tailieunhanh - Báo cáo lâm nghiệp: "Comparative study species"

Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp Original article đề tài:Comparative study species. | 663s Ann. Sei. For. 1989 46 suppl. 663s-665s Forest Tree Physiology E. Dreyer et al. eds. Elsevier INRA Comparative study of nitrogen assimilation in woodland species J. Pearson . Clough and . Kershaw Department of Biology Darwin University College London Gower Street London WC1E6BT . Introduction Trees differ in their ability to assimilate nitrate in their leaves Smirnoff ef al. 1984 . In Australian rain forest trees a relatively high capacity for leaf nitrate assimilation is characteristic of pioneer species or species of open communities. Those of closed communities tend to have lower shoot root nitrate reductase NR ratios Stewart et al. 1988 . This study compares the level of leaf NR activity in several northern temperate tree species. The capacity for assimilation of foliar supplied nitrate is discussed. Results and Discussion Five tree species have been sampled throughout the 1988 season for leaf NR activity for method see Smirnoff et al. 1984 . The climax species beech had the lowest level of NR fwt while the pioneer species birch exhibited the highest activity . Of 3 conifers tested Scots pine was higher than either Sitka spruce or Norway spruce . In the case of Scots pine and birch a marked seasonal variation in leaf NR activity existed Fig. 1 . Pine had a relatively high leaf NR activity in the spring which could be associated with a flush of soil nitrification and rising sap. Birch however showed a relatively low level for NR in buds and expanded leaves until near the onset of autumn. At this time a 5-fold increase in activity had occurred. This phenomenon was noted in 1987 and at 2 other sites this year. Three possibilities seem likely 1 stored nitrate within the leaf vacuole is being released with the onset of senescence 2 the flux of nitrate from root to shoot is being increased 3 the onset of senescence could have led to the removal of some form of end product inhibitor. The exact reason is as yet .

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