Long term management of lodgepole pine depends, in part, on the nutrient capital of the site. Harvesting has been shown to increase the availability of nitrogen and other nutrients for a limited period of time. This increase, or nutrient flush, following cutting has been attributed to several factors including changes in organic matter quantity and quality, soil moisture and temperature regimes, and competition for nutrients. Knowledge of the duration and the magnitude of the nutrient flush would be valuable for management decisions. A consequence of lodgepole pine clearcuts was studied for soil nitrogen availability and microclimate. Mineral soil and forest floor samples were anaerobically incubated and analyzed for ammonium-nitrogen (ppm). The mineral soil showed a flush lasting about 12 years, peaking by year 8, while the forest floor material showed no trend. The size of the increase from year 2 to year 8 was about 52%. Temperature (air and soil), soil moisture, solar radiation, and precipitation data were collected, and a soil water budget was calculated using a simple water balance model. The average calculated soil water deficit was 119 mm, but this may have been an over-estimate. Windrowing following cutting may have depleted the site nitrogen reserve which in turn reduced the amount that was mineralized during incubation. The interaction between the soil temperature and moisture may have further limited nitrogen availability to the lodgepole pine trees. It is concluded that the dynamics of nitrogen availability following clearcutting are important for the establishment and growth of lodgepole pine. The summer moisture deficit appears to limit the nitrogen mineralization rate as well as seedling growth. / Forestry, Faculty of / Graduate

It was the purpose of this investigation to present laboratory data concerning the assimilation of inorganic nitrogen by the aquatic actinomycetes. The strains of aquatic actinomycetes under consideration represented a cross section of those currently under culture at North Texas State University.

O nitrogênio é um elemento essencial à vida na Terra. Em geral, a disponibilização desse elemento para os seres vivos se dá por meio da fixação biológica do nitrogênio (FBN). Os micro-organismos capazes de realizar a FBN são denominados de diazotróficos e contêm o complexo enzimático da nitrogenase. Por ser um processo extremamente dispendioso, a FBN é regulada, principalmente em nível transcricional, em resposta à quantidade de nitrogênio fixado e aos níveis de oxigênio. Os mecanismos de regulação do processo em bactérias Gram-negativas estão bem caracterizados, porém, em bactérias Gram-positivas, os estudos ainda são escassos. Paenibacillus riograndensis SBR5T é uma bactéria Gram-positiva diazotrófica aeróbia facultativa e formadora de esporos, interessante modelo para o estudo da regulação da FBN com o genoma completo disponível. O fator de transcrição GlnR foi proposto como regulador dos genes nif em Paenibacillus spp. a partir de análises in silico. O presente trabalho identificou sítios de ligação de GlnR em promotores de genes envolvido com a FBN e validou o papel de GlnR como regulador negativo dos genes nif em P. riograndensis. Também foi demonstrado que a enzima glutamina sintetase interage com GlnR quando está inibida por feedback e estabiliza a ligação de GlnR às regiões reguladoras dos genes nif. Um modelo de repressão baseado em operadores múltiplos foi proposto integrando a regulação da FBN à regulação global do nitrogênio exercida por GlnR. Na tentativa de identificar elementos específicos relacionados à regulação do molibdênio (componente do cofator enzimático) e da nitrogenase alternativa (com cofator independente de molibdênio), foi acessado o perfil transcricional de P. riograndensis sob condições de limitação de nitrogênio e molibdênio. Alguns fatores de transcrição especificamente induzidos sob tais condições e provavelmente relacionados à homeostase de metais foram identificados. Com relação à glutamina sintetase, além da demonstração da interação entre a enzima e o fator de transcrição GlnR, duas proteínas adicionais homólogas de glutamina sintetase e que não participam dessa regulação foram identificadas codificadas no genoma. Uma delas foi caracterizada como glutamina sintetase funcional, enquanto a outra não apresentou atividade bioquímica. Além disso, um protocolo para transformação da linhagem em estudo foi estabelecido e otimizado, o que permitirá aprofundar os estudos de genética molecular tanto da FBN como de outros processos de interesse em P. riograndensis. / Nitrogen is an essential element for life. In general, it becomes available to biosphere mainly through biological nitrogen fixation (BNF). Microorganisms named diazotrophs perform BNF and they have the nitrogenase enzyme. As BNF is a very energetic expensive process, it is tightly regulated mainly at transcriptional level in response to available nitrogen and oxygen levels. Regulatory networks comprising BNF systems in Gram-negative bacteria are well characterized, while studies related to Gram-positive bacteria are scarce. Paenibacillus riograndensis SBR5T is a Grampositive endospore-forming facultative anaerobic diazotroph, whose complete genome sequence presents it as an interesting model for the study of BNF regulation. The transcription factor GlnR has been proposed as the nif regulator in Paenibacillus spp. based on in silico analysis. The present work identified GlnR-binding sites at BNFrelated promoters and validated GlnR role as nif negative regulator in P. riograndensis. It was also demonstrated that the feedback-inhibited glutamine synthetase enzyme interacts with GlnR and stabilizes its binding activity in the nif genes promoters. A multiple operator model was proposed to integrate BNF regulation and the global nitrogen regulation coordinated by GlnR. In an effort to identify specific regulatory elements related to molybdenum (enzymatic cofactor component) and the alternative nitrogenase (which presents a molybdenum-independent cofactor), the transcriptional profile of P. riograndensis was accessed under nitrogen and molybdenum limiting conditions. Transcription factors specifically induced under such conditions and probably related to metal homeostasis were identified. Regarding the glutamine synthetase, two additional glutamine synthetase homologs that do not take part in GlnR regulation were identified. One of them was characterized as a functional glutamine synthetase, while the other did not display biochemical activity. Also, a protocol to transform the model in study was established and optimized. This protocol allows the development of further molecular research to unveil BNF and other interesting processes in P. riograndensis.

In oligotrophic systems, where primary production is low and nitrogen is in short supply, nitrogen fixation process is intense. Although a few diazotrophs (eg. Trichodesmium) have been widely-studied, the rest of the diazotrophic community is still poorly understood. Furthermore, the global distribution of diazotrophs are yet to be clearly resolved. This dissertation assessed the distribution of diazotrophs in oligotrophic systems, particularly in the tropical and subtropical oceans, using genomics tools including next-generation sequencing. We first tested out a pair of nifH-specific primer that previously performed well in silico, but found that its application on seawater samples was biased towards paralogous, non-functional nitrogenase nifH genes. Instead, we found that the use of a nested PCR method using different primers sets to be more effective in amplifying functional nifH genes. Trichodesmium sp., UCYN-A and Pseudomonas sp. forms the core of the diazotrophic communities in oligotrophic oceans. Temperature is the primary driver of the abundances and distributions of these organisms in the Pacific, Atlantic and Indian Oceans, as well as in the oligotrophic Red Sea. Trichodesmium tends to dominate warm, surface waters, while UCYN-A prefers cooler environments and dwell in sub-surface waters in the Red Sea. Due to the dominance of Pseudomonas in the large-sized fraction samples, they are believed to be part of the Trichodesmium-associated consortia, although this requires further investigations. We also found non-cyanobacterial species of diazotrophs to be dominant previously-described hotspots of nitrogen fixation, and found evidence for the widespread of alternative nitrogenases (Cluster II). Using the Red Sea as an exemplar for future warming ocean, we found patterns of niche partitioning in the Red Sea diazotrophs, based on their distribution along seasons, latitude and depth. Our one-year observation of Red Sea Trichodesmium population witnessed the collapse of the population at temperatures above 32°C. This dissertation not only improve our understanding of the effects of future rising temperature on the natural populations of diazotrophs, but it also helps to establish a baseline understanding of the structure, spatial and temporal dynamics of Red Sea diazotrophs, which has not been discussed elsewhere.

Seagrasses are key coastal ecosystems, providing many ecosystem services. Seagrasses increase biodiversity as they provide habitat for a large set of organisms. In addition, their structure provides hiding places to avoid predation. Seagrasses can grow in shallow marine coastal areas, but several factors regulate their growth and distribution. Seagrasses can uptake different kinds of organic and inorganic nutrients through their leaves and roots. Nitrogen and phosphorous are the most important nutrients for seagrass growth. Biological nitrogen fixation is the conversion of atmospheric nitrogen into ammonia by diazotrophic bacteria. This process provides a significant source of nitrogen for seagrass growth. The nitrogen fixation is controlled by the nif genes which are found in diazotrophs. The main goal of the project is to measure nitrogen fixation rates on seagrass sediments, in order to compare among various seagrass species from the Red Sea. Moreover, we will compare the fixing rates of the Vegetated areas with the bare sediments. This project will help to ascertain the role of nitrogen fixing bacteria in the development of seagrass meadows.

Nitrogen use efficiency (NUE) and nitrogen (N) management practices have been an increasing concern among corn (Zea mays L.) producers. The objective of this study was to assess the placement distance of UAN and measure total N uptake on corn grain yield as affected by irrigation. Field trials were conducted in 2011 and 2012 at the Plant Science Research Center, Mississippi State, MS. Placement distance and irrigation influenced both total N uptake and grain yield results during both years of this study. Total N uptake and corn grain yield results were derived from plant samples and harvest data. Overall results from this study indicate increasing placement distance from the center of the planted row resulted in a decrease in total N uptake and grain yield. Results also show the subsurface banded treatment resulted in a greater N uptake and grain yield.

No description available.

No description available.

Sustainability of dairy production depends on their production of feed and finding ways to increase profitability through dairy production or even carbon (C) crediting and adding C inputs into the soil to sequester C. To increase farm profitability, dairy producers in Illinois, has intensified their feed production through integrating winter cereals such as winter cereal rye (Secale cereale) (WCR) into single season corn for silage (double cropping). Intensified cropping system allows for increased feed production, covering the soil year-round, and adding C inputs while minimizing nutrient loss mainly through runoff or leaching. Two management practices that improve the sustainability of corn silage – WCR double crop are harvesting date and nitrogen (N) management during the WCR phase of the production. This thesis has two main chapters. Chapter 1 evaluates the effect of harvesting date (five weekly harvest from late-March to early-May) with and without optimum N addition (0 vs. 47 kg N ha-1). Our objective was to evaluate harvesting date and spring N fertilization effect on WCR morphology, forage yield, nutrient removal, and quality. A quadratic model best explained an increase in WCR biomass in response to GDD (growing degree days) accumulation (R2 = 0.81). Increase in GDD linearly decreased WCR relative forage quality (RFQ). Benchmarking RFQ at 150 for dairy milk production indicates that WCR should be harvested at a GDD of 543 at which WCR plant height was 31.8 cm and dry matter (DM) biomass was 0.77 Mg ha-1. Benchmarking RFQ at 125 for heifer production indicated that harvest should occur at a GDD of 668 at which the WCR was 71 cm tall and its DM yield was 2.25 Mg ha-1. Nitrogen balances were negative at the no-N control treatment indicating a need for some N to maximize WCR yield. We found that a rate between 21 and 42 kg N ha-1 maximizes yields reflecting on slightly positive balances. Our results suggest that harvesting date can be predicted by GDD and should be adjusted for RFQ. We conclude that smaller than 42 kg N ha-1 N fertilizer is required for WCR production in soils with manure history and high soil organic matter (>30 g kg-1). Chapter 2 hypothesized that N fertilization of WCR as cover crop can increase nutrient recycling and C sequestration which offers C trading benefits to growers. We evaluated the effects of N fertilizer application in fall (0 vs. 56 kg N ha-1), and N fertilizer rates in spring (0, 23, 47, and 71 kg ha-1) on WCR dry matter (DM) biomass and cover crop quality. Results indicated that fall N fertilization had no effect on WCR biomass or quality reflecting on loss of applied N in the fall. Spring N application did not affect WCR biomass yield but increased N, P, and K concentrations, their uptake, C concentration, and decreased C:N and lignin:N ratios. We concluded that only spring N fertilization improves WCR cover crop benefits. Overall, we suggest that for high-quality forage, (RFQ at 150) WCR should be harvested at a GDD of 543 at which WCR plant height was 31.8 cm and dry matter (DM) biomass was 0.77 Mg ha-1. For RFQ of 125 (for heifer production), harvest should occur at a GDD of 668 at which the WCR was 71 cm tall and its DM yield was 2.25 Mg ha-1. Neither in fall nor in spring, N fertilization increase WCR C accumulation. Spring N fertilization reduces WCR C:N and lignin:N which are desirable for crop production.

No description available.