Clinical monitoring of neuromuscular function.

With the advent of shorter-acting non-depolarizing neuromuscular blocking drugs, the use of nerve stimulation as a means of monitoring the neuromuscular junction has become more widespread. This article describes the patterns of nerve stimulation and modes of monitoring muscular response in current clinical use. These patterns and modes are compared and their clinical relevance is discussed.

Contributions of Autotrophic and Heterotrophic Nitrifiers to Soil NO and N(2)O Emissions.

Soil emission of gaseous N oxides during nitrification of ammonium represents loss of an available plant nutrient and has an important impact on the chemistry of the atmosphere. We used selective inhibitors and a glucose amendment in a factorial design to determine the relative contributions of autotrophic ammonium oxidizers, autotrophic nitrite oxidizers, and heterotrophic nitrifiers to nitric oxide (NO) and nitrous oxide (N(2)O) emissions from aerobically incubated soil following the addition of 160 mg of N as ammonium sulfate kg. Without added C, peak NO emissions of 4 mug of N kg h were increased to 15 mug of N kg h by the addition of sodium chlorate, a nitrite oxidation inhibitor, but were reduced to 0.01 mug of N kg h in the presence of nitrapyrin [2-chloro-6-(trichloromethyl)-pyridine], an inhibitor of autotrophic ammonium oxidation. Carbon-amended soils had somewhat higher NO emission rates from these three treatments (6, 18, and 0.1 mug of N kg h after treatment with glucose, sodium chlorate, or nitrapyrin, respectively) until the glucose was exhausted but lower rates during the remainder of the incubation. Nitrous oxide emission levels exhibited trends similar to those observed for NO but were about 20 times lower. Periodic soil chemical analyses showed no increase in the nitrate concentration of soil treated with sodium chlorate until after the period of peak NO and N(2)O emissions; the nitrate concentration of soil treated with nitrapyrin remained unchanged throughout the incubation. These results suggest that chemoautotrophic ammonium-oxidizing bacteria are the predominant source of NO and N(2)O produced during nitrification in soil.

Nitrous oxide emissions from an irrigated cornfield.

During the 1978 growing season, nitrous oxide (N(2)O) emissions from a typical well-managed northern Colorado field of corn (Zea mays L.) totaled approximately 2.6 kilograms of nitrogen per hectare, or about 1.3 percent of the applied fertilizer nitrogen. Thirty percent of the loss occurred during the 3 weeks following fertilization while ammonia was being rapidly nitrified, and 59 percent was emitted during the week after the field's first irrigation, when restricted oxygen diffusion favored denitrification. Considering the large spatial and temporal variability of N(2)O emissions from soil, micrometeorological estimates of vertical N(2)O flux density compared favorably with estimates based on a simple soil cover method.

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.

Atmospheric ammonia: absorption by plant leaves.

By monitoring the disappearance of ammonia from an airstream flowing through a small growth chamber containing a single plant seedling, it was discovered that plant leaves absorb significant quantities of ammonia from the air, even at naturally occurring low atmospheric concentrations. The measured absorption rates of ammonia showed large diurnal fluctuations and varied somewhat among species, but differed little with the nitrogen fertility level of plants within a species.

Nitrogen enrichment of surface water by absorption of ammonia volatilized from cattle feedlots.

Apparatus designed to measure absorption of ammonia from the air by aqueous surfaces was installed near several cattle feedlots and in appropriate control areas. Ammonia absorption rates measured near feedlots were as much as 20 times greater than near the control. Their magnitudes indicate that absorption of ammonia volatilized from cattle feedlots contributes significantly to the nitrogen enrichment of surface water in the vicinity of feedlots.