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Notes: Summary Soil temperature, moisture, and CO2 were monitored at four sites along an elevation transect in the eastern Mojave Desert from January to October, 1987. Climate appeared to be the major factor controlling CO2 partial pressures, primarily through its influence of rates of biological reactions, vegetation densities, and organic matter production. With increasing elevation, and increasing actual evapotranspiration, the organic C, plant density, and the CO2 content of the soils increased. Between January and May, soil CO2 concentrations at a given site were closely related to variations in soil temperature. In July and October, temperatures had little effect on CO2, presumably due to low soil moisture levels. Up to 75% of litter placed in the field in March was lost by October whereas, for the 3 lower elevations, less than 10% of the litter placed in the field in April was lost through decomposition processes.

Notes: Abstract One-year-old red spruce seedlings were exposed to ozone at four levels (approximately 0.5, 1.0, 1.5, and 2.0 times ambient ozone concentration) and simulated acidic precipitation at three levels (pH 3.1, 4.1, and 5.1) in open-top chambers in the field during July through September, 1987. At monthly intervals, seedlings were harvested and effects of the pollutant treatments were assessed by measuring height, branch number and length, stem, needle, and root dry mass, and rate of photosynthesis. Neither pollutant caused significant effects on the variables measured, and there were no detectable interactions between the pollutants.

Notes: Abstract A linear gradient field exposure system was modified from one originally described by Shinn et al. (1977) and used to expose field grown soybeans (Glycine max cv Hark) to a concentration gradient of a mixture of two gaseous pollutants: SO2 and 03. Since this technique does not use enclosures, study plants experienced near ambient fluctuations in environmental conditions, including wind, and hence were exposed to widely fluctuating pollutant concentrations. Plants in the gradient system were exposed to both pollutants for 57 h on 12 days during the pod-filling period (31 August–17 September). Mean concentrations during the 57 h of exposure at the ‘high’ end of the gradient were 0.16 and 0.06 µl l−1 (PPM) SO2 and O3, respectively, with 10 h at greater than 0.25 and 0.10 µl−1 SO2 and O3, respectively. Total doses for these plants were estimated to be 9.0 and 3.5 µl−1 · h SO2 and O3, respectively. Comparison with plants exposed to ambient air indicated that exposure to SO2 and O3 reduced total yield per plant and dry mass per bean by as much as 36 and 15 %, respectively. Since concurrent exposure to a much higher dosage of SO2 alone (20.2 µl l−1 · h) was observed in a separate experiment to have no significant effect on yield, 03, although present at moderately low levels, was probably responsible (alone or synergistically with SO2) for the greatest reduction in seed size and yield.

Notes: Abstract Although the agents responsible for the decline of red spruce on high elevation sites in the northeast are not known, 03 and acidic rain are considered to be possible contributing stresses. The research presented in this paper constitutes the second year of a 3-yr study to evaluate and quantify the influences of 03 and acidic precipitation on seedling red spruce. Two-year old red spruce seedlings were exposed to 03 at four levels (approximately 0.5, 1.0, 1.5, and 2.0 times ambient 03 concentration) and simulated acidic precipitation at three levels (pH 3.1, 4.1, and 5.1) in open-top chambers. The exposures occurred during June through October, 1988 after the seedlings had been exposed to the pollutants the previous year. At three intervals during the exposure period, seedlings were harvested and effects of the pollutant treatments were assessed by measuring the length of the 1988 terminal shoot, the number and length of branches, the dry mass of stems, needles, and roots, and rate of photosynthesis. There were no significant effects of 03 on any of the growth variables or on photosynthesis. There was a significant effect of pH on photosynthesis; rates of photosynthesis increased as acidity of the treatment increased. However, the higher rates of photosynthesis were not reflected in increased biomass of the seedlings. Significant 03 by pH interactions occurred for several growth variables.

Notes: Abstract Substantial and widespread morbidity and mortality of red spruce have been observed in high elevation forests of the northeast under circumstances indicative of a stress-related disease. Whether red spruce at lower elevations are experiencing a more subtle loss of growth and vigor is uncertain. In addition, sugar maple has exhibited decline of varying extent and intensity for several decades. Forests in the northeast are exposed to two air pollutants, ozone (O3) and acidic precipitation, that are widespread in occurrence and have the potential, both individually and collectively, to produce impacts to forest trees. the roles, if any, of these two stress agents in the tree declines found in the northeast are not known. In 1986, a five-year study was initiated to evaluate the effects of O3 and acidic precipitation on red spruce and sugar maple. The trees will be exposed to controlled levels of O3 and acidic precipitation in the field using open-top chambers. The experiment is a 4×3 factorial conducted in split plots with O3 treatments as whole plots and simulated rain treatments comprising the split plots. Broadly stated, the research will evaluate the effects of the pollutants on the processes, fluxes, and pools associated with carbon, water, and nutrients in the soil/tree/atmosphere system. These evaluations will be conducted on a systems level and will be integrated through the development of mechanistic simulation models. Assessment of the effects of the treatments on carbon fixation by photosynthesis, the loss of carbon through respiration, and the allocation of carbon in growth will be a central focus of the study. Whole-tree cuvettes will be used to assess net photosynthesis, respiration, transpiration, and stomatal conductance. Considerable emphasis will be placed on determining the influences of the treatments on the biogeochemistry of the system. These studies will focus on the leaching of nutrients from the tree canopy, the mobilization and loss of nutrients from the soil, soil solution chemistry, and the alteration of tree nutrition by the input of additional nitrogen in precipitation. Statistical and simulation modeling will be used to assess and describe the effects of the treatments. The modeling approaches are different in technique, but complementary. Statistical models will be used to describe the responses of growth and physiological variables to the ozone and acidic precipitation treatments. Simulation models will be built to describe the relationships between photosynthesis, respiration, nutrition, and water use, how these processes are affected by the treatments, and how these effects ultimately result in altered growth. The simulation models will initially provide a framework for the formulation of hypotheses regarding the interrelationships of plant components and processes and how they are affected by the treatments.

Notes: Abstract Net photosynthesis (Phn), leaf resistance, and transpiration of a naturally occurring hybrid of Pinus contorta Loud. and P. banksiana Lamb. (lodgepole pine × jack pine) were measured as part of a case study investigating the chronic exposure of a forest ecosystem to low concentration S gas emissions from a S recovery gas plant in west central Alberta, Canada during 1975 and 1976. The objectives of this portion of the case study were to determine if chronic low concentration exposure to S gas emissions had produced any accumulative effect on the Phn of the pine trees and to determine if ambient SO2 concentrations had any immediate effect on Phn. Sulphur dioxide concentrations above 0.01 ppm occurred on 87% and 71 % of the monitoring days at the intensive experimental site during 1975 and 1976, respectively. The maximum half-hour daylight concentrations of SO2 were 0.21 ppm and 0.12 ppm in 1975 and 1976, respectively. Photosynthetic performance was not affected by controlled SO2 exposures in the laboratory below 0.23 ppm for 30 min, but it was always depressed by exposure to SO2 above 0.25 ppm for 30 min. Ambient concentrations of SO2 in the field had no measurable immediate effect on Phn. However, the seasonal mean rates of Phn of current year (1976) and 1-yr old (1975) pine foliage were significantly lower at the frequently exposed sites than the infrequently exposed site (3.9 and 3.4 mg CO2 g dw−1 h−1 versus 6.4 and 5.1 mg CO2 g dw−1 h−1, respectively). The current year's foliage sampled at the sites infrequently exposed to S gases achieved positive rates of net CO2 exchange one to three weeks earlier than foliage from the three frequently exposed sites. Foliar sulphate-S concentrations, however, were only poorly correlated with Phn rates. The reduced rates of net photosynthesis and shorter period of positive net CO2 exchange in current year's foliage frequently exposed to S gas emissions combined with the shorter needle retention time and foliar chlorosis may partly explain the previously reported lowered productivity of these trees as measured by basal area increment.

Notes: Abstract 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.

Notes: Abstract 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.

Notes: Abstract 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.