R.J. Kohut

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.

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.

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.

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).

The long-term effects of carbon dioxide on natural systems: issues and research needs

Research on the responses of plants to increasing levels of carbon dioxide has largely assessed physiological, phenotypic, and community-level effects. Little attention has been directed to investigating the possibility that escalating levels of carbon dioxide may serve as a selection pressure altering the genetic diversity of plant populations. Plant populations exposed to elevated levels of heavy metals or ozone have been shown to undergo selection, and it is reasonable to consider that populations experiencing long-term exposure to escalating levels of carbon dioxide may show similar responses. Selection of this nature could be particularly significant because of the global extent of the effect. Genetic selection occurs when plants are subject to an agent of selection and three conditions for a property responsive to the agent are satisfied at the population level. In the population, variation must exist in the property, part of the variation must be genetically controlled, and variation in the property must affect reproductive fitness. If these conditions are satisfied, the frequency distribution of the property, and the gene frequency associated with it, will change over time in response to the agent of selection. Research on the selection pressure effects of carbon dioxide involves assessments that integrate across temporal, spatial, and biological scales, and embrace variation in the environment and genetics. To be effective, the research will have to adopt approaches that have not been commonly employed in previous air quality studies. The questions posed are biologically complex, and new research approaches and methods are required to answer them. Some of the new approaches that can be used to assess changes in gene frequency include use of natural carbon dioxide gradients, model plant systems, molecular markers, and DNA microarray technology.

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.

Response of sugar maple to multiple year exposures to ozone and simulated acidic precipitation

Potted sugar maple seedlings were exposed to ozone and acidic precipitation in open-top chambers for three consecutive growing seasons. Periodic measurements of photosynthesis, dark respiration, through-fall and soil solution chemistry, and annual measurements of the weight of plant parts were made. Experimental treatments caused few and minor effects on above- or below-ground growth of the seedlings, even after three growing seasons. There were trends for reduced photosynthesis in trees exposed to elevated concentrations of ozone and increased photosynthesis in those exposed to the lowest pH simulated rain treatment. The chemistries of soil-solutions and through-fall were not altered significantly by treatment. Although major effects were not observed, sugar maple may respond to exposures that take place over a significant part of its life cycle.

Physiological response to controlled freezing of attached red spruce branches

Abstract Previous studies of foliar cold tolerance in red spruce ( Picea rubens Sarg.) have been conducted on isolated shoots or needles. These studies therefore could not show either the type or amount of visible injury to attached foliage in a natural environment after controlled freezing stress, or the physiological response, if any, of visibly undamaged foliage. It was hypothesized that even when visible injury did not develop, foliage on frozen, attached branches would show long-term alterations in electrolyte leakage, water balance, and gas exchange capacity as a result of severe freezing stress. In mid-December 1990, intact, attached branches of red spruce saplings which had been exposed to controlled ozone levels (1 × or 2 × ambient) and precipitation acidity (pH 3.1 or 5.1) were frozen to −48 or −54°C. Neither ozone nor precipitation acidity affected any measure of freezing injury at P ⩽ 0.1. During the 3 months following freezing, current-year shoots developed either a brown needle discoloration, needle abscission without visible discoloration, or no obvious needle discoloration or abscission. This is the first experiment to show that severe freezing stress can lead to abscission of visibly undamaged needles from an attached branch. All frozen current-year needles had elevated relative electrolyte loss ( REL ) with 24 hr after freezing, but REL subsequently declined for needles without visible discoloration. One day after freezing, average relative water content ( RWC ) of needles on frozen and unfrozen shoots was about 85%, and RWC remained above 80% throughout the winter for unfrozen shoots. By mid-January, needle RWC on visibly injured shoots averaged about 50%. RWC of experimentally frozen needles without visible injury feel more slowly to between 65 and 76% by late February. Across all shoot types, REL just after freezing was negatively correlated with needle RWC 1 month later, and also with maximum dark respiration ( R ), conductance to water vapor ( g ), and light-saturated net photosynthesis ( A ) measured on detached shoots at 12–20°C in late January to February. In unfrozen shoots, net photosynthesis reached a maximum of about 5 μmol m −2 s −1 . Shoots with visible needle injury and shoots from branches which later showed needle abs cission had very large reductions in mean maximum gas exchange (> 50% for R , > 60% for g , and > 90% for A ) compared to unfrozen shoots. On frozen branches which retained needles, non-visibly injured shoots had declining dark respiration rates and reductions of about 40% in maximum conductance and net photosynthesis, suggesting physiological damage from the freezing stress despite a lack of visible needle injury. Net photosynthesis and conductance remained lower in non-visibly injured frozen shoots compared to unfrozen shoots in late March and early April, more than 3 months after freezing. Initial net photosynthesis of frozen shoots placed in the growth chamber in late January was strongly correlated with maximum net photosynthesis. Initial net photosynthesis divided by initial conductance ( A i / g i ) was even more strongly correlated with maximum net photosynthesis ( r =0.95. A i / g i was also negatively correlated with visible needle injury estimated in late March. A i / g i measured on detached shoots, under favorable conditions for photosynthesis, may therefore be an early indicator of either latent visible needle injury or reduced photosynthetic capacity for freeze-damaged trees.

Evaluation of the effects of ozone and acidic precipitation, alone and in combination, on the photosynthesis, nutrition, and growth of red spruce and sugar maple.

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.