Preferential denervation of the adductor muscles of the equine larynx. I: Muscle pathology

The laryngeal muscles of 18 horses were examined histologically. The neurogenic changes found in each muscle were scored by four reviewers and the results evaluated statistically. Fifteen of these horses had endoscopic evidence of abnormal laryngeal function, three of which were defined as having adductor paralysis. Measurement of muscle fibre area in two horses with idiopathic laryngeal hemiplegia (ILH) was performed. In the quantitative study of neurogenic change, the adductor muscles were more significantly affected than the abductor muscle. This was also true in the clinical cases of ILH where measurement of muscle fibre area demonstrated that the lateral cricoarytenoid (adductor) muscles showed a wider range of pathological changes than the dorsal cricoarytenoid muscle (abductor). Those horses with the most severe muscle pathology also had the most abnormal endoscopic findings. The propensity for denervation of the adductor muscles should provide clues as to the pathogenesis and natural history of horses with sub-clinical laryngeal disease and ILH.     

Influence of foliar N on foliar soluble sugars and starch of red spruce saplings exposed to ambient and elevated ozone

Red spruce (Picea rubens Sarg.) trees growing at high elevation in the northeastern United States have experienced decline in recent years but seedlings have proved to be relatively tolerant of a wide range of environmental stresses in controlled studies. One possible reason for the wide tolerance to stress in seedlings is their inherently large pool of carbohydrate reserves, which is available for maintenance during and regrowth after periods of stress. We tested for the effects of foliar N and exposure to ozone on foliar carbohydrate reserves of 20-year-old naturally regenerated saplings. The trees were maintained in native soil in 360-l containers for 5 years before the experiment. The year before the experiment, trees were fertilized with N,P,K to provide a population of trees from N deficient to N sufficient. As foliar N decreased below 0.9%, length of current-year shoots and specific needle area of current-year needles declined. Foliar N concentration was correlated with foliar sugar and starch concentrations, but relationships varied with time of year. Before bud break, foliar carbohydrates and N, in general, were positively correlated, and date of bud break was delayed in N-deficient trees. During active growth, foliar soluble sugars and N were positively correlated, but starch concentrations were negatively correlated with N. By late September, neither starch nor sugar concentration was correlated with N concentration. Ozone and foliar N concentrations did not interact to change foliar carbohydrate concentrations or shoot and needle growth in this relatively short-term study.     

Boxelder water sources and physiology at perennial and ephemeral stream sites in Arizona

To assess the influence of stream water on leaf gas exchange and water potential in different sized boxelder trees (Acer negundo L.), we compared these characteristics in trees growing beside a perennial stream and a nearby ephemeral stream in a montane-riparian forest in northern Arizona. Patterns of tree water use were quantified by stable isotope analysis (delta(18)O). Physiological characteristics were similar for large and small trees. Similarity between sites in predawn and daytime water potentials and xylem delta(18)O indicated that stream water was not a physiologically important water source. Seasonal and site variations in light-saturated net photosynthetic rate were significantly related to leaf-to-air vapor pressure deficit (r = -0.691) and foliar nitrogen concentration (r = 0.388). Although deep water was the dominant water source, surface soil water was utilized following precipitation, especially by small trees. We conclude that net carbon gain and severity of water stress are only weakly coupled to stream water availability.     

Ambient levels of ozone reduce net photosynthesis in tree and crop species

Experiments were conducted to measure the photosynthetic response of three crop and four tree species to realistic concentrations of ozone and (for tree species only) simulated acidic rain. The ozone concentrations were representative of those found in clean ambient air, in mildly to moderately polluted air such as occurs in much of the United States during the summer, and in more heavily polluted air. However, the highest concentrations of ozone used were lower than those found regularly in the Los Angeles area. The mean pH of the simulated acid rain treatments ranged from more alkaline to much more acidic than the mean pH of precipitation in the United States. Exposure to any increase in ozone reduced net photosynthesis in all species tested. In contrast, acidic rain had no negative effect on photosynthesis in tree species, and no interaction between ozone and acidic rain was observed. Ozone-induced reductions in photosynthesis were related to declines in growth or yield. Species with higher stomatal conductances and thus higher potential for pollutant uptake exhibited greater negative responses to similar ozone treatments. Since exposure to ozone concentrations typical of levels of the pollutant observed in the eastern half of the United States reduced the rates of net photosynthesis of all species tested, reductions in net photosynthesis may be occurring over much of the eastern United States.     

Sulphur gas emissions in the boreal forest: The West Whitecourt case study VIII: Pine tree mineral nutrition

Nutrient analyses of foliage from a naturally occurring hybrid of Pinus contorta Loud. and P. banksiana Lamb. (lodgepole pine × jack pine), were used to determine if chronic exposure to S gas emissions had affected the nutrient status of the trees. This study was part of a larger case study investigating the effects of 17 yr of exposure to S gas emissions from a S-recovery gas plant on a forest ecosystem in west central Alberta, Canada. Significant inverse, linear relationships were found between foliar sulphate-S levels and distance from the S source in all three age classes of pine foliage tested. Sulphate-S levels increased with increasing age of foliage at sites near the source while they decreased with increasing age of foliage at sites not frequently exposed to the S gas emissions. Soil pH was reduced in the top 5 cm of soil at sites near the source and elevated contents of total S in the soil were also found at those sites. Manganese concentrations in foliage from the sites near the source were significantly higher than in foliage from sites away from the source. The level of Mn also increased with increasing age of tissues. The elevated level of sulphate-S in foliage and lower soil pH at sites near the source indicated significant amounts of S from the source had been deposited at those sites. The lower soil pH most likely contributed to the increased availability of Mn that was found in the foliage.     

Mineralogical control of organic carbon dynamics in a volcanic ash soil on La Réunion

In soil carbon dynamics, the role of physicochemical interactions between organic matter and minerals is not well understood nor quantified. This paper examines the interactions between soil organic matter and poorly crystalline aluminosilicates in a volcanic ash soil on La Réunion in the southern tropics. The soil examined is a profile composed of a surface soil (L-Ao-E-Bh) overlying four buried horizons (horizons 2Bw, 3Bw, 4Bw, 5Bw) that have all developed from successive tephra deposits. Non-destructive spectroscopy (XRD, FTIR and NMR of Si and Al) showed that the mineralogical composition varies from one buried horizon to another. Further, we show that buried horizons characterized by large amounts of crystalline minerals (feldspars, gibbsite) have the least capacity to store organic matter and the fastest carbon turnover. In contrast, buried horizons containing much poorly crystalline material (proto-imogolite and proto-imogolite allophane, denoted LP-ITM) store large amounts of organic matter which turns over very slowly. To understand the mechanism of interactions between LP-ITM and organic matter better, we focused on a horizon formed exclusively of LP-ITM. We demonstrate, using Δ¹⁴C and δ¹³C values, that even though LP-ITM is extraordinarily effective at stabilizing organic matter, C linked to LP-ITM is still in dynamic equilibrium with its environment and cycles slowly. Based on Δ¹⁴C values, we estimated the residence time of organic C as ∼ 163 000 years for the most stabilized subhorizon, a value that is comparable to that for organic carbon stabilized in Hawaiian volcanic soils. However, this calculation is likely to be biased by the presence of microcharcoal. We characterized the organo-mineral binding between organic matter and LP-ITM by ²⁷Al NMR, and found that the organic matter is not only chelated to LP-ITM, but it may also limit the polymerization of mineral phases to a stage between proto-imogolite and proto-imogolite allophane. Our results demonstrate the important role of poorly crystalline minerals in the storage of organic C, and show that mineral and organic compounds have to be studied simultaneously to understand the dynamics of organic C in the soil.     

Environmental effects on pregnancy rate in beef cattle

Ten years of calving records were examined from Bos taurus crossbred cows (mean of 182 cows/yr) to quantify the effects of environmental conditions during the breeding season on pregnancy rate. Estimated breeding dates were determined by subtracting 283 d from the calving date. Relationships were determined between the proportion of cows bred during the periods from the beginning of the breeding season until d 21, 42, and 60 of the breeding season and the corresponding environmental variables. Weather data were compiled from a weather station located approximately 20 km from the research site. Average daily temperature and relative humidity were used to calculate daily temperature-humidity index (THI). Daily averages for each environmental variable were averaged for each period. Minimum temperature (MNTP) and THI for the first 21 and 42 d of the breeding season were negatively associated (P < 0.001) with pregnancy rate. For the 0-to 21-d, 0- to 42-d, and 0- to 60-d breeding periods, respective r2 for average temperatures were 0.32, 0.37, and 0.11, whereas r2 for MNTP were 0.45, 0.40, and 0.10 and r2 for THI were 0.38, 0.41, and 0.11, respectively, for the same breeding periods. The negative associations of temperature and THI with pregnancy rate are most pronounced during the first 21 d of the breeding season, with a -3.79 and -2.06% change in pregnancy rate for each unit of change in MNTP and THI, respectively. A combination of environmental variables increased the R2 to 0.67. In this analysis, windspeed was found to be positively associated with pregnancy rate in all equations and increased the R2 in all breeding periods. Optimum MNTP for the 0- to 21-d, 0- to 42-d, and 0- to 60-d breeding periods was 12.6, 13.5, and 14.9 degrees C, respectively. For the 0- to 60-d breeding period, optimum THI was 68.0, whereas the THI threshold, the calculated level at which cattle will adapt, was found to be 72.9. Reductions in pregnancy rate are likely when the average MNTP and THI equal or exceed 16.7 degrees C and 72.9, respectively, and for Bos taurus beef cows that are pasture bred during a 60-d spring-summer period.     

Measurement of Resting and Stress-elevated Serum Cortisol in Rainbow Trout Oncorhynchus mykiss in Experimental Net-pens

A commercially available heterogeneous, solid-phase tube enzyme-linked immunoassay (ELISA) was modified and validated for the measurement of serum cortisol in rainbow trout Oncorhynchus mykiss . The assay is accurate and precise. Resting and stress-elevated serum cortisol concentrations were measured in rainbow trout with a sensitivity of 1.5 ng/ml. Fish held in net-pens at a density of 0.4 kg/m³/cm had a resting cortisol level of 16.5 ± 3.8 ng/ml (mean ± SE). At 3 h postdisturbance, serum cortisol levels were not affected by the removal of fish from adjacent net-pens with dip nets or by the use of 200 mg/L tricaine methanesulfonate (MS-222) as an anesthetic for obtaining samples. However, an acute stress (60 s removal from water) elevated serum cortisol levels to 73.7 ± 9.4 ng/ml.     

Field studies of pine,spruce and aspen periodically subjected to sulfur gas emissions

Field studies of photosynthesis in Pinus contorta/Pinus banksiana (lodgepole pine/jack pine) hybrids, Picea glauca (white spruce) and Populus tremuloides (aspen) subjected to SO₂ and H₂S from a nearby natural gas processing plant were initiated near Whitecourt, Alberta, Canada during the summer of 1974. The site was characterized as a Pinus-Picea glauca/Arctostaphylos uva-ursi association (pine-white spruce/bearberry). A 15 m high scaffold was used as access to mid-crown foliage in the pines while the spruce and aspen were accessible from the round. Net assimilation rates, transpiration rates and leaf resistances were calculated and water deficits were monitored. Photosynthetic rates measured were in a low range for the conifers studied, with pine having a maximum of 3.28 mg dm^?2 h^?1 and white spruce a maximum value of 2.3 mg dm^?2 h^?1 The low maximum photosynthetic rate determined for aspen is thought to be attributable to the onset of autumn. Chemical analyses for SO₄-sulfur using the methylene blue colorimetric method of Johnson and Nishita (1952) showed levels of 300 to 700 ppm, with the older foliage showing slightly higher values. Visible chronic S02 symptoms had a pronounced sun, or upward, orientation. Ambient SOD H₂S and total S were measured using a Tracor 270HA Atmospheric Sulfur Analyzer (chromatographic method) and trends in ambient SO₂ concentrations using an Envirometrics SO₂ Analyzer (polarographic method). Concentration was found to be variable for SO₂ and generally below 0.05 ppm. A concentration gradient of SO₂ was found to exist in the lodgepole pine/jack pine stand with the SO₂ values above the canopy generally higher than below the canopy (0.1 ppm above and 0.05 ppm below). This condition was occasionally reversed. The plant canopy is considered to act as a barrier to downward diffusion of the S emissions in the first case and also a barrier to upward diffusion of S emissions present due to advection in the stand in the second case. The vegetative environment surrounding the Windfall Gas Plant is definitely affected by S gas emissions but the extent remains to be determined.     

Fluoride deposition via litterfall in a coastal-plain pine plantation in South Carolina

The concentration of fluoride in needles, its effects on tree defoliation and on decomposition of needles (litter), and its subsequent accumulation in the upper soil horizons were observed in pine plantations near and far from a new aluminum smelter. Pinus taeda and Pinus palustris stands within 0.8 km of the smelter had significantly higher levels of foliar F than a P. taeda stand 1.8 km from the source. Neither temporal patterns nor amounts of needlefall were altered by airborne F from the smelter. In addition, elevated levels of foliar F did not affect the rate of decomposition of pine needles over a period of 6 mo. Soluble F in soil samples increased significantly in the upper 10 cm of the soils at the sites nearest the F source over a period of 7 yr since the start of F emissions.