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Forests are sites for mercury deposition, where accumulation in aquatic environments can occur. Soil total mercury (THg), C and N to 15 cm were studied in ten seasonal pond basins in a northern hardwood forest (Minnesota, USA). Pools and concentrations of THg were lower in uplands than in ponds, indicating downslope transport or differential deposition. In uplands, THg concentrations were the same in 0-2 and 2-5 cm depths and then decreased, whereas density peaked in 2-5 cm, highlighting the importance of bulk density on mass. Carbon and N trends were similar to THg. Apart from pond centers, strong positive relationships between THg and C were observed. Upland slope length, graminoid cover, basin area and tree height accounted for over half of THg variance at pond edge. Understanding the distribution, trends and contributing factors of soil THg can further efforts toward immobilization and sequestration, thus minimizing the potential for bioaccumulation. / United States Forest Service / North Dakota State University

Magister Scientiae (Biodiversity and Conservation Biology) - MSc (Biodiv and Cons Biol) / Kingklip (Genypterus capensis) and monkfish (Lophius vomerinus) and are ecologically and economically important demersal fish species that are found along both the eastern and western parts of southern Africa’s coastline. Despite their commercial value, limited information exists focusing on the trophic ecology of these two species. This is the first study to make use of both stomach content analysis and stable isotope analysis to directly compare and examine the trophic ecology of G. capensis and L. vomerinus off the West and South coast of South Africa. / 2022

Soybeans are able to obtain nitrogen from two different sources, nitrogen found in the soil (e.g. from fertilizers) and biologically fixed nitrogen (from symbiotic bacteria called rhizobia). Nitrogen source and degree of reliance on N-fixation can impact plant nitrogen dynamics, which has the potential to impact above-ground herbivore performance. We examined the impact of nitrogen availability and rhizobial association on soybean aphid biology and reproduction in a series of greenhouse and field experiments. Aphid establishment on plants was not significantly affected in any experiment. However, aphid reproduction was significantly affected by rate of nitrogen fertilization, rhizobial inoculation, and type of rhizobial seed inoculant. In general, aphid densities were not correlated with plant parameters associated with plant nitrogen or N-fixation. Producers commonly use fertilizers and rhizobial seed inoculants, thus it is important to continue exploring the mechanisms underlying how plant nitrogen dynamics impact soybean insect pests.

Nitrogen-rich energetic materials (EMs) are characterized by their typically high values for heat-of-formation as well as the environmental benefit associated with the production of nitrogen gas upon detonation. This makes them the most likely class of materials to replace currently used explosives such as lead azide (LA), 2,4,6-trinitrotoluene (TNT), and 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX). The sensitivity of EMs to mechanical stimuli such as impact and friction is governed primarily by the packing arrangement, as observed in the crystal structure. For this reason, crystal engineering is the most effective tool to achieve low sensitivity, high-performing EMs. In Chapter 2 the pH-dependent formation of two different dihydrazinyl tetrazine/azobistetrazolate salts was explored. These materials have high calculated detonation parameters and are expected to have large differences in sensitivity based on the different packing arrangements adopted. In Chapter 3, azobistetrazolate was substituted for a series of more thermally stable anions for the creation of a family of dihydrazinyltetrazine-based secondary explosives. The use of oxalyldihydrazide (ODH) as an energetic cation was explored in Chapter 4, where the selective formation of both singly and doubly protonated versions of ODH allowed for the creation of both 1:1 and 2:1 energetic salts.

Wheat was grown hydroponically for 23 days ( early boot stage) in a controlled environment at NO3- concentrations of 100 and 1000 μ,M and CO2 levels of 360 and 1200 μ,mol mo1-1. Nitrogen consumption and transpiration were measured daily. Tissue nitrogen concentration, total biomass, and percent root mass were measured at harvest. Nitrogen recovery and nitrogen use efficiency were calculated. Elevated CO2 increased nitrogen consumption of the 100 μ,M NO3- treatment by 13.6% and the 1000 μ,M NO3- treatment by 21.3%. These increases were particularly evident during tillering and early grain fill. Whole plant nitrogen, shoot NO3-, and root NO3- concentrations were increased by elevated CO2. High CO2increased biomass by 15% and increased percent root mass by 11 %. Nitrogen recovery and nitrogen use efficiency were similar at both CO2 concentrations. Transpiration (L m-2ground d-1) decreased by 40% in elevated CO2. The 1000 μ,M NO3- treatment consumed more NO3- than did the 100 μ,M NO3- treatment (8.1% in ambient CO2, 15.5% in elevated CO2); this effect was most pronounced during the last 5 days of the experiment (flag leaf emergence and early grain fill). Percent root mass increased as N concentration decreased from 1000 to 100 μ,M. Nitrogen levels did not significantly affect tissue N concentration or biomass. Nitrogen losses increased as N supply increased; an average of 16% of the nitrogen added to the 100 μ,M NO3- treatment was lost, while the 1000 μ,M NO3- treatment lost 21%. Nitrogen use efficiency and transpiration were similar in both nitrogen treatments.

Urea based fertilizers are susceptible to N losses through volatilization, denitrification, and leaching. A field and incubation experiment were conducted at Mississippi State between 2013 and 2015 to evaluate the effect of fertilizer stabilizers on grain yield, N use, and N transformations in various soil textures. Stabilizers were applied to liquid urea-ammonium-nitrate (UAN) solution (32%) and granular urea (46-0-0) at labeled rates for 179 and 112 kg N ha-1 for the field and incubation experiments, respectively. Grain yield and N content at tasseling and physiological maturity were measured for the field experiment. Extracts from the incubation experiment were measured for NH4+-N and NO3⁻-N concentrations. Results from the field experiment suggest greater plant N accumulation, but inconsistent yield increases with fertilizer stabilizers. Incubation results indicate fertilizer stabilizers significantly decrease the rate of N transformations. Further research is necessary to determine the effects of stabilizers over N rates and yearly environmental conditions.

Rice (Oryza sativa L.) that is grown in the U.S. is predominantly grown in the mid-south. Current Mississippi State University recommendations for nitrogen (N) fertilization of rice suggest a single application of 168 kg N ha-1 on soils with CEC ¡Ü 20 and 202 kg N ha-1 on soils with CEC > 20. The primary objective was to identify alternative N management strategies that may potentially be used to reduce costs associated with aerial application of N fertilizer to rice. Research was established at the Delta Research and Extension Center, at Stoneville, MS, on two soil textures during 2015 and 2016. The combination of application timings and N sources resulted in a total of eight N management strategies. Data from all siteyears were pooled together for analysis to evaluate differences among N management strategy. Urea + [N-(n-butyl)thiophosphoric triamide] (NBPT) applied in a single application 7 days before flood (DBF), two-way split application, and PCU-2 LF produced statistically similar and greatest mean rice grain yield. These data suggests that N fertilizer can be applied early (2 to 3 leaf growth stage) from a ground based fertilizer spreader prior to the levee construction. Single optimum and two-way split N management strategies produced more total dry matter (TDM) at heading (HDG) and more N uptake at HDG. Urea + NBPT applied in a single application 7 DBF should be the N management strategy of choice in mid-southern U.S. rice production.

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