J.A. Laurence

A comparison of indices that describe the relationship between exposure to ozone and reduction in the yield of agricultural crops

Abstract The objective of this study is to compare the use of several indices of exposure in describing the relationship between O 3 and reduction in agricultural crop yield. No attempt has been made to determine which exposure-response models best fit the data sets examined. Hourly mean O 3 concentration data, based on two-three measurements per hour, were used to develop indices of exposure from soybean and winter wheat experiments conducted in open-top chambers at the Boyce Thompson Institute, Ithaca, New York NCLAN field site. The comparative efficacy of cumulative indices (i.e. number of occurrences equal to or above specific hourly mean concentrations, sum of all hourly mean concentrations equal to or above a selected level, and the weighted sum of all hourly mean concentrations) and means calculated over an experimental period to describe the relationship between exposure to O 3 and reductions in the yield of agricultural crops was evaluated. None of the exposure indices consistently provided a best fit with the Weibull and linear models tested. The selection of the model appears to be important in determining the indices that best describe the relationship between exposure and response. The focus of selecting a model should be on fitting the data points as well as on adequately describing biological responses. The investigator should be careful to couple the model with data points derived from indices relevant to the length of exposure. While we have used a small number of data sets, our analysis indicates that exposure indices that weight peak concentrations differently than lower concentrations of an exposure regime can be used in the development of exposure-response functions. Because such indices may have merit from a regulatory perspective, we recommend that additional data sets be used in further analyses to explore the biological rationale for various indices of exposure and their use in exposure-response functions.

Chronic ozone exposure alters the growth of leaves, stems and roots of hybrid Populus

Rooted cuttings of hybrid Populus (DN34, Populus deltoides x nigra) were grown outdoors in pots in open-top chambers at Ithaca, NY (74.5 degrees W, 42.5 degrees N), during 1988 and 1989 (experiment 1) and during 1989 and 1990 (experiment 2). Ambient air was passed through charcoal filters to produce a 0.5 times ambient ozone treatment, and ozone generated from oxygen was added to produce one and two times ambient ozone treatments. In experiment 1, treatments were applied for 8-12 h each day for 112 days of the 1988 growing season, then the plants were grown outdoors with ambient ozone in 1989. In experiment 2, treatments were applied for 9 h each day for 98 days of the 1989 growing season, then the plants were grown outdoors with ambient ozone in 1990. Chronic exposure to ozone caused the following changes (statistically significant in one or both experiments at p<0.05): (1) earlier leaf abscission, (2) decreased stem basal diameter, (3) decreased stem mass, (4) decreased internode length, (5) decreased shoot height p=0.005, and (6) decreased leaf size in the growing season following ozone treatment. There was also strong evidence that ozone increased the number of leaves produced p=0.055. Finally, there was some evidence that ozone increased the ratio of shoot mass to root mass p=0.093.

Response of red spruce seedlings exposed to ozone and simulated acidic precipitation in the field

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.

Egyptian plant species as new ozone indicators.

The aim of this study was to test and select one or more highly sensitive, specific and environmentally successful Egyptian bioindicator plants for ozone (O3). For that purpose more than 30 Egyptian species and cultivars were subjected to extensive screening studies under controlled environmental and pollutant exposure conditions to mimic the Egyptian environmental conditions and O3 levels in urban and rural sites. Four plant species were found to be more sensitive to O3 than the universally used O3-bioindicator, tobacco Bel W3, under the Egyptian environmental conditions used. These plant species, jute (Corchorus olitorius c.v. local), clover (Trifolium alexandrinum L. c.v. Masry), garden rocket (Eruca sativa c.v. local) and alfalfa (Medicago sativa L. c.v. local), ranked in order of decreasing sensitivity, exhibited typical O3 injury symptoms faster and at lower 03 concentrations than Bel W3. Three variables were tested in search of a reliable tool for the diagnosis and prediction of O3 response prior to the appearance of visible foliar symptoms: pigment degradation, stomatal conductance (g(s)) and net photosynthetic CO2 assimilation (Pnet). Pigment degradation was found to be unreliable in predicting species sensitivity to O3. Evidence supporting stomatal conductance involvement in 03 tolerance was found only in tolerant species. A good correlation was found between g(s), restriction of O3 and CO2 influx into the mesophyll tissues, and Pnet. Changes in Pnet seemed to depend largely on fluctuations in g(s).

Effects of ozone and acidic precipitation on the growth and photosynthesis of red spruce after two years of exposure

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.

Evaluation of growth and yield of soybean exposed to ozone in the field

Abstract Soybeans ( Glycine max (L.) Merr. cv Hodgson) were exposed in the field to seasonal 7-h average concentrations of 0·017, 0·035, 0·060, 0·084 and 0·122 μl litre −1 ozone using open-top chambers and ambient plots. Dose-response studies were conducted on growth and yield. Negative linear relationships were found between both growth and yield and ozone exposure. The regression equation: yield= 12·82 − (48·17 × O 3 ), with yield in grams per plant and O 3 as the seasonal 7-h average, expresses one relationship. Compared with the yield in charcoal filtered air (0·017 μl litre −1 ), losses ranged from 8% in the 0·035 μl litre −1 treatment to 41% in the 0·122 μl litre −1 treatment. Aboveground biomass was a good indicator of ozone stress; five weeks after the ozone treatments were initiated, a negative linear relationship was found between ozone exposure and aboveground biomass. In contrast, the percentage of biomass allocated to leaves, stems and pods did not change until after 6 to 7 weeks of exposure to ozone. The change in allocation of biomass was the result of accelerated senescence of older leaves. At final harvest, a lower percentage of aboveground biomass was found in pods and seeds of plants exposed to higher ozone concentrations.

Assessing potential climate change effects on loblolly pine growth: A probabilistic regional modeling approach

Abstract Most models of the potential effects of climate change on forest growth have produced deterministic predictions. However, there are large uncertainties in data on regional forest condition, estimates of future climate, and quantitative relationships between environmental conditions and forest growth rate. We constructed a new model to analyze these uncertainties along with available experimental results to make probabilistic estimates of climate change effects on the growth of loblolly pine ( Pinus taeda L.) throughout its range in the USA. Complete regional data sets were created by means of spatial interpolation, and uncertainties in these data were estimated. A geographic information system (GIS) was created to integrate current and predicted climate data with regional data including forest distribution, growth rate, and stand characteristics derived from USDA Forest Service data. A probabilistic climate change scenario was derived from the results of four different general circulation models (GCM). Probabilistic estimates of forest growth were produced by linking the GIS to a Latin Hypercube carbon (C) budget model of forest growth. The model estimated a greater than 50% chance of a decrease in loblolly pine growth throughout most of its range. The model also estimated a 10% chance that the total regional basal area growth will decrease by more than 24×10 6 m 2 yr −1 (a 92% decrease), and a 10% chance that basal area growth will increase by more than 62×10 6 m 2 yr −1 (a 142% increase above current rates). The most influential factor at all locations was the relative change in C assimilation. Of climatic factors, CO 2 concentration was found to be the most influential factor at all locations. Substantial regional variation in estimated growth was observed, and probably was due primarily to variation in historical growth rates and to the importance of historical growth in the model structure.

Yield response of red kidney bean Phaseolus vulgaris ti incremental ozone concentrations in the field

Abstract Field-grown red kidney beans were exposed to incremental levels of ozone in open-top chambers for 21 days during pod filling. Treatments consisted of ambient plots without chambers, chambers receiving charcoal-filtered air and chambers receiving non-filtered air to which either 0·00, 0·03, 0·06 or 0·09 ppm O 3 was added for 7 h each day. The addition of 0·06 or 0·09 ppm O 3 produced foliar injury, extensive defoliation and reductions in per plant bean yield of 24 and 27%, respectively. Regression analysis indicated a significant linear relationship between the 7-h mean O 3 concentration and yield per plant. This relationship was expressed as: Yield = 17·44 – 35·51 (CONC).

Moderate water stress alters carbohydrate content and cold tolerance of red spruce foliage

Abstract Red spruce ( Picea rubens Sarg.) has been tested for response to many environmental stresses and found to be relatively tolerant. An explanation for this tolerance is its maintenance of high levels of carbohydrate reserves, mainly soluble sugars and starch, which change with alterations in photosynthetic capacity, rate of growth and degree of cold tolerance through the year. Red spruce saplings responded to moderate water stress in early September by depleting foliar starch and maintaining foliar soluble sugars. Foliar carbohydrate contents of water-stressed trees were restored to control levels within 1 week of rewatering. During and immediately after the water-stress period, foliage of water-stressed trees was more cold tolerant than foliage of well-watered trees as measured by relative electrolyte leakage. Two months after termination of the water-stress treatment, starch content of fine roots and cold tolerance of foliage of well-watered trees were significantly higher than those of water-stressed trees. Before the trees became fully cold tolerant, differences between treatments in the degree of foliar cold tolerance were positively associated with differences in soluble sugar content. As trees became more cold tolerant, soluble sugar contents were not related to the degree of cold tolerance. These results suggest that species with substantial reserves withstand periods of reduced carbon fixation by utilizing reserves for maintenance; however, lowered reserves could result in increased susceptibility to subsequent stresses.

Field tests of a linear gradient system for exposure of row crops to S02 and HF

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.