Air containing nitrogen-15 ammonia: foliar absorption by corn seedlings

Thirty-day-old corn seedlings, grown in the greenhouse with different concentrations of supplemental nitrate nitrogen, were moved to a constant-temperature growth chamber and sealed in a 560-liter tent made of polyvinyl chloride. The plants were exposed to air containing ammonia labeled with nitrogen-15 (1, 10, and 20 parts per million) for 24 hours and then harvested. The nitrogen-15 content of the tops and roots showed that at 1 part per million 43 percent of the ammonia was absorbed, whereas at 10 and 20 parts per million, 30 percent of the ammonia was absorbed. The results demonstrate that growing plants may be a natural sink for atmospheric ammonia.     

Effect of ensiled hop (Humulus lupulus L.) residues on plasma acetate turnover rate in sheep

An isotope dilution method using [1‐¹³C]sodium acetate was applied to determine the effect of feeding ensiled hop (Humulus lupulus L.) residues on plasma acetate turnover rate in six adult crossbred sheep. The sheep were fed 63 g/kg body weight (BW)^0.75/day of either mixed hay of orchardgrass (Dactylis glomerata L.) and reed canarygrass (Phalaris arundinacea L.) and round bale silage at 3:1 ratio (Hay‐diet), or another where round bale silage was replaced by ensiled hop residues (Hop‐diet) with a crossover design each of a 3‐week period. The isotope dilution method was performed on day 21 of each dietary treatment. Dry matter digestibility was similar between diets, and nitrogen (N) digestibility was lower (P = 0.001) for Hop‐diet than Hay‐diet. However, N retention did not differ between diets. Plasma acetate concentration was lower (P = 0.04) for Hop‐diet than Hay‐diet, and the turnover rate of plasma acetate did not differ between diets. Plasma concentration of lactate and non‐esterified fatty acids were similar between diets. Hop‐diet was found almost comparable to Hay‐diet on plasma acetate turnover rate in the present experimental conditions. Therefore, it could be concluded that hop residues partially could be used as an alternative to traditionally used round bale silage for rearing sheep.     

Recovery of previously acidified lakes near Coniston,Canada following reductions in atmospheric sulphur and metal emissions

The purpose of the present study was to assess the rate of recovery of acidified lakes located near the town of Coniston following an abrupt reduction in atmospheric SO₂ and metal emissions at the Coniston smelter which closed in 1972. The water chemistry of several lakes was studied over a period of 16 yr (1968–1984). In one extremely acidic lake close to the smelter, the pH increased from 4.05 in 1972 to 5.8 in 1984. Conductivity, as well as concentrations of SO₄, Cu, Ni, Co, Mn, and Zn decreased by 60% to 90% in the lake water during the same period. In another initially less acidic lake nearby, the increase in pH was less dramatic, while the decrease in conductivity, SO₄, and some metals was similar to that of the more acidic lake. Local SO₄ deposition decreased approximately 75 % while Cu and Ni deposition decreased by 90% following closure of the Coniston smelter. These results indicate that even severely acidified lakes can improve within a few years following a substantial reduction in atmospheric S emissions; and that in some regions recovery can occur due to reductions in SO₂ emissions even in the absence of concurrent NO_x control.     

The dispersal of Culicoides brevitarsis in eastern New South Wales and associations with the occurrences of arbovirus infections in cattle

Distributions of the vector Culicoides brevitarsis Kieffer (Diptera: Ceratopogonidae) (determined from light trap data) and 2 arboviruses (determined from seroconversions in sentinel cattle) were studied in eastern New South Wales in 1993–94. C brevitarsis was recorded progressively from endemic areas on the north coast, to Nowra on the south coast, and westward to Scone, in the Hunter Valley. C brevitarsis also survived through winter at Paterson, in the Hunter Valley. Its apparently focal reappearance in this marginal area had no obvious effect on the broad pattern of its progression or the dispersal of Akabane and bluetongue viruses. These viruses were first recorded from foci near Coffs Harbour, on the mid-north coast. Their first occurrences at different locations were associated with those of C brevitarsis, but not with each other. The viruses were found only within the recorded limits of the vector's distribution. Delays between the initial occurrence of C brevitarsis and first evidence of virus transmissions at locations ranged from 2 to 7 months. The delays decreased away from the points of focus and were negatively associated with the time of initial occurrence of the vector. Seroconversions to the viruses were related to the presence of C brevitarsis. However, the densities of C brevitarsis had no apparent effect on the initial numbers of cattle seroconverting to either virus. The results support the conclusion that the progressions of C brevitarsis and Akabane and bluetongue viruses were the result of gradual movements by the vector.