Atmospheric concentrations of carbon dioxide (CO2) have significantly increased over the past century and are expected to continue rising in the future. While elevated levels of CO2 will likely result in higher crop yields, weed growth is also highly likely to increase, which could increase the incidence of herbicide resistant biotypes. An experiment was conducted in 2012 to determine the effects of an elevated CO2 environment on glyphosate and halosulfuron efficacy for postemergence control of purple and yellow nutsedge (Cyperus rotundus L. and C. esculentus L.). Both species of nutsedge where grown in 3.0-L containers under either ambient or elevated (ambient + 200 µmol mol-1) CO2 in open-top field chambers and treated with either 0.5×, 1.0×, or 1.5× of the manufacturer’s labeled rate of halosulfuron, glyphosate, or a tank mix of the two herbicides. The growth of both nutsedge species responded positively to elevated CO2, purple nutsedge had increased shoot and root dry weights and yellow nutsedge had increased shoot, root, and tuber dry weights and counts. Few treatment differences were observed among the herbicides at any of the rates tested. At three weeks following herbicide application, both purple and yellow nutsedge were adequately controlled by both herbicides and combinations at all rates tested, regardless of CO2 concentration. Based on this study, it is likely that predicted future CO2 levels will have little impact on the efficacy of single applications of halosulfuron or glyphosate for control of purple and yellow nutsedge at the growth stages described here, although scenarios demanding more persistent control efforts remain a question.

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Control of yellow and purple nutsedge in elevated CO2 environments with glyphosate and halosulfuron.

The light-dependent generation of active oxygen species is termed photooxidative stress. This can occur in two ways: (1) the donation of energy or electrons directly to oxygen as a result of photosynthetic activity; (2) exposure of tissues to ultraviolet irradiation. The light-dependent destruction of catalase compounds the problem. Although generally detrimental to metabolism, superoxide and hydrogen peroxide may serve useful functions if rigorously controlled and compartmentalised. During photosynthesis the formation of active oxygen species is minimised by a number of complex and refined regulatory mechanisms. When produced, active oxygen species are eliminated rapidly by efficient antioxidative systems. The chloroplast is able to use the production and destruction of hydrogen peroxide to regulate the thermal dissipation of excess excitation energy. This is an intrinsic feature of the regulation of photosynthetic electron transport. Photoinhibition and photooxidation only usually occur when plants are exposed to stress. Active oxygen species are part of the alarm-signalling processes in plants. These serve to modify metabolism and gene expression so that the plant can respond to adverse environmental conditions, invading organisms and ultraviolet irradiation. The capacity of the antioxidative defense system is often increased at such times but if the response is not sufficient, radical production will exceed scavenging and ultimately lead to the disruption of metabolism. Oxidative damage arises in high light principally when the latter is in synergy with additional stress factors such as chilling temperatures or pollution. Environmental stress can modify the photooxidative processes in various ways ranging from direct involvement in light-induced free radical formation to the inhibition of metabolism that renders previously optimal light levels excessive. It is in just such situations that the capacity for the production of active oxygen species can exceed that for scavenging by the antioxidative defense systems. The advent of plant transformation, however, may have placed within our grasp the possibility of engineering greater stress tolerance in plants by enhancement of the antioxidative defence system.

Photooxidative stress in plants

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.

Rising atmospheric carbon dioxide: plants FACE the future

Changes in temperature, CO 2 , and precipitation under the scenarios of climate change for the next 30 yr present a challenge to crop production. This review focuses on the impact of temperature, CO 2 , and ozone on agronomic crops and the implications for crop production. Understanding these implications for agricultural crops is critical for developing cropping systems resilient to stresses induced by climate change. There is variation among crops in their response to CO 2 , temperature, and precipitation changes and, with the regional differences in predicted climate, a situation is created in which the responses will be further complicated. For example, the temperature effects on soybean [Glycine max (L.) Merr.] could potentially cause yield reductions of 2.4% in the South but an increase of 1.7% in the Midwest. The frequency of years when temperatures exceed thresholds for damage during critical growth stages is likely to increase for some crops and regions. The increase in CO 2 contributes significantly to enhanced plant growth and improved water use efficiency (WUE); however, there may be a downscaling of these positive impacts due to higher temperatures plants will experience during their growth cycle. A challenge is to understand the interactions of the changing climatic parameters because of the interactions among temperature, CO 2 , and precipitation on plant growth and development and also on the biotic stresses of weeds, insects, and diseases. Agronomists will have to consider the variations in temperature and precipitation as part of the production system if they are to ensure the food security required by an ever increasing population.

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Climate Impacts on Agriculture: Implications for Crop Production

Pigments are present in all living matter and provide attractive colors and play basic roles in the development of organisms. Human beings, like most animals, come in contact with their surroundings through color, and things can or cannot be acceptable based on their color characteristics. This review presents the basic information about pigments focusing attention on the natural ones; it emphasizes the principal plant pigments: carotenoids, anthocyanins, and betalains. Special considerations are given to their salient characteristics; to their biosynthesis, taking into account the biochemical and molecular biology information generated in their elucidation; and to the processing and stability properties of these compounds as food colorants.

Natural Pigments: Carotenoids, Anthocyanins, and Betalains — Characteristics, Biosynthesis, Processing, and Stability

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.

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

A reassessment of crop loss from ozone.

Described are new methods for dispensing and monitoring ozone in open top field chambers; such chambers are used in studies of the effects of oxidants on plants. One system semi-automatically dispenses and automatically monitors ozone in multiple open top field chambers at distances as far as 106 m. Effects of the chambers on air velocity, light, temperature, ozone distribution, and plant growth are determined. Various gaseous pollutants could be monitored with minor modifications to the system. Although open top chambers affect the plant environment, the effects are fewer than those induced in closed chamber designs. (4 diagrams, 17 references, 5 tables)

Dispensing and monitoring ozone in open-top field chambers for plant-effects studies.

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)

A Field Technique for the Study of Plant Responses to Elevated Carbon Dioxide Concentrations

A principal objective of the National Crop Loss Assessment Network (NCLAN) is to develop O/sub 3/ dose-crop yield response models for use in assessing the effects of O/sub 3/ on economically important crop species and cultivars. This paper is part of a third assessment report from NCLAN. The NCLAN is composed of several cooperating programs with field sites in different regions of the country. Open-top chambers allow control of O/sub 3/ concentration-crop yield functions for the major crops studied in 1980 and 1981, and for all crops studied during 1982. Four O/sub 3/ averaging times (exposure statistics) are used in a Weilbull model for each experimental data set. Models derived using two seasonal mean O/sub 3/ statistics (1-h/day and 7-h/day means) and two seasonal peak O/sub 3/ statistics (1-h and 7-h) are compared. The results suggest that all four O/sub 3/ statistics are of similar value when obtained from and used for the same data set. Seasonal mean O/sub 3/ statistics can be used to develop models which can be used to estimate yield of a given crop from data obtained from different sites or from different years at one site. However, peak statistics obtained from one site cannot bemore » used to predict yield from data obtained at a second site, or from data obtained at the same site in different years. 12 references, 4 tables.« less

Allen S. Heagle

Papers

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

A reassessment of crop loss from ozone.

Dispensing and monitoring ozone in open-top field chambers for plant-effects studies.

A Field Technique for the Study of Plant Responses to Elevated Carbon Dioxide Concentrations

Assessing Impacts of Ozone on Agricultural Crops: II. Crop Yield Functions and Alternative Exposure Statistics