University of Arkansas

About: University of Arkansas is a education organization based out in Fayetteville, Arkansas, United States. It is known for research contribution in the topics: Population & Poison control. The organization has 17225 authors who have published 33329 publications receiving 941102 citations. The organization is also known as: Arkansas & UA.

An essay on synthetic chemistry of colloidal nanocrystals

Abstract: The central goal of synthetic chemistry of colloidal nanocrystals at present is to discover functional materials. Such functional materials should help mankind to meet the tough challenges brought by the rapid depletion of natural resources and the significant increase of population with higher and higher living standards. With this thought in mind, this essay discusses the basic guidelines for developing this new branch of synthetic chemistry, including rational synthetic strategies, functional performance, and green chemistry principles.

Wheat Stripe Rust Epidemics and Races of Puccinia striiformis f. sp. tritici in the United States in 2000.

Abstract: Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici, is most destructive in the western United States and has become increasingly important in the south-central states. The disease has been monitored by collaborators through field surveys and in disease nurseries throughout the United States. In the year 2000, stripe rust occurred in more than 20 states throughout the country, which was the most widespread occurrence in recorded history. Although fungicide applications in many states reduced yield losses, the disease caused multimillion dollar losses in the United States, especially in Arkansas and California. One of the prevalent cultivars, RSI 5, had a yield loss of about 50% in the Sacramento-San Joaquin Delta region of California. In the Pacific Northwest, wheat losses due to stripe rust were minimal because cultivars with durable resistance were widely grown and the weather in May 2000 was not favorable for the disease. To identify races of the pathogen, stripe rust collections from 20 states across the United States were analyzed on 20 wheat differential cultivars, including Clement (Yr9, YrCle), Compair (Yr8, Yr19), and the Yr8 and Yr9 near-isogenic lines. In 2000, 21 previously identified races and 21 new races were identified. Of the 21 new races, 8 were pathotypes with combinations of virulences previously known to exist in the United States, and 13 had virulences to one or more of the lines Yr8, Yr9, Clement, or Compair. This is the first report of virulence to Yr8 and Yr9 in the United States. Most of the new races were also virulent on Express. Races that are virulent on Express have been identified in California since 1998. The races virulent on Yr8, Yr9, and Express were widely distributed in California and states east of the Rocky Mountains in 2000. The epidemic in 2000 demonstrates that increased efforts to breed for stripe rust resistance are needed in California, the south-central states, and some other states in the Great Plains. Diversification of resistance genes and use of durable resistance should prevent large-scale and severe epidemics.

Effects of native grazers on grassland N cycling in Yellowstone National Park

Abstract: We investigated the effects of native ungulates on grassland N cycling in Yellowstone National Park by examining natural '5N abundance (815N) of soils and plants inside and outside long-term (32-36 yr) exclosures. Across six topographically diverse sites, grazers increased W5N of soil (0-20 cm) by 0.7%o, which was substantial considering that values for ungrazed soil ranged 2.4%o (2.4-4.8%o). The magnitude of grazer '5N en- richment was positively related (r2 = 0.70) to the intensity of herbivore activity during the study, indexed by the amount of dung (g/m2) deposited at the sites. We also found that soil W5N of ungulate urine and dung patches was significantly higher than that of control areas. Grazers probably increased soil W5N by promoting N loss from the soil via leaching, ammonia volatilization, and/or denitrification. Each of these processes results in the removal of '5N depleted products from the soil and, consequently, '5N enrichment of the remaining soil. In contrast to soil results, grazers reduced plant '5N by an average of 0.7%o, probably due to isotopically light, soil N03- (compared to soil NH4+) constituting a more important N source for plants in grazed grassland relative to those in ungrazed grassland. These findings indicate that native grazers increased N loss from this north-temperate grassland as a result of accelerated losses on urine- and dung-affected microsites and, potentially, from elevated N loss throughout the grazed landscape due to grazers promoting N cycling. Furthermore, these results suggest that herbivores increase plant N03- assimi- lation, which may positively affect primary productivity in this grazed ecosystem.