Walter W. Heck

Bio: Walter W. Heck is an academic researcher from North Carolina State University. The author has contributed to research in topics: Air quality index & Water content. The author has an hindex of 20, co-authored 41 publications receiving 1571 citations.

An Open-Top Field Chamber to Assess the Impact of Air Pollution on Plants

Abstract: Reasonable air pollution control policies depend upon a comparison of the costs of air pollution losses with the costs of controls. Present estimates of national economic losses to agricultural and ornamental vegetation are based primarily on field observations and partially on growth and yield data obtained from closed-top field chambers and greenhouses. This research describes the design and evaluation of an open-top field chamber that was developed to provide an environment more closely resembling ambient conditions than the environment found in closed-top chambers. Temperature and relative humidity within open-top chambers were similar to ambient conditions. Direct sunlight reached the plants for a portion of each day and rain entered, although not always uniformly over the chamber base. Chambers receiving charcoal-filtered air protected sensitive ‘Bel W₃’ tobacco plants (Nicotiana tabacum L.) from ambient ozone concentrations. Plants growing in chambers receiving unfiltered air or in ambient air plots were severely injured.

Factors Influencing Expression of Oxidant Damage to Plants

Abstract: This paper suggests that the mechanism that controls resistance of plants to oxidant pollutants may be similar to the one that controls resistance to other extremes in environmental factors. From the literature the following generalizations can be made in regard to the factors that affect the sensitivity of plants to oxidant air pollutants during growth: plants are more sensitive when grown under a short photo-period, a long dark period prior to exposure increases sensitivity; plants grown under low light intensities are more sensitive to ozone and less sensitive to PAN; low temperatures for one to several days prior to exposure reduce sensitivity; plants grown under drought conditions are less sensitive; plants grown under relatively low fertility levels are more sensitive. Sensitivity at time of exposure increases with increasing light intensity. Sensitivity of plants exposed under natural conditions is affected more by light intensity than by temperature. Temperature has an inverse effect on sensitivity, when plants are exposed under controlled lighting conditions. High carbon dioxide levels, at time of exposure, reduce sensitivity. Plants exposed under any soil conditions that produce a water stress in the plant show an increased resistance. Plant sensitivity, at time of exposure, increases with an increase inmore » humidity. Injury from PAN is mediated by a light-sensitive system within the plant. Sulfur dioxide reacts synergistically, with both ozone and nitrogen dioxide, on sensitive plant tissues. 101 references.« less

Design and Performance of a Large, Field Exposure Chamber to Measure Effects of Air Quality on Plants

Abstract: A 4.66-m diam., 3.6 m tall, cylindrical open-top field chamber was designed, constructed, and tested as a tool to measure the effects of air quality on plant function and yield. It is a larger version of the 3-m diam. chamber that has been used to measure the effects of gaseous pollutants on crop plants. The new chamber has an aluminum-channel frame covered with clear polyvinyl chloride plastic film. It is equipped with a frustum (truncated cone) that decreases ambient air ingress and can be fitted with a device to exclude rain (rain cap) for studies with simulated rain pH. During the daylight hours, the mean air temperature within the chamber was 0.6 °C greater than ambient on cloudy, cold days, 2.2 °C greater than ambient on partly cloudy, cool days, and 2.8 °C greater than ambient on sunny, warm days. The mean dew point temperature for a wide range of conditions was 0.7 ° greater inside than outside. Mean solar radiation in the chamber, with new plastic panels, was 15% less than ambient with a rain cap and 12% less with no rain cap. Charcoal filtration removed 78% of the O₃ in ambient air; long-term measurements during charcoal filtration showed that the mean O₃ concentration in the chamber (all positions and heights) was 77% less than ambient suggesting little or no long-term ingress through the top. Short-term gradients in O₃ concentrations existed (mostly near the top of the chamber) during infrequent periods of strong winds. During addition of approximately 0.09 µL L⁻¹ of O₃ to nonfiltered air, the mean (14-d) O₃ concentrations across all positions and heights varied by less than 0.005 µL L⁻¹ of the overall mean. Cooperative investigations of the USDA-ARS and the North Carolina State Univ. Paper no. 11974 of the Journal Series of the North Carolina Agric. Res. Serv., Raleigh, NC 27695-7643. This Research was partly supported by funds provided by the Southern Commercial Forest Res. Coop. within the joint USEPA-USDA Forest Service Response Program in cooperation with the National Council of the Pulp and Paper Industry for Air and Stream Improvement. The Forest Response Program is part of the National Acid Precipitation Assessment Program. This paper has not been subject to USEPA or Forest Service peer review and should not be construed to represent the policies of either Agency. The use of trade names in this publication does not imply endorsement by the North Carolina Agric. Res. Service or the USDA of the products named, nor criticism of similar ones not mentioned.

Ozone: nonlinear relation of dose and injury in plants.

Abstract: Ozone produces a sigmoidal dose-injury response in sensitive tobacco and pinto bean. A definite threshold concentration and presentation time are required before injury is initiated.

Interactions of environmental factors on the sensitivity of plants to air pollution.

Abstract: Before potential damage to vegetation can be adequately forecast, even after an air pollution alert has been placed in effect, a clear understanding of the interactions of environment on plant sensitivity must be ascertained. This involves detailed study of single factors and then multiple factors using the phytotoxicants in question. Factors studied or suggested include light (quality, intensity, and duration), temperature, carbon dioxide concentration, humidity, wind, soil moisture, soil aeration, nutrient levels, and soil texture. This paper presents a review of the work relating plant injury to specific air pollutants as conditioned by several environmental conditions supported by research on the interactions of ozone with these environmental conditions.

Rising atmospheric carbon dioxide: plants FACE the future

Abstract: Atmospheric CO(2) concentration ([CO(2)]) is now higher than it was at any time in the past 26 million years and is expected to nearly double during this century. Terrestrial plants with the C(3) photosynthetic pathway respond in the short term to increased [CO(2)] via increased net photosynthesis and decreased transpiration. In the longer term this increase is often offset by downregulation of photosynthetic capacity. But much of what is currently known about plant responses to elevated [CO(2)] comes from enclosure studies, where the responses of plants may be modified by size constraints and the limited life-cycle stages that are examined. Free-Air CO(2) Enrichment (FACE) was developed as a means to grow plants in the field at controlled elevation of CO(2) under fully open-air field conditions. The findings of FACE experiments are quantitatively summarized via meta-analytic statistics and compared to findings from chamber studies. Although trends agree with parallel summaries of enclosure studies, important quantitative differences emerge that have important implications both for predicting the future terrestrial biosphere and understanding how crops may need to be adapted to the changed and changing atmosphere.

Free-air Carbon Dioxide Enrichment (FACE) in Global Change Research: A Review

Abstract: Summary There have been many experimental studies to evaluate the response of vegetation to the effect of increases in the partial pressure of carbon dioxide in the atmosphere (p CO2) that are expected to occur during the next century. This knowledge is important for the future protection of food supplies, for understanding changes in natural ecosystems and for quantifying the role of terrestrial plants in regulating the rate of change of p CO2 and resulting changes in the global climate. Most of our knowledge about these effects has derived from experimental studies that have used open-top or closed chambers. These methods are subject to “chamber effects” caused by differences in energy balance and water relations that may significantly modify the response of vegetation to elevated p CO2. The small plot sizes imposed by these techniques add other limitations both to interpretation of results and scope of investigations. Free-air carbon dioxide enrichment (FACE) provides an experimental technique for studying the effects of elevated p CO2 on vegetation and other ecosystem components in large unenclosed plots (>20 m diameter). FACE avoids many modifications to the microclimate imposed by chamber methods and therefore provides some of the most reliable estimates of plant response to elevated p CO2. Control of p CO2 in large-scale FACE experiments has now been developed to an extent where performance is similar to that achieved with sophisticated closed-chamber facilities. Experience has shown that, when FACE facilities are fully utilised, the cost per unit of usable ground area enriched with CO2, is significantly lower than alternative methods. The large scale of FACE plots can support a range of integrated studies on the same material, thereby achieving a more complete analysis than has been possible with other methods of elevating p CO2. This review considers the technical aspects of FACE methodology, outlines the major FACE experiments and summarises the advances in understanding of p CO2 effects on ecosystems that it has allowed. Published data on large-scale FACE experiments with adequate plot replication are limited to experiments on four crop/vegetation types at three locations. FACE has been used for experiments on two crops, cotton and wheat, at Maricopa, Arizona, and on grassland species, principally ryegrass and clover, at Eschikon, Switzerland. The method has also been adapted for the first study of mature forest trees, loblolly pine at Duke Forest, North Carolina. A number of other large-scale FACE experiments are in progress and the method has been adapted for use in much smaller experimental plots. The results of the major FACE experiments represent important advances over understanding obtained from previous p CO2 treatment methods. Most significant in terms of the global climate and atmosphere system are the clear observations with cotton and wheat crops that elevated p CO2 increases the ratio of sensible: latent heat transfer and causes daytime warming of the surface vegetation. This results from decreased water use and loss, and has been evident at a range of scales. The scale of FACE plots has allowed quantitative and detailed studies of the dynamics of below-ground production and C accumulation in a range of systems, and all have shown surprisingly large increases. Of particular note are the increases observed in grassland grown with low N, where there was no response of the above-ground biomass, but an increased rate of turnover of leaves and input of surface litter. FACE has allowed cultivation of crops at a scale appropriate to agronomic trials and shown statistically significant increases in the yields of wheat, cotton and pasture crops, although some of these increases are less than suggested by chamber experiments. Against expectations, the FACE experiments at Maricopa have shown a greater relative increase in yield in crops grown under water shortage than in water-sufficient crops. Acclimatory loss of photosynthetic capacity has been widely anticipated to offset the increase in photosynthesis that follows initial transfer of vegetation to elevated p CO2. None of the FACE experiments provides any evidence of such a loss; however, changes which will allow a re-optimisation of N distribution within plants have been reported. FACE methods have now been demonstrated to be feasible and effective within a range of crops and vegetation types. The information from past experiments has greatly improved our understanding of the impacts of global atmospheric change on terrestrial ecosystems.

Coumarin-Based Small-Molecule Fluorescent Chemosensors.

Abstract: Coumarins are a very large family of compounds containing the unique 2H-chromen-2-one motif, as it is known according to IUPAC nomenclature. Coumarin derivatives are widely found in nature, especially in plants and are constituents of several essential oils. Up to now, thousands of coumarin derivatives have been isolated from nature or produced by chemists. More recently, the coumarin platform has been widely adopted in the design of small-molecule fluorescent chemosensors because of its excellent biocompatibility, strong and stable fluorescence emission, and good structural flexibility. This scaffold has found wide applications in the development of fluorescent chemosensors in the fields of molecular recognition, molecular imaging, bioorganic chemistry, analytical chemistry, materials chemistry, as well as in the biology and medical science communities. This review focuses on the important progress of coumarin-based small-molecule fluorescent chemosensors during the period of 2012-2018. This comprehensive and critical review may facilitate the development of more powerful fluorescent chemosensors for broad and exciting applications in the future.

The effect of air pollutants on physiological processes in plants

Abstract: . Important physiological processes, photosynthesis, respiration, carbon allocation and stomatal function are known to be affected by air pollutants. A wide range in sensitivity of photosynthesis both within and between species is evident from the literature for the pollutants sulphur dioxide, ozone, nitrogen oxide and hydrogen fluoride. Some of this variation is clearly due to genetic factors, but much is in response to differences in environmental conditions both prior to and during fumigation. Exposure of plants to mixtures of pollutants generally reduced the threshold at which effects were first detected and increased the level of inhibitory responses. In the majority of studies on stomatal responses to air pollutants, opening occurs at low concentrations, below the threshold for effects on photosynthesis, and closure occurs at injurious concentrations; this latter response often following the inhibition of photosynthesis. Effects on carbon allocation have been reported in response to air pollutants. Changes usually favour leaf development over root growth, which can compensate for a decline in net assimilation rate up to a certain point but may limit water uptake from soils with low moisture content. Future research into physiological effects of air pollutants should incorporate an integrated approach in which both key physiological parameters and growth parameters are measured together with estimates of the effective dose of pollutant. In this way, the underlying mechanisms to changes in growth and development will be more fully understood.

Crop responses to ozone: uptake, modes of action, carbon assimilation and partitioning

Abstract: The inhibitory effects of tropospheric O 3 on crop photosynthesis, growth, and yield have been documented in numerous studies over the past 35 years. In large part, the results of this research supported governmental regulations designed to limit tropospheric O 3 levels to concentrations that affected crop production at economically acceptable levels. Recent studies have brought into question the efficacy of these concentration-based O 3 standards compared with flux-based approaches that incorporate O 3 uptake along with environmental and biotic factors that influence plant responses. In addition, recent studies provide insight into the biochemical mechanisms of O 3 injury to plants. Current interpretations suggest that upon entry into the leaf intercellular space O 3 rapidly reacts with components of the leaf apoplast to initiate a complex set of responses involving the formation of toxic metabolites and generation of plant defence responses that constitute variably effective countermeasures. Plant species and cultivars exhibit a range of sensitivity to O 3 , evident as heritable characteristics, that must reflect identifiable biochemical and molecular processes that affect sensitivity to O 3 injury, although their exact makeup remains unclear. Ozone clearly impairs photosynthetic processes, which might include the effects on electron transport and guard cell homeostasis as well as the better-documented effects on carbon fixation via decreased Rubisco activity. Translocation of photosynthate could be inhibited by O 3 exposure as well. Further, the influence of tropospheric O 3 needs to be considered when assessing potential effects of rising concentrations of atmospheric CO 2 on crop production. Advances in O 3 flux modelling and improved understanding of biochemical and molecular effects of O 3 on photosynthetic gas exchange and plant defence processes are leading to more complete, integrated assessments of O 3 impacts on crop physiology that continue to support the rationale for maintaining or improving current O 3 air quality standards as well as providing a basis for development of more O 3 -tolerant crop lines.