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Báo cáo lâm nghiệp: "Effect of nitrogen supply on growth and internal cycling within deciduous trees nitrogen"

Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp Original article đề tài:Effect of nitrogen supply on growth and internal cycling within deciduous trees nitrogen. | 666s Ann. Sci. For. 1989 46 suppl. 666s-668s Forest Tree Physiology E. Dreyer et al. eds. Elsevier INRA Effect of nitrogen supply on growth and internal nitrogen cycling within deciduous trees p. Millard Division of Plant Research Macaulay Land Use Research Institute Aberdeen AB9 2QJ Scotland Introduction Deciduous trees cycle nitrogen N internally by remobilising N from senescing leaves into woody tissues from where it is available for growth of new tissues the following year. Such cycling of N is important as a means of augmenting uptake of soil N since bud break in the spring can occur when conditions for uptake by the roots are suboptimal and before photosynthesis can provide carbon skeletons for amino acid synthesis. Remobilisation of stored N can therefore be a most important contribution to leaf growth at the start of the growing season Millard and Neilsen 1988 . Isotopic N has been used in several studies to trace the movement of previously assimilated N to the current year s growth e.g. Weimbaum and Muraoka 1986 . However few studies have assessed the magnitude of the storage pools of N in relation to current demands for growth. This paper reports the influence fertiliser N has upon internal N cycling using N supplied to apple trees grown in sand culture to quantify the proportion of N used for seasonal growth that was taken up by roots and that from internal cycling. Materials and Methods One year old apple trees Malus domestica Borkh were planted in sand in April 1987 and watered with nutrient solution throughout the experiments as described by Millard and Neilsen 1988 . In the first experiment N was supplied as 15NH415NO3 4.98 atom 15N in solutions containing either none 0.8 mol N-m-3 or 8.0 mol N-m-3. Plants were harvested through out the seasonal growth cycle In the second experiment plants were grown throughout 1987 with unlabelled N supplied at 8.0 mol N-m-3 until 1 September. Thereafter 3 treatments were applied withholding all further N .