fluorescence ratio AFZFm which is proportional to the photochemical efficiency of PS II multiplied by incident irradiance and a calibration coefficient ii an estimation of the electron flux devoted to carboxylation obtained from net co2 assimilation and respiration rate measurement and using the known electron requirements four electrons for co2 or 02 fixation Hi the derivation of the co2 mole fraction in the chloroplasts from the specificity factor of Rubisco and the ratio of carboxylation oxygenation of RuBP. Results showed that in the absence of drought stress the mole fraction of co2 in the chloroplasts 35-45 of the atmospheric one was much lower than the calculated substomatal one 60-70 of the atmospheric in all species. Moreover lowest values were Correspondence and reprints dreyer@ Abbreviations A net co2 assimilation rate pmol m 2 s 1 A1 net co2 assimilation under nonpho-torespiratory 1 02 conditions Rd nonphotorespiratory .
