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Studies of western hemlock nutrition White, Joseph Barry

Abstract

Western hemlock (Tsuga heterophylla) is an important commercial tree species in coastal British Columbia. A series of studies was carried out to further our understanding of western hemlock nutrition, which may ultimately provide for an operational fertilization program involving this species. Eight immature western hemlock stands were fertilized with additions of N , two levels of P (100 and 500 kg/ha) and a blend treatment. All stands responded to N additions to varying degrees but did not show evidence of a response to P or blend additions. Arginine concentrations increased following N only additions but decreased when P or the blend fertilizer was also applied. Concentrations of organic and inorganic P were determined. The organic fraction peaked at approximately 0.12% and further increases in total P were allocated to the inorganic fraction. ³²P uptake was measured in excised fine roots from eight stands that had been previously fertilized. Uptake varied significantly with treatment but was not related to growth response. Uptake rates were related to total P and inorganic P in current-year foliage. The latter suggested that tree perception of P deficiency is foliar based. A 5-year-old western hemlock plantation was fertilized to investigate the effect of improved nutrition on the photosynthetic apparatus. The additions of N and P, the latter at a rate of 300 kg/ha, improved height growth. The effects of nutrient additions were examined by analyses of photosynthetic rates, carbon isotope discrimination, chlorophyll concentrations, and chlorophyll fluorescence. Improved growth, and the concomitant changes in the various photosynthetic parameters, was mirrored by changes in chloroplast ultrastructure. An 18-year-old stand comprised of Douglas-fir and western hemlock was fertilized with N and two levels of P. The distribution of P among various P metabolites using perchloric acid extracts was attempted using NMR. An in vitro investigation was attempted to fractionate total P, at a cellular level, into vacuolar and cytoplasmic fractions. The physiological parameters measured in this thesis were more sensitive indicators of N and P status, but a longer growth response period is required before their value in predicting the long-term response of this species to fertilization can be concluded.

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