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    Author(s): Robert L. Heath
    Date: 1998
    Source: In: Bytnerowicz, Andrzej; Arbaugh, Michael J.; Schilling, Susan L., tech. coords. Proceedings of the international symposium on air pollution and climate change effects on forest ecosystems. Gen. Tech. Rep. PSW-GTR-166. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 11-17
    Publication Series: General Technical Report (GTR)
    Station: Pacific Southwest Research Station
    PDF: View PDF  (190 KB)

    Description

    Urban air basin produced oxidants, notably ozone, induce a decline in productivity in plants. This loss of productivity is manifested by slower growth, hindered development, lower reproduction rates, impaired ability to resist disease, and other stresses. While many metabolic events have been linked to oxidant exposure, three major shifts have been well-studied: increased production and more rapid turnover of antioxidant systems; production of symptoms similar to a mechanical wounding of the tissue, especially ethylene production; and decline in photosynthesis. Although these processes may be linked metabolically at a fundamental level, the mechanisms leading to a decline in photosynthesis have been shown to directly lower plant productivity. There are two distinct changes in physiology which can directly alter the photosynthetic rate by leaves: a closure of the stomata limiting CO2 concentration, and a decline in the ability to fix CO2 within the chloroplast. In many studies it is difficult to discriminate which is more critical and which triggers various effects because in the final analysis, both limit carbon assimilation. The mechanisms of stomatal closure may be linked to the loss of membrane permeability and transport because of oxidation of membrane channels and transport proteins and/or oxidation to an increased sensitivity of the stomata to closure signals, such as internal Ca2+ levels or abscisic acid. On the other hand, impairment of the processes of photosynthesis is probably not caused by changes in the light gathering photosystems, but rather by a loss of CO2 fixing ability induced by a decline in Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) or by an alteration in normal metabolite flow via changes in ionic balance. It is not yet clear which of these mechanism is more critical to each individual plant species under varied environmental conditions. However, the loss of photosynthetic products is only the first step in the loss of productivity. Much evidence indicates that translocation of the fixed carbon is altered by oxidants. Because translocation is very sensitive to energy and carbohydrate status as well as membrane function of the leaf, phloem loading would also be at risk by oxidant exposure. A decline in carbohydrate levels to roots and growing shoot tips would have profound effects upon the plant's ability to grow and respond normally to the integrated effects of the remainder of the environment.

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    Citation

    Heath, Robert L. 1998. Oxidant induced alteration of carbohydrate production and allocation in plants. In: Bytnerowicz, Andrzej; Arbaugh, Michael J.; Schilling, Susan L., tech. coords. Proceedings of the international symposium on air pollution and climate change effects on forest ecosystems. Gen. Tech. Rep. PSW-GTR-166. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 11-17

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