The role of arbuscular mycorrhizal fungi in prairie wetlands

Research on arbuscular mycorrhizal fungi (AMF) suggests that their effect on plant growth is a continuum that changes from positive to negative along environmental gradients as conditions for plant growth improve. Prairie wetlands were used to test this mycorrhizal continuum model. First, three saline and three freshwater wetlands were surveyed for AMF, to investigate the hypothesis that AMF colonization would be greater in wetlands with high soil salinity, lower nutrient levels, and during periods of drought. Second, a greenhouse experiment on Carex stricta and Calamagrostis canadensis tested whether AMF improved plant growth and nutrient uptake under five hydrologic regimes. Third, another greenhouse experiment tested whether AMF improved the competitive ability, productivity, and macronutrient uptake of the facultative mycotroph, C. stricta, along nutrient and soil moisture gradients while growing with Phalaris arundinacea and Typha latifolia;AMF colonization in Iowa and North Dakota ranged from 0.2 to 72% among all plant species and was strongly dependent on the plant host regardless of environmental factors or the plant\u27s life stage. Colonization was greatest at the peak growing and fruiting period (June) on many early season grasses and sedges. AMF colonization was also greater in plants growing in the poor soil conditions found in North Dakota--low phosphorus and high soil pH. Soil moisture did not have a significant effect on AMF colonization. However, the survey was done in a wet year and may have underestimated the importance of soil moisture on AMF colonization. AMF colonization levels measured in the field supported the mycorrhizal continuum model;High soil phosphorus levels in the hydrology experiment probably prevented AMF colonization of C. stricta and C. canadensis. The lack of AMF colonization suggests that mycorrhizae are not important to these plants growing in natural wetlands with high soil phosphorus levels, even in dry conditions. Non-mycorrhizal fungi reduced biomass of C. canadensis, but not C. stricta, indicating that C. stricta may have antifungal properties;Nutrient levels and interspecific competition explained 35% of the total variation on C. stricta productivity and macronutrient concentration, whereas soil moisture explained only 7% and AMF 0% of the variation. AMF did not increase the competitive ability, productivity, or nutrient uptake of C. stricta

The relationship between risk and the respondent\u27s level of socialization in the military

The following thesis deals with a sensitive issue, namely the examination of risk-taking behaviors in a military context. Generally, it is agreed that certain decisions made by the military are considerably more vast and important (in terms of the sociopolitical, and moral ramifications) than decisions reached by non-military groups. In light of this agreement, any analysis of risk-taking behavior could be interpreted as threatening to the image of the military. Understanding the sensitivity of the central theme of the following thesis demands an understanding of the assumptions of the investigation. The two major assumptions of this work are: a) the military is not a mindless, thrill-seeking entity lacking in rational restraint, but the military socialization process does seem to elicit risk y behaviors from its members; and b) the military risk ethic is not necessarily any more dramatic than the civilian risk ethic, even though this relationship has not been tested in the literature of group behaviors. I am not, in other words, launching an attack on the rationality of military decision-making. With the above mentioned assumptions in mind, the analysis of socialization and risk in a military context will be developed throughout the following thesis

Investigating the influence of firm characteristics on the ability to exercise market power : a stochastic frontier analysis approach with an application to the iron ore market

This paper empirically analyzes the existence of market power in the global iron ore market during the period 1993-2012 using an innovative Stochastic Frontier Analysis approach introduced by Kumbhakar et al. (2012). In contrast to traditional econometric procedures, this approach allows for the estimation of firm- and time-specific Lerner indices and, therefore, the assessment of the influence of individual firm characteristics on the ability to generate markups. We find that markups on average amount to 20%. Moreover, location and experience are identified to be the most important determinants of the magnitude of firm-specific markups

Uptake of dissolved inorganic and organic bphosphorus compounds by phytoplankton and bacterioplankton

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109807/1/lno19923720232.pd

Toughening and Mechanical Properties of Epoxy Modified with Block Co-polymers and MWCNTs

AbstractThe objective of this work was to systematically develop and understand novel polymeric hybrid nanocomposites that include block copolymers (BCP) with tailored morphologies in order to generate high toughness. Furthermore, rigid fillers in the form of multi-walled carbon nanotubes (MWCNT) were added systematically together with block copolymers to study the combined effect of rigid nanofillers and more ductile BCP particles. The resulting matrix was extensively and carefully characterized by standard methods. This included thorough characterization of mechanical, fracture mechanical and thermal properties. Results show that both fracture toughness, KIc, and critical energy release rate, GIc, were increased linearly to a maximum of 2.10 MPa.m1/2 and 1.46 kJ/m2 respectively by the addition of 12 wt. % BCP. Fractography studies reveal toughening mechanisms of the nanocomposites that were identified as both the cavitation of spherical micelles and enhanced plastic deformation and furthermore fiber pull-out in the case of hybrid nanocomposites