<p>The microbial life of sub-Antarctic islands plays a key role in the islands ecosystem, with microbial activities providing the majority of nutrients available for primary production. Knowledge of microbial diversity is still in its infancy and this is particularly true regarding the diversity of micro-organisms in the Antarctic and sub-Antarctic regions. One particularly important functional group of micro-organisms is the diazotrophs, or nitrogen-fixing bacteria and archaea. This group have not been well studied in the sub-Antarctic region, but play an important role in the nutrient cycling of the island. This thesis explored the diversity of nitrogen-fixing organisms in the soil of different ecological habitats on the sub-Antarctic Marion Island.</p>

The deposition of atmospheric nitrogen is now recognized as a major driver of biodiversity changes at mid to high latitudes. It has previously been shown that regional variations in wet nitrogen deposition in the British Isles are reflected in broad targeted chemical parameters in the common heathland lichen Cladonia portentosa. A more detail analysis of alterations in the metabolic pathways in Cladonia portentosa collected from different locations within the UK was undertaken by applying the environmental metabolomics approach. Fourier transform infrared spectroscopy (FTIR) and liquid chromatography mass spectrometry (LC-MS) were applied in combination with principal component analysis (PCA) and partial least squares regression analysis (PLSR). The latter statistical method was used to correlate measured variables with modelled atmospheric data including wet nitrogen deposition, nitrogen concentration and precipitation. While FTIR in combination with PCA and PLSR revealed signatures of broad metabolic classes, LC-MS in combination with PCA and PLSR allowed the identification of betaine lipids (BL) as potential biomarkers of nitrogen enrichment. A compound tentatively identified as monoacylglycerol-(N,N,N trimethyl)-homoserine (MGTS) showed the strongest positive relation to increasing wet nitrogen deposition regimes and consequent phosphorus deficiency. In contrast, the structurally related phosphatidylcholine containing a C18:2 ester showed the opposite trend in natural populations of C. portentosa. Results obtained for C. portentosa collected from the N manipulation site Whim Moss indicated that ammonium is causal for the increase of two of the identified betaine lipids in natural populations in C. portentosa. Betaine lipids as well as the phosphatidylcholine biomarker could potentially be used to monitor nitrogen regimes and resulting phosphorus limitation on the lichen C. portentosa. The approach used for this study represented an effective integration of the complementary analytical techniques of FTIR and LC-MS in combination with multivariate statistical tools for environmental metabolomic studies.

Dissolved organic nitrogen (DON) represents a major pool of fixed, reactive nitrogen in marine systems. It is now recognized that this pool can support primary production and the ability of some algal species to exploit DON compounds as sources of Nitrogen (N) may indicate that specific DON components can exert selective pressure on the composition of the phytoplankton community. In this study the ability of monocultures of ecologically-relevant algal species from the English Channel (Emiliania huxleyi, Micromonas pusilla, Alexandrium minutum and Chaetoceros peruvianus) to grow with DON as the only N source was examined using different artificial media. Among the two tested artificial seawater recipes, Aquil* was preferred as it contained lower micronutrient concentrations, and gave better growth results for all used species. In order to constrain the DON uptake to algae alone, a method for bacterial removal was tested using antibiotic additions. Both Slocombe antibiotic mixture (Cefotaxime-Carbenicillin-Kanamycin-AugmentinTM) and Penicillin-Streptomycin-Neomycin used were effective and not toxic to the algae. Incubation with the antibiotic up to 48 hours and a transfer period into antibiotic-free medium after 72 hours proved to be effective. However, the treatment removed bacteria in A. minutum cultures only; further treatment would be required for the other species to be cultured axenically. The ability to use DON was tested for the above mentioned species using the amino acid L-Arginine (ARG) as the sole N source, and growth was compared with nitrate-containing cultures of the same species. All the selected species grew in both NOᴈ‾ and in ARG, reaching lower final densities when incubated with ARG, although these were not significant. This study has shown that E. huxleyi, A. minutum, M. pusilla and C. peruvianus can grow on organic N, either by direct or indirect uptake, and develop comparable biomasses to species using inorganic N. Both C. peruvianus and M. pusilla cultures contained dissolved ammonium at the end of the experimental period, indicating potential indirect use by the algae of organic N converted to inorganic N by bacteria. A. minutum grew in the presence of ARG along with the cosmopolitan E. huxleyi; N-demand estimates, based on the molar concentration of N-ARG consumed, correlated with the final cell density, indicating that the species did not develop on inorganic N produced from ARG mineralisation, but directly on the ON substrate. Since A. minimum has been linked to harmful algal blooms, and E. huxleyi contributes significantly to oceanic CaCOᴈ deposition, their ability to utilise DON has environmental consequences in addition to the oceanic N-budget. Climate change scenarios predict both episodic conditions of elevated rainfall and extended periods of dry conditions leading to variable riverine inputs to coastal areas, altered nitrogen to phosphorus (N:P) ratios, and changes in the inorganic to organic balance of the nutrient pools. Organic N can constitute up to 69 % of the total N pools, respectively, making it crucial, to understand the cycling of this fraction in coastal waters, and how changes in the composition of nutrient pools could impact on marine ecosystem function and health.

Bibliography: leaves 183-202

No description available.

Graduation date: 2001

The objectives of this work were to evaluate the vegetative parameters used to estimate crop N demand and to estimate the accuracy and precision of the conceptual model of fertilization using an error propagation method. Corn plants were collected throughout the entire crop life cycle to determine the fresh and dry weight of the aboveground biomass and roots, root index, plant height, and corn grain yield. Three experiments were conducted, two under field conditions and one under greenhouse conditions. In the first field experiment in 2002, three sites were selected. The first site was the Texas A&M University (TAMU) Agricultural Experiment Station Research Farm in which a Ships clay soil was used. The second site was a cooperative farmer's land on a Weswood silt loam soil in Burleson County. These first two sites used Pioneer 32R25 as the corn hybrid. The third site was also a Ships soil in the TAMU Farm, but Dekalb 687 was the corn variety. In 2003, the second experiment was on a Ships soil in the field of TAMU Farm, and the third experiment was conducted in a greenhouse using Ships and Weswood soil. No differences in the root index and harvest index were observed, even when the Dekalb 687 hybrid was included. Variations in plant N concentration, moisture content, and yield were noted, but followed predictable patterns with time over the season. These parameters were consistent throughout the entire life cycle of the crop. The linear relationship between the fresh weight of aboveground biomass and fresh weight of roots was R2 = 0.92, the moisture content of corn plants over time was fit to a second grade polynomial with R2 = 0.98, and plant N content had a close linear relationship (R2=0.90) with the total plant dry weight, including roots, at harvest. The accuracy of the conceptual model was low under field conditions (55%), but high under greenhouse conditions (90%). Precision of the conceptual model was low both in the field (194%) and the greenhouse (115%) conditions.

High levels of soil nitrogen (N) can interfere with N2 fixation of lentil (Lens culinaris) and have variable effects on growth, yield and maturity of this indeterminate crop in Saskatchewan. In a series of field and greenhouse experiments during 2006 to 2008, response of the above-ground biomass (DW), plant N, N2 fixation, yield and days to maturity (DTM) of lentil to different N sources, time of N availability, and also to two no tillage (NT) durations were studied. First, eight cultivars of lentil were grown under three fertility treatments of granular rhizobium inoculant, 50 kg N fertilizer ha-1 and a non-treated control in three environment-years at Saskatoon and Indian Head, SK. The fertility treatments, plant N status and N2 fixation did not alter lentil DTM, but weather did. On average, lentil matured 101 and 84 days after seeding with sufficient rain and with drought, respectively. Growth and yield of the lentil were identical in the inoculant and the N fertilizer treatments. The N fertilizer treatment occasionally restricted N2 fixation, but N shortage was compensated via more N uptake from soil. The greatest N accumulation of lentil occurred during podding to maturity and benefitted pod N content. By maturity, pod, stem and leaf had 60, 24 and 14% of total dry matter and 78, 9 and 13% of total plant N, respectively. Leaf N concentration, which closely resembled soil and plant N status, was reasonably predicted by SPAD chlorophyll meter observations after pod set. Yield of five lentil cultivars was tested for the effects of 25-years (LN) versus 5-years (SN) of no tillage in the Black Soil Zone at Indian Head, SK in 2006, 2007 and 2008. In the same location, CDC Sedley was grown with four N fertilizer rates at the both LN and SN. Under terminal drought in 2006, average DW, N content and yield of the lentil cultivars in SN were greater than in LN, likely because of inhibited N2 fixation by the amplified soil N in the LN. In this year, 60 kg N fertilizer ha-1 reduced the yield difference of CDC Sedley in SN and LN. Lentil yield was identical or tended to be greater in LN than in SN with more rain in 2007 and 2008 that prolonged N mineralization and N uptake. In the greenhouse study, applying N fertilizer from flowering until podding and until maturity increased DW, N content and yield, and delayed maturity of lentil compared to lentil relying on N2 fixation. Later flowering of one cultivar or greater N2 fixation in one soil medium diminished the variation of inoculated lentil with the post-flowering N treatments, suggesting N fixation could supply lentil N requirement. Large-seeded cultivars produced greater yield than the small-seeded cultivars across environments in the fertility treatment study. Cultivar CDC Milestone produced comparable yield to high-yielding cultivars CDC Plato and CDC Greenland, but matured earlier. This cultivar showed promising results under both cool-wet and drought conditions. In contrast, CDC Sedley had lower on N2 fixation and HI values across the experiments. In the Black Soil Zone, CDC Milestone and CDC Robin performance was improved by improved HI and N2 fixation. Overall, results of this thesis do not support the application of N fertilizer for inducing early maturity in lentil. Soil inoculation with commercial strains is suggested for Saskatchewan cropping systems. Applying N fertilizer is not required, unless soil test results suggest otherwise. In places like Indian Head, SK, cultivars with greater N2 fixation and higher HI can better fit the short growing season, cool temperature and high soil N content.

High levels of soil nitrogen (N) can interfere with N2 fixation of lentil (Lens culinaris) and have variable effects on growth, yield and maturity of this indeterminate crop in Saskatchewan. In a series of field and greenhouse experiments during 2006 to 2008, response of the above-ground biomass (DW), plant N, N2 fixation, yield and days to maturity (DTM) of lentil to different N sources, time of N availability, and also to two no tillage (NT) durations were studied. First, eight cultivars of lentil were grown under three fertility treatments of granular rhizobium inoculant, 50 kg N fertilizer ha-1 and a non-treated control in three environment-years at Saskatoon and Indian Head, SK. The fertility treatments, plant N status and N2 fixation did not alter lentil DTM, but weather did. On average, lentil matured 101 and 84 days after seeding with sufficient rain and with drought, respectively. Growth and yield of the lentil were identical in the inoculant and the N fertilizer treatments. The N fertilizer treatment occasionally restricted N2 fixation, but N shortage was compensated via more N uptake from soil. The greatest N accumulation of lentil occurred during podding to maturity and benefitted pod N content. By maturity, pod, stem and leaf had 60, 24 and 14% of total dry matter and 78, 9 and 13% of total plant N, respectively. Leaf N concentration, which closely resembled soil and plant N status, was reasonably predicted by SPAD chlorophyll meter observations after pod set. Yield of five lentil cultivars was tested for the effects of 25-years (LN) versus 5-years (SN) of no tillage in the Black Soil Zone at Indian Head, SK in 2006, 2007 and 2008. In the same location, CDC Sedley was grown with four N fertilizer rates at the both LN and SN. Under terminal drought in 2006, average DW, N content and yield of the lentil cultivars in SN were greater than in LN, likely because of inhibited N2 fixation by the amplified soil N in the LN. In this year, 60 kg N fertilizer ha-1 reduced the yield difference of CDC Sedley in SN and LN. Lentil yield was identical or tended to be greater in LN than in SN with more rain in 2007 and 2008 that prolonged N mineralization and N uptake. In the greenhouse study, applying N fertilizer from flowering until podding and until maturity increased DW, N content and yield, and delayed maturity of lentil compared to lentil relying on N2 fixation. Later flowering of one cultivar or greater N2 fixation in one soil medium diminished the variation of inoculated lentil with the post-flowering N treatments, suggesting N fixation could supply lentil N requirement. Large-seeded cultivars produced greater yield than the small-seeded cultivars across environments in the fertility treatment study. Cultivar CDC Milestone produced comparable yield to high-yielding cultivars CDC Plato and CDC Greenland, but matured earlier. This cultivar showed promising results under both cool-wet and drought conditions. In contrast, CDC Sedley had lower on N2 fixation and HI values across the experiments. In the Black Soil Zone, CDC Milestone and CDC Robin performance was improved by improved HI and N2 fixation. Overall, results of this thesis do not support the application of N fertilizer for inducing early maturity in lentil. Soil inoculation with commercial strains is suggested for Saskatchewan cropping systems. Applying N fertilizer is not required, unless soil test results suggest otherwise. In places like Indian Head, SK, cultivars with greater N2 fixation and higher HI can better fit the short growing season, cool temperature and high soil N content.

Twenty-four Quarter horse weanlings (120 d +/- 10 d) were blocked by age into 4 groups (n = 6) for a 56 d trial to evaluate the influence of methionine on growth and nitrogen retention. Weanlings were housed by block and individually fed 1 of 4 concentrate diets twice daily at 1.5% BW (as fed). Weanlings were randomly assigned to 1 of 4 treatments: basal (0.20 MET), basal + 0.03% methionine (0.23 MET), basal + 0.07% methionine (0.27 MET), and basal + 0.11% methionine (0.31 MET). Diets were formulated to be isonitrogenous, isocaloric, and contain equal amounts of LYS and THR. Coastal bermudagrass hay was individually fed at 0.75% BW (as fed). Growth measurements, body weight, rump fat, and plasma were obtained every 7 d. The final 4 days consisted of total collection of urine and feces. Feed, fecal, and urine samples were analyzed for nitrogen content and nitrogen balance was calculated. Urine was analyzed for urea and ammonia concentration. Plasma was analyzed for urea concentration. Grain, hay, and fecal samples were analyzed for nutrient composition. Data were analyzed using the PROC MIX procedure of SAS. Linear, quadratic, and cubic effects were tested in the form of contrasts. There was no influence of treatment on growth measurements, nitrogen balance, or urinary urea or ammonia. Intake of LYS and THR (g/d) did not differ among treatments (P = 0.78 and P = 0.38 respectively). Plasma urea nitrogen (PUN) was influenced by treatment (P = 0.005) exhibiting quadratic (P = 0.04) and cubic (P = 0.002) effects. An unexpected peak in PUN was observed with 0.27 MET. Upon analysis, 0.20 MET contained more lysine than formulated, and 0.27 MET contained the least lysine. Treatments 0.20 MET and 0.31 MET contained more threonine compared to formulations. These differences may explain unexpected values of PUN concentration. Results suggest future studies that more closely isolate methionine as the only dietary variable are necessary to better explain the methionine requirements of weanling horses.