Allen S. Heagle

A field technique for the study of plant responses to elevated carbon dioxide concentrations

Field techniques that would permit the study of elevated CO/sub 2/ levels on plants are described. The design, construction, and testing of a system for dispensing and monitoring CO/sub 2/ in the number of open top chambers are discussed. (JMT)

Catechin, proanthocyanidin and lignin contents of loblolly pine (Pinus taeda) needles after chronic exposure to ozone

Concentrations of soluble and bound phenolic compounds were measured in needles of 3-yr-old loblolly pine (Pinus taeda L.) trees exposed from May to November 1993 to a range of ozone (O3 ) concentrations in open-top field chambers, The treatments were charcoal-filtered air (CF). non-filtered air (NF), and NF air with O2 added at 1.5 times (NF 1.5) and 2(1 times (NF 2.0) the ambient O., concentration for 12 h daily. Average daily (0800-2000 hours) O3 concentrations in the CF. NF. NF 1.5 and NF 20 treatments were. 29. 47, 76 and 98 nl 1(-1) . respectively, for the 140 d treatment period. At the end of the treatment period, total phenolic and proanthocyanidin concentrations in the previous years needles were 25-29% higher in the NF 2.0 treatment compared with the lower O3 treatments. Catechin concentration increased in the previous years needles by as much as 81 % between the NF 2.0 treatment and the lower O3 treatments. Catechin is an effective antioxidant, and elevated levels might confer some protection against O3 injury. No significant differences in total phenolics and proanthocyanidins in the previous years needles were detected among the remaining treatments, or among any O3 treatment for the current years needles. Lignin content in needles of both years was not significantly affected by O3 exposure. Chances in the phenolic content of older needles in response to elevated O3 could alter plant-pathogen interactions and slow down microbiol decomposition, which could contribute to a decline in site soil quality.

Effects of vegetation: native, crops, forests

Publisher Summary This chapter presents an update of research on the effects of air pollutants on vegetation. It discusses the primary data base for the two pollutants of primary concern to terrestrial ecosystems—ozone and sulfur dioxide. The chapter highlights research areas, discusses the relative importance of other pollutants, and covers some research areas that are receiving little attention at present. It focuses on two areas of critical worldwide interest. It is a synthesis of the understanding of the impact of acidic deposition on terrestrial systems. The chapter discusses the state of the art in regional and national assessment methodology, using an ongoing program as an example. It focuses on ozone and crop production and addresses research with sulfur dioxide and research on forest systems.

Gas exchange in open-top field chambers—I. Measurement and analysis of atmospheric resistances to gas exchange

Abstract Factors controlling rates of gas exchange between the atmosphere and plants growing in open-top field chambers, commonly used for studying crop responses to air quality, are measured and analysed. Restrictions on gas transfer by incursion through the open top, by air movement from the ventilation fan and by transfer through the leaf boundary layer are described by a resistance analogue. A method of measuring incursion resistance r i , using sulphur hexafluoride is described and applied to chambers of a standard design and of a design with a truncated conical top. There was a well-defined variation of r i with windspeed for the modified design and r i , decreased for a given windspeed as crop height increased. Leaf boundary layer resistance r b was measured in both chamber designs and was analysed as a function of incursion and fan ventilation rate. Values of r b in chambers may be lower than in crop canopies in the field, and possible consequences of this difference are discussed.

Gas exchange in open-top field chambers—II. Resistances to ozone uptake by soybeans

Abstract A method is described for measuring the rate of removal of O 3 from air in an open-top field chamber used for exposing soybeans to O 3 . Measurements are analysed to derive resistances to removal by the chamber walls, soil and the leaf canopy. Combined wall and soil resistances exceeded 300 s m −1 . Canopy resistances of well-watered plants by day averaged 73 s m −1 , comparable with published measurements in the field by micrometeorological methods. When plants were water-stressed, canopy resistances by day increased to 200–300 s m −1 ; at night, when stomata were closed, canopy resistances exceeded 350 s m −1 . The method should be applicable for measuring fluxes of CO 2 , and water vapour as well as other pollutant gases.

Effects of chronic doses of ozone on field-grown loblolly pine: seedling responses in the first year

A study was designed to examine responses of loblolly pine (Pinus taeda) to chronic exposure to ozone (O/sub 3/) in the field. Seedlings of four full-sib families of loblolly pine were planted in a field near Raleigh, NC, and exposed daily (May 27 to October 24, 1985) in open-top chambers to O/sub 3/ ranging from 0.5 to 1.96 times the O/sub 3/ concentration in non-filtered (NF) air. One-fourth of the plants in each plot were removed during each of two harvest (August and October) to measure effects of O/sub 3/ on plant growth. Plants of each family exhibited foliar symptoms characteristic of O/sub 3/ injury after five months of exposure to any greater-than-ambient O/sub 3/ concentration, and one family exhibited symptoms after five months of exposure to NF air. Ozone dose-plant response relationships were quantified by regression for stem height, stem diameter, biomass, and other plant morphological and yield characteristics. All relationships were linear for three families, but one family exhibited no significant growth response relationship of O/sub 3/ dose. Dose-response equations suggest a maximum growth suppression of 10 percent for NF air compared to charcoal-filtered air in the first season of exposure.

Effects of Carbon Dioxide Enrichment on Leaf Chemistry and Reproduction by Twospotted Spider Mites (Acari: Tetranychidae) on White Clover

Abstract Plant growth and yield responses to carbon dioxide (CO2) enrichment are well established. Much less is known of the response of arthropod pests to CO2 enrichment. Reproductive response of twospotted spider mites (Tetranychus urticae Koch) on white clover (Trifolium repens L.) to a range of CO2 concentrations was measured. The CO2 treatments were applied for 24 h d−1 at ≈395, 484, 570, 657, and 748 μLL−1 on the 14 d before and 26–27 d after infestation with mites. Eggs, larvae, nymphs, and adult mites were removed from leaves and counted 27–29 d after infestation. Leaf area and weight were measured, and leaves were analyzed to measure structural and nonstructural carbohydrates, N, amino acids and digestibility. Carbon dioxide enrichment caused linear increases in plant growth and foliar nonstructural carbohydrates, but caused linear decreases in foliar N. Carbon dioxide enrichment significantly increased the rate of mite reproduction on both clover clones. Correlations between mite population increase were significantly positive for foliar nonstructural carbohydrates and significantly negative for foliar N. Concentrations of ambient CO2 expected in the 21st century may increase the risk of mite population damage on some plant species.

Development of a multi-factor model for predicting the effects of ambient ozone on the biomass of white clover

Results are presented from the UN/ECE ICP Vegetation (International Cooperative Programme on effects of air pollution on natural vegetation and crops) experiments in which ozone(O(3))-resistant (NC-R) and -sensitive (NC-S) clones of white clover (Trifolium repens cv. Regal) were exposed to ambient O(3) episodes at 14 sites in eight European countries in 1996, 1997 and 1998. The plants were grown according to a standard protocol, and the forage was harvested every 28 days for 4-5 months per year by excision 7 cm above the soil surface. Biomass ratio (NC-S/NC-R) was related to the climatic and pollutant conditions at each site using multiple linear regression (MLR) and artificial neural networks (ANNs). Twenty-one input parameters [e.g. AOT40, 7-h mean O(3) concentration, daylight vapour pressure deficit (VPD), daily maximum temperature] were considered individually and in combination with the aim of developing a model with high r(2) and simple structure that could be used to predict biomass change in white clover. MLR models were generally more complex, and performed less well for unseen data than non-linear ANN models. The ANN model with the best performance had five inputs with an r(2) value of 0.84 for the training data, and 0.71 for previously unseen data. Two inputs to the model described the O(3) conditions (AOT40 and 24-h mean for O(3)), two described temperature (daylight mean and 24-h mean temperature), and the fifth input appeared to be differentiating between semi-urban and rural sites (NO concentration at 17:00). Neither VPD nor harvest interval was an important component of the model. The model predicted that a 5% reduction in biomass ratio was associated with AOT40s in the range 0.9-1.7 ppm x h (microl l(-1) h) accumulated over 28 days, with plants being most sensitive in conditions of low NO(x), medium-range temperature, and high 24-h mean O(3) concentration.

Elevated Carbon Dioxide and Ozone Effects on Peanut: I. Gas-Exchange, Biomass, and Leaf Chemistry

The effects of elevated CO2 and ozone (O3) on net photosynthetic rate (A) and growth are generally antagonistic although plant responses are highly dependent on crop sensitivity to the individual gases and their concentrations. In this experiment, we evaluated the effects of various CO2 and O3 mixtures on leaf gas-exchange, harvest biomass, and leaf chemistry in peanut (Arachis hypogaea L.), an O3-sensitive species, using open-top field chambers. Treatments included ambient CO2 (about 375 micromol mol-1) and CO2 enrichment of approximately 173 and 355 micromol mol-1 in combination with charcoal-filtered air (22 nmol O3 mol-1), nonfiltered air (46 nmol O3 mol-1), and nonfiltered air plus O3 (75 nmol O3 mol-1). Twice-ambient CO2 in charcoal-filtered air increased A by 23% while decreasing seasonal stomatal conductance (gs) by 42%. Harvest biomass was increased 12 to 15% by elevated CO2. In ambient CO2, nonfiltered air and added O3 lowered A by 21% and 48%, respectively, while added O3 reduced gs by 18%. Biomass was not significantly affected by nonfiltered air, but was 40% lower in the added O3 treatment. Elevated CO2 generally suppressed inhibitory effects of O3 on A and harvest biomass. Leaf starch concentration was increased by elevated CO2 and decreased by O3. Treatment effects on foliar N and total phenolic concentrations were minor. Increasing atmospheric CO2 concentrations should attenuate detrimental effects of ambient O3 and promote growth in peanut but its effectiveness declines with increasing O3 concentrations.

Ranking of soybean cultivars for resistance to ozone using different ozone doses and response measures

Abstract The relative resistance (ranking) of soybean Glycine max (L.) Merr. cultivars Dare, Hood, Lee 68 and Scott to ozone (O 3 ) was affected by the O 3 concentration, duration of exposure and the response measure selected as the criterion for ranking. The ranking of cultivars obtained by exposure to chronic doses of O 3 was often different from that obtained by exposure to acute doses. Rankings based on growth effects were usually different from those based on foliar injury. Rankings based on primary leaf injury sometimes differed from those based on trifoliate leaf injury. The results show a need for further work in order to develop methods of screening cultivars for resistance to O 3 .