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Notes: Abstract An acidic precipitation delivery system is described that was designed and constructed for use in a field investigation of the response of red spruce saplings (Picea rubens Sarg.) to the interactive stresses of ozone and acid rain. The system utilizes hydraulic, solid-cone spray nozzles to produce simulated rainfall with droplet size distributions approximating natural rain events, which are of low intensity, i.e., about 1–1.5 cm hr−1, and are relatively uniform in distribution of volume over a 2.4 m diameter plot. Three different pH treatments (3.1, 4.1, 5.1) were dispensed randomly to each of three treatment subplots located in twelve open-top field chambers and three ambient control chambers. Storage capacity of the system permitted a 2.3 hr rain event. Construction materials used were chosen for resistance to the corrosive nature of the rain simulant, stability to ambient UV radiation, and resistance to penetration by sunlight. Simulated events were not synchronized to ambient events, but were scheduled to prevent moisture deficits.

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 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 An exposure system for exposing plants to gradients of gaseous air pollutants in the field was tested using sulfur dioxide SO2 and hydrogen fluoride (HF). Well defined linear gradients of SO2 concentration and HF flux were easily produced and were repeatable from exposure to exposure. The gradients were altered by wind speed and direction, but in tightly closed canopies, the alterations were minor. This system has many advantages: a graded series of exposures can be conducted in a small area, plants may be grown using accepted cultural practices, the cost of the apparatus is low, and more than one pollutant can be used, either concurrently or countercurrently. Disadvantages include the requirement for an intensive air monitoring network and an unnatural vertical pollutant profile in the canopy. The gradient system should be used as a supplement to open-top chambers, and not as a replacement for them.

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.