Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (leaves 82-126).

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Thesis (B.S. in Ag.)--Cornell University, 1907.

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During the course of this research an instrument utilising combustion as a means of gas extraction capable of N, e, Ar and He analysis has been developed and the entire analytical procedure has been automated. N and e isotopic analysis has been performed on eclogitic and peridotitic diamonds (mainly from Yakutian kimberlites and the Roberts Victor kimberlite pipe). Diamonds with unusual (light and heavy relative to the peak of ol3e distribution of mantle diamonds) carbon isotopic signatures were considered for the research so that diamonds in the range of δ¹³C from -30‰ to + 2.8‰ were characterised for δ¹⁵N. The results together with data obtained previously by the others define fields for eclogitic and peridotitic diamonds on a plot of δ¹⁵N vs. δ¹³C. The model of mantle nitrogen and carbon evolution is discussed. A comprehensive comparison between carbonado and other known forms of microcrystalline diamond (framesites and shock diamonds) has been made for a number of parameters: N and e isotopic composition and N content; 4He content; morphology of the inner structure of diamond aggregates. It can be concluded that carbonado is generally similar to frame sites and all facts known about carbonado can be explained on the grounds of common mantle origin involving subducted carbon and nitrogen. Since extremely high 4He concentrations are encountered in carbonado this parameter is considered to be the most singular feature of this diamond variety and the radial distribution of 4He in single diamond crystals has been studied. A 4He content comparable with that in carbonado was found in the 30 J.lm skin of diamond crystals (up to 1.4 x 10⁻²) suggesting that carbonado could acquire high 4He concentration in the same geological processes as single diamond crystals and making carbonado indistinguishable from mantle diamonds in terms of He content. An additional result of the investigation is that the maximum of 4He diffusion coefficient for diamond at mantle P,T conditions can be estimated (≈4x10⁻²¹ ) from the 4He zoning identified in the interior of a diamond crystal from the Finsch kimberlite. A number of diamonds of impact origin from Popigai crater and Ebeliakh river placer deposits were studied for N, C and Ar isotopic compositions. It was concluded that diamonds from these two localities have resulted from separate impact events and that diamond aggregates studied are most probably consist of a mixture of different Ar and N carriers (e.g. two types of diamond grains).

Global changes resulting from human activities, including elevated levels of greenhouse gases, enrichment of nitrogen and land use changes, have led to substantial losses in biodiversity of macroscopic organisms, such as plants and animals, but whether these changes will have similar impacts on microscopic organisms, such as bacteria and fungi, is less clear. I examined the impact of three of these global changes, including elevated carbon dioxide, increased soil nitrogen availability and large-scale deforestation, on the biodiversity of soil fungi in three separate ecosystems. The responses of fungi to global changes were variable across ecosystems and the experimental system and were not readily predicted by observed changes in the plant community. However, subtle shifts in the community composition of fungi were observed in response to all global changes. Whether these shifts will impact the ecosystem function of these systems in unclear, but previous studies suggest that even small changes in community dynamics can have large effects on important processes, such as nitrogen cycling and carbon storage. These findings indicate that soil fungi do respond to global changes, but additional research must be undertaken to examine the effects of these shifts. / 10000-01-01

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Master of Science / Department of Agronomy / Ignacio Ciampitti / Soybean [Glycine max (L.) Merr.] yields have continuously increased over time. Seed yields are determined by the genotype, environment, and management practices (G × E × M) interaction. Closing yield gaps require a continuous improvement in the use of the available resources, which must be attained via implementation of better management decisions. Linear relationships between seed yield and nitrogen (N) demand are reported in the scientific literature. Main sources of N to the plant are the biological N fixation (BNF) and the soil mineralization processes. On overall, only 50-60% of soybean N demand is met by the BNF process. An unanswered scientific knowledge is still related to the ability of the BNF to satisfy soybean N demand at varying yield levels. Seed N demand not met by N fixation plus soil mineral N, is then fulfilled by the remobilization of N from vegetative organs during the seed filling period. An early remobilization process reduces the photosynthetic activity (leaves) and can limit seed yield. The objectives of this project were to: i) study yield improvements and contribution of N via utilization of contrasting N conditions under historical and modern soybean genotypes, and ii) quantify main seed N sources during the seed filling period. For objective one, four field experiments were conducted during the 2016 and 2017 growing seasons in Kansas, United States (US) and Santa Fe Province, Argentina (ARG). Those experiments investigated twenty-one historical and modern soybean genotypes with release decades from 1980s to 2010s. As for objective two, three field experiments were conducted during the 2015 and 2016 growing seasons in Kansas, US, studying three soybean genotypes: non-roundup ready (RR), released in 1997; RR-1, released in 2009; and RR-2, released in 2014. Across all studies, seeds were inoculated and tested under three N management strategies: i) control without N application (Zero-N); ii) 56 kg N ha-1 applied at reproductive growth stages (Late-N); and iii) 670 kg ha-1 equally split at three timings (Full-N). As for yield improvements and N limitation, soybean yield improvements from the 1980s to 2010s were documented, representing 29% increases in the US and 21% in ARG. Regarding N management, the Full-N fertilization produced a 12% increase in seed yields in the US and 4% in ARG. As for main seed N sources in objective two, remobilization accounted for 59% of seed N demand, and was negatively related to new N uptake occurring during the seed filling period. Seed N demand for greater yields was dependent on both, N remobilization and new N uptake, while for lower yields, seed N demand was mainly supported by the N remobilization process. These results suggest that: a) high seed yields are somehow limited by the availability of N to express their potential, although the question about N application still remains to be fully investigated, as related to the timing and the environment by plant interactions that could promote a N limitation in soybeans; b) remobilization accounts for majority (59%) of N sourced to the seed, and c) high yielding soybean (modern genotypes) rely on diverse N sources: the N remobilization process plus new uptake of N.

A balanced nitrogen (N) cycle is paramount for the ecology and biogeochemistry of planet Earth. Human activities are now causing an imbalance in the N cycle, with several negative effects on the marine environment. However, our knowledge of the marine N cycle remains incomplete, especially with regards to the role of dissolved organic N (DON). Therefore, there is need to study the role of DON more extensively to aid in restoring balance to Earth's ecosystems and biogeochemical cycles. This project investigated DON dynamics and influence on phytoplankton in coastal and shelf seas (CSS) to the west of Britain where DON was understudied. First, selected methods for the measurement of N uptake rates, urea and dissolved free amino acid (DFAA) concentrations were reviewed and tested. Then, they were used to study the spatial and temporal DON dynamics in the shelf region to the west of Britain (Irish Sea and adjacent shelf), the in-situ seasonal DON dynamics and N uptake in relation to phytoplankton community composition and abundance in Loch Creran, and the influence of DON on the phytoplankton community composition and abundance in controlled nutrient uptake kinetics and growth experiments and ecosystem modelling. The main findings were: DON was important in the N dynamics of the Irish Sea and adjacent shelf waters; DON was correlated with changes in phytoplankton community composition in Loch Creran; its seasonal cycle suggested its importance as an N source for the development of the spring bloom; these ideas were further supported by controlled laboratory experiments and ecosystem modelling.

13 pp. / A nitrogen fertilizer study was conducted in order to determine the effect of N rates on forage sorghum yield and quality and to develop tissue testing guidelines for fertilizer application to forage sorghum. The study was conducted at the University of Arizona Maricopa Agricultural center on sandy clay loam soil irrigated using the flood method. Forage sorghum was fertilized with six N rates varying from 0 to 250 lb N/acre in 50 lb N/acre increments. The whole plant, lower stem, and most recently expanded leaf were sampled five times during the growing season and analyzed for N content in order to establish tissue N guidelines for fertilizer application. The plant part that was most sensitive to N fertilizer application and plant N status was lower stem. Leaf and plant N levels were not affected by fertilizer application. The stem nitrate and stem N tests were able to identify N deficient plants very early in the season, long before plant growth was affected by the N deficiency, unlike leaf and plant N. Forage yield at final harvest fitted to a quadratic function was maximized at the 250 lb N/acre N rate. However, the yield increase with any amount of fertilizer did not pay for the cost of the fertilizer and the most economical N rate for yield was no N fertilizer applied at all. In terms of milk per acre, the maximum was achieved at 150 lb N/acre, and the economic optimum in terms of milk was slightly less than this amount of fertilizer.