No description available.

Digitized by Kansas State University Libraries

Remarkably little is known about nitrogenous excretion in freshwater invertebrates. In the current study, the nitrogen excretion mechanism in the carnivorous ribbon leech, Nephelopsis obscura, was investigated. Based on gene expression analysis and Ussing chamber experiments, the skin was identified as a major site of ammonia excretion. Pharmacological experiments and enzyme assays suggested an ammonia excretion mechanism that involves the V-ATPase, Na+/K+-ATPase and carbonic anhydrase, but not necessarily a functional microtubule system. Most importantly, functional expression studies of the identified Rh-protein cloned from leech skin (NoRhp) revealed an ammonia transport capability of this protein when expressed in yeast. Exposure to high environmental ammonia (HEA) caused a new adjustment of body ammonia, accompanied with a decrease in NoRhp and Na+/K+-ATPase mRNA levels, but unaltered ammonia excretion rates. The results of this study showed many similarities to the ammonia excretion mechanisms proposed in the gills of freshwater fish. / May 2015

Increased deposition of nitrogenous compounds from the atmosphere may lead to the competitive dominance of aggressive grass species and reductions in species richness. This thesis aims to investigate the effects of atmospheric deposition of ammonia on species-rich limestone grasslands in the Cotswolds, and the role that management may have in modifying these effects. A field survey investigated species composition and quantified environmental variables including atmospheric ammonia concentration. Species richness and diversity were greatest on the more heavily grazed sites on deeper soils, but these diverse grasslands were composed of a high proportion of nitrophilic, competitive and ruderal species. No relationships between atmospheric ammonia and species composition were detected. The effects of grazmg and nitrogen on species composition were investigated by transferring turves between sites with contrasting atmospheric ammonia concentrations. Although grazed plots at the high ammonia site were of slightly higher diversity than grazed plots at the low ammonia site, these differences were reversed in fenced plots. In ungrazed plots, the development of a grass dominated, species-poor community was less pronounced at the low ammonia site, although the higher level of nitrophilic/competitive species here suggested that soil depth and soil phosphorous may also be important. A controlled greenhouse experiment investigated the effect of nitrogen addition and cutting on the competition between Brachypodium pinnatum and Bromopsis erecta. Above ground growth of both species was limited by nitrogen, although growth of B. erecta appeared to be limited by another resource at high densities. There was significant niche overlap between the two species, though cutting of high density pots reduced this niche overlap. The two grasses were equally matched in competitive ability, and neither treatment had any clear effect on the outcome of competition. The tillering response to cutting was greater in B. pinnatum than in B. erecta, although nitrogen addition increased tiller production by B. erecta. The effects of nitrogen addition and cutting treatments on nine grassland species was investigated in a greenhouse experiment. Nitrogen addition had no significant effects, but cutting reduced the above ground biomass of B. erecta and B. pinnatum and increased the above ground biomass and size of most of the other species. It is concluded that atmospheric ammonia deposition appears relatively unimportant in determining the species composition of species rich grasslands. However, experimental addition of nitrogen may increase grass growth, and grass dominance in the field can lead to reductions in species richness. In grazed grasslands, grasses may become more grazing resistant under conditions of enhanced nitrogen availability. However, phosphorous may be an important factor modifying the effects of enhanced nitrogen deposition.

No description available.

No description available.

4 pp. / Originally published: 2001 / Nitrogen (N) is the nutrient that is required most consistently and in larger amounts than other nutrients for cotton production. Common rates of fertilizer N applied in Arizona cotton production systems range from 50 to over 300 lbs N/acre. The management of fertilizer N is critical, both for insuring optimum cotton yields, and minimizing the potential for environmental contamination.

The expansion of mesquite (Prosopis velutina) in southeastern Arizona and attempts to control or remove mesquite have been well documented. However, removal of woody plants may affect the distribution and quantities of nutrient resources within soil including changes in carbon (C) and nitrogen (N) cycling and changes in the amounts of C and N sequestered in these soils. We hypothesized that mechanical mesquite removal would alter soil microclimate and nutrient inputs, leading to changes in soil C and N cycling and microbial communities and activities.This study was conducted at two separate semi-arid grassland sites south of Tucson, AZ during a three-year period. There were six study plots at each site, three plots from which mature mesquite trees had been mechanically removed and three plots where mature mesquite trees were left intact. We measured the soil temperature and moisture, C and N pools, N2O and CO2 fluxes, N mineralization rate, and microbial resistance and resilience to determine if short term changes in any of these parameters were taking place.No significant differences in N mineralization rate or microbial resistance or resilience were found between the soils under intact mesquite and from plots where mesquite had been mechanically removed. Soil temperature was not statistically analyzed because temperature was taken in only one plot per treatment and without within-treatment replicates, t-tests could not be performed. Statistically significant differences in soil moisture, total soil C and N, microbial biomass C and N, heterotrophic plate counts, and CO2 and N2O fluxes were found between treatments on different dates throughout the experiment. Despite this finding of some significant differences between treatments for some parameters measured, no recognizable pattern of changes was observed during this study. Over the course of the experiment, the data did not support our overall hypothesis, that short term changes in microclimate following mesquite removal would alter soil C and N cycling and microbial communities and activities.

No description available.

No description available.