Nutrient cycling and wood chemistry of sinuous Douglas-fir stands across different genetic gain levels in western Washington

Thesis (Master's)--University of Washington, 2018Stem sinuosity is a deformation which occurs in Douglas-fir and other tree species, which can be thought of as the displacement of the stem from its original direction over the total length of displacement. Nutritional deficiencies, such as those of copper, zinc, boron and calcium have been positively associated with increased stem form deformities. The objective of this study was to analyse available soil and total foliar concentrations of sinuous Douglas-fir stands, which were planted as a part of a genetic gains trial, which would give information about trends in nutrient cycling across sites and different levels of genetic gain. Increment wood cores, taken at breast height, were also analysed through FT-IR spectrophotometry and compared against sinuosity scores of the trees in order to get a more rigorous measurement of sinuosity. As the data collected was multivariate, Mantel test and PERMANOVA were used to study effects of site, genetic gain levels and pH on soil and foliar nutrients, with PCA and NMDS ordinations being used to visualize those trends. Relationships among genetic gain levels across different sites were also assessed to evaluate whether trees from a provenance suited to higher growth were better at mobilizing and sequestering nutrients in soils or needles. The stands were found to be deficient in boron and calcium, and moderately deficient with respect to zinc and nitrogen concentrations in the foliage. Trees from higher genetic gain level were able to accumulate nutrients more in their foliage, and there also seemed to be some differences with respect to available soil nutrients in the soils around them. Sinuosity was found to be negatively correlated with available soil boron, nitrogen, calcium, nitrate and foliar nitrogen while it was positively correlated to foliar sulphur, calcium, copper, zinc and available soil ammonium. Results of multivariate analyses show that site was the most important predictor which explained variation among soil nutrient concentrations. Genetic gain level explained some differences in soil/foliar nutrient concentrations, although not significantly so. Trends in that dataset and supporting data indicate the potential of proper genetic selection to reduce sinuosity while increasing growth. Absorbances obtained from wood cores taken at breast height were not found to be significant predictors of stem-form sinuosity and did not hint towards high lignin to cellulose ratios in the wood, although the principle components analysis did pinpoint a wavenumber range associated with glucosidic bonds as explaining the variation in the spectral dataset. This is encouraging and its potential for exploring differences in wood chemistry from sinuous sections of the stem would be worth investigating. The results of this study support the contention that no one single factor can explain stem-sinuosity. It is likely that sinuous growth in trees is caused by a combination of unbalanced nutrient concentrations and metal deficiencies, as were seen in this study, in addition to genetic, environmental and physiological factor