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Title: The uptake and dynamics of nitrogen in young stands of Sitka spruce
Author: Ibrahim, K. G.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1990
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The effects of nutrient and biomass distribution on growth and nutrition of an age series of young stands of Sitka spruce (Picea sitchensis (Bong.) Carr) prior to canopy closure have been studied to find out if the concept of steady-state nutrient status, pioneered by T. Ingestad, is valid under field conditions. Three similar experimental sites for this purpose were located at Manor Valley, Glentress and Innerleithen Forestry Commission Plantations, 40 to 50 km south of Edinburgh. Detailed quantitative analysis of the biomass and nutrient dynamics on tree growth have been made in relation to nitrogen uptake rate and nitrogen productivity. The results obtained showed that, leaves and branches constitute over 65% of the biomass production with over 75% of N, P and K nutrients. Significant allometric relationships were established between dry biomass, nutrient contents and tree dimensions for the difference component parts of the trees at the three ages (R2 = 0.66-0.99). Basal area provided a reliable estimation of leaf area up to canopy closure. Maximum leaf area density and leaf nitrogen mass density were determined with respect to leaf age and position of leaves within the tree crown. The distribution of leaf nitrogen on an area basis in older trees was consistent with an optimal distribution for photosynthetic activity with depth in the canopy. This may enhance whole plant carbon gain over that possible from a uniform distribution of fixed amounts of nitrogen among leaves of different age class in the canopy. A model was developed for specific leaf area distribution within the canopies and this indicated the potential of the photosynthetic apparatus to acclimate to low light conditions in dense stands compared to open stands. Particular attention has been given to biomass and nutrient productivity models to investigate ecophysiological processes and growth efficiency as a result of interactions between nutrition and stand structure, especially with respect to leaf age and the position of leaves within the tree crown. This showed that the comparatively stable canopy of older Sitka spruce trees seems to develop morphological and physiological gradients of leaf biomass and nitrogen distribution that parallel the gradient of decreasing light with increasing depth in the canopy. This thesis has demonstrated that the concept of relative addition rate, developed in the laboratory, was found to be consistent with exponential growth under field conditions and that a stable nitrogen status must have been achieved since the relative growth rate (R) and nitrogen uptake rate (RN) were found to agree very closely (R = 0.69 a-1, RN = 0.66 a-1). The efficiency of growth of young Sitka spruce was attributed to dynamic coupling between nitrogen content and growth rate, and it was concluded that higher productivity could be achieved by implementing fertilizer regimes that are designed to increase nitrogen uptake rate whilst maintaining a stable nitrogen status. The results in this thesis are relevant for estimating nutrient drain on forest sites and the prediction of the consequences of fertilizer application, and they also highlight important features of Sitka spruce for intensified management planning.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available