Low recovery rates of fertiliser N in tree biomass are frequently reported due to the inefficiency of N fertilisers in afforested ecosystems. At Culloden (North East Scotland), only 13&'37 of 15N-urea fertiliser applied to Sitka spruce could be recovered in the above-ground tree biomass two years after fertilisation. Fertiliser N not taken up by trees was largely 'locked-up' in stable organic forms of N within the LFH layers of the soil profile. 15N-labelled litter was used in both field and microcosm experiments, the release and fate of litter-derived-N (LDN) being traced over the course of two growing seasons. In both experiments, the microbial biomass acted as a major sink for LDN. Measurement of soil microbial biomass was calibrated for Culloden soil samples by determination of a kEN-factor. Tree uptake of LDN, in the field, occurred within one month of labelled-litter application, with the foliage being the largest sink for LDN. Approximately 30&'37 of the N within the labelled-litter layer was taken up by the trees over the course of two growing seasons and was equivalent to 5.4 kg LDN ha-1 y-1. There was considerable mixing of the LFH and peat layers in Sitka spruce microcosm soil profiles. This was probably due to elevated soil animal population densities. After 18 months, approximately 83&'37 of LDN had been redistributed to other N pools in the microcosm. Uptake of LDN by seedlings accounted for 15.7&'37 of LDN after 12 months, the largest sink being the foliage, equivalent to 6.16 kg LDN ha-1 y-1. Again, the microbial biomass was a major sink for LDN. Measurement of availability (NH4+) N in Culloden soil samples incubated at different matric potentials and temperatures, appeared not to reflect N mineralisation rates. There was a strong interaction between temperature and soil matric potential, seedling uptake of N being greatest at 15oC and -16.0 kPa. The rate of turnover of the microbial biomass pool was identified as the key determinant of the rate of processing of LDN in forest soils.

Low fertiliser recoveries are often found for temperate coniferous forests and appear to be associated with the 'locking-up' of residual fertiliser N in stable organic forms. This phenomenon may well be caused by strong microbial immobilisation, out competing uptake by tree roots. This thesis investigates root/microbe competition for fertiliser-derived N (FDN) in microcosms of coniferous forest soil (supporting Sitka spruce seedlings) as well as in re-seeded blanket peat (supporting a mixed grass pasture). Combinations of selective microbial inhibitors, both with and without either 15N-labelled urea or NH4NO3, were applied to microcosms to selectively inhibit target microbial groups which may be competing with roots for FDN and determine the role of microbial immobilisation as a mechanism controlling N flow to seedlings/herbage. The dynamics of FDN novement into microcosm N pools was also studied in microcosms to which 15N-labelled urea was applied alone. At harvest, plant and soil N pools were analysed for 15N and total N (15 N &'43 14N). The impact of biocide and fertiliser N treatments on concentrations of target and non-target soil organisms were also determined. Biocidal (benlate and to a lesser extent streptomycin) inhibition of soil micro-organisms (particularly fungi) increased the uptake of both urea-derived N and NH4O3 N by Sitka spruce seedlings. Increases were associated with reduced percentages of FDA active hyphae and concentrations of FDN immobilised in the microbial biomass of LFH layer and peaty mineral soil. The results suggest that roots were competing with soil microbes for both fertiliser N forms. In conclusion this study has demonstrated the role of microbial biomass, particularly the dominant fungal component as a major competitive sink for fertiliser N and a major factor contributing to the low efficiency of fertiliser N in temperate coniferous forests. The study also has identified selective biocidal manipulation as a powerful technique for characterising competition between roots and microbes for nutrients in soil.

Poplar Bark Storage Proteins (BSP) are important in storing nitrogen (N) recovered from autumn-senescent leaves, and supply N for spring growth. Plants of Populus tremula x P. alba were transformed with a poplar BSP antisense cDNA fused to a double 35S promoter. Regenerated lines were screened for reduced BSP accumulation in short day photoperiod, and two lines were selected for further studies. Under long-day conditions, both BSP-antisense lines were characterized by larger leaves, longer internodes and slower growth rates, for a net shift in dry-matter partitioning from stem to leaf. Antisense lines also show reduced N concentration in leaf and stem tissue, and altered nitrate uptake. Grafting studies show that these effects on leaf and stem partitioning and N content are determined by the shoot genotype. These results indicate an important role of BSP in long day growth and partitioning. BSP-antisense plants did not show altered Nitrate Reductase activity, as determined by in vivo assay. Wild-type poplar plants were grown hydroponically on solutions of 0 to 30 mM nitrate, and NR activity determined on leaf, stem and root tissue. Leaf activity was >20x higher than root or stem, with the highest activity found in young expanding leaves. NR activity of both leaves and roots increased with N supply. During autumn, BSP-antisense leaves abscised earlier than the untransformed wt. Abscised wt leaves contained a higher proportion of pre-senescent N levels. Comparisons among ecotypes of P. deltoides and among clones of P. trichocarpa x P. deltoides demonstrated genetic variation in both time of BSP induction, and amount of BSP accumulation. In six P. deltoides ecotypes grown at a common site, time of maximum BSP mRNA was inversely correlated with latitude of origin. Eight to ten clones from each of six full-sib families of P. trichocarpa x P. deltoides were screened for SD BSP accumulation. Clonal differences in BSP accumulation were significant in 5 of 6 families, and clones with high BSP levels also had higher total stem N content. These results further confirm the importance of BSP in autumn N resorption. / Graduation date: 2000

Thesis (Ph. D.)--Oregon State University, 1981. / Typescript (photocopy). Includes bibliographical references (leaves 167-178). Also available on the World Wide Web.

Anaerobic ammonium oxidation (anammox) is a pathway that has been known for almost 2 decades, but few studies have investigated its importance in natural groundwaters. This thesis investigated the presence of anammox cells and the groundwater geochemistry of 2 sites (Elmira and Putnam) in southwestern Ontario where groundwaters are contaminated with high levels of nitrate and ammonium. Fluorescence in situ hybridization (FISH) was used to quantify the relative abundance of anammox cells in these waters. Our results showed that anammox cells could be detected in many wells at both sites and that their relative abundance varied between 0.45 and 4.81 % at the Putnam site, whereas it ranged between 0.8 to 8.4 % at the Elmira site. These values are within the same range as those obtained for marine and freshwater environments where anammox cells have been detected. In addition, indirect observations point to the fact that N cycling at the 2 sites might be linked to Fe and Mn reduction, but additional experiments are needed. In summary, our results corroborate the findings of N-labeled microcosm experiments which demonstrated that anammox was an important pathway of N cycling in those groundwaters and molecular analyses that detected important anammox organisms at the same sites.

No description available.

Anaerobic ammonium oxidation (anammox) is a pathway that has been known for almost 2 decades, but few studies have investigated its importance in natural groundwaters. This thesis investigated the presence of anammox cells and the groundwater geochemistry of 2 sites (Elmira and Putnam) in southwestern Ontario where groundwaters are contaminated with high levels of nitrate and ammonium. Fluorescence in situ hybridization (FISH) was used to quantify the relative abundance of anammox cells in these waters. Our results showed that anammox cells could be detected in many wells at both sites and that their relative abundance varied between 0.45 and 4.81 % at the Putnam site, whereas it ranged between 0.8 to 8.4 % at the Elmira site. These values are within the same range as those obtained for marine and freshwater environments where anammox cells have been detected. In addition, indirect observations point to the fact that N cycling at the 2 sites might be linked to Fe and Mn reduction, but additional experiments are needed. In summary, our results corroborate the findings of N-labeled microcosm experiments which demonstrated that anammox was an important pathway of N cycling in those groundwaters and molecular analyses that detected important anammox organisms at the same sites.

The provision of high quality analytical data is an essential prerequisite for understanding the biogeochemical cycling of nutrients in the aquatic environment. Due to the instability of samples collected for nutrient determinations however, in situ analysis is preferred. This approach also allows for high temporal and spatial resolution of the data and alteration of the sampling frequency to meet local environmental needs. Chapter One describes the role of nitrogen species, particularly ammonia and nitrate, in the aquatic environment, their sources, and possible environmental effects and summarises analytical techniques for their determination. Solid state miniaturised detectors and their suitability for in situ monitoring are also discussed. The characterisation and evaluation of a miniature Ocean Optics PSD - 1000 spectrometer and its suitability for field deployment is described in Chapter Two. Parameters investigated were optical resolution, wavelength repeatability, photometric linearity and instrumental noise and drift. The incorporation of the Ocean Optics PSD - 1000 miniature spectrometer into a gas diffusion Flow Injection (Fl) manifold for the determination of ammonia in natural waters is detailed in Chapter Three. Optimisation of the Fl parameters and analytical performance are discussed in detail. The development of an immobilised pH indicator and adaptation to a laminar Fl manifold is also considered. Chapter Four describes the use of the miniature spectrometer in a Fl manifold for the determination of nitrate and nitrite, with analytical figures of merit detailed. The increased information potential of the spectrometer (i.e. full spectral acquisition) facilitated the removal of the refractive index problem using dual wavelength correction. Miniaturisation and automation of the optimised nitrate manifold using micro-solenoid pumps and LabView™ graphical programming is described in Chapter Five. Field deployment of the automated system was assessed during a six week British Schools Exploring Society Expedition to Lesotho, S. Africa (in which an intensive biogeochemical survey of the Sehlabathebe National Park was conducted) and a three day campaign on the River Frome, Dorset, U.K. Chapter Six details the ion chromatographic analysis of major anions and cations (including ammonium and nitrate) in precipitation samples. Two sampling campaigns were conducted. One was at an urban site (Plymouth City Centre) from 27/01/98 - 11/05/98, and the influence of aerosol source on the chemical composition of Plymouth precipitation is discussed. The other involved the Austrian precipitation network and wet deposition trends for nitrate, ammonium and sulphate are discussed. The multivariate analysis technique of PCA was applied to both environmental datasets and the interpretation and merits of this statistical approach are considered.

Thesis (M.S. - Hydrology and Water Resources)--University of Arizona, 1989. / Includes bibliographical references (leaves 169-174).

Thesis (M.S.)--Oregon State University, 1997. / Typescript (photocopy). Includes bibliographical references. Also available on the World Wide Web.