Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp Original article đề tài: Photosynthesis and leaf longevity in alder, birch and ash seedlings grown under different nitrogen. | 476s Ann. Sà. For. 1989 46 suppl. 476s-478s Forest Tree Physiology E. Dreyer etal. eds. Elsevier INRA Photosynthesis and leaf longevity in alder birch and ash seedlings grown under different nitrogen levels T. Koike1-2 and M. Sanada2 1 Swiss Federal Institute of Forestiy Research Birmensdorf ZH Switzerland and 2 Hokkaido Branch Forestry and Forest Products Research Institute Sapporo Japan Introduction With application of nitrogen fertilizers photosynthetic rates increase Field and Mooney 1986 and the leafy period is prolonged Linder and Rook 1984 . There is a negative correlation between the maximum photosynthetic rate and its duration Koike 1987 . However there is little information about the longevity of individual leaves after nitrogen treatments Linder and Rook 1984 . We report the relationship between photosynthetic rates and leaf longevity of deciduous broad-leaved tree seedlings in relation to the anatomical characteristics in leaves. Materials and Methods One yr old seedlings of alder Alnus hirsuta Turcz. birch Betula maximowicziana Regel and ash Fraxinus mandshurica Rupr. var. japonica Maxim. were planted in unglazed pots diameter 21 cm filled with surface soil of the ộursery including volcanic ash Sanada 1975 . As nitrogen fertilizers ammonium sulfate was supplied 4 times in each pot. Phosphate ammonium g was provided as basal dressing. Until the final supply total amount of nitrogen in each pot was and g. Supplying date and the percentage against the total amount was July 1 40 July 24 20 Aug. 20 20 and Sept. 15 20 respectively. Gas exchange rates were determined by an open system with an infrared gas analyzer URA2S Shimadzu in the summer of 1984. Air was stored in an airbag and was humified. The flow rate into the chamber 20 X 18 X cm3 was cm3 s-1. Measurement conditions were regulated strictly with an artificially illuminated chamber Koike 1987 . Leaf temperature was kept at the optimum temperature of 20 C and was monitored
