Photosynthesis, Dark Respiration, and Growth of Rumex patientia L. Exposed to Ultraviolet Irradiance (288 to 315 Nanometers) Simulating a Reduced Atmospheric Ozone Column

Abstract

Net photosynthesis, dark respiration, and growth of Rumexpatientia L. exposed to a ultraviolet irradiance (288-315 nanometers) simulating a 0.18 atm-cm stratospheric ozone column were determined. The ultraviolet irradiance corresponding to this 38% ozone decrease from normal was shown to be an effective inhibitor of photosynthesis and leaf growth.The repressive action on photosynthesis accumulated through time whereas leaf growth was retarded only during the initial few days of exposure. Small increases in dark respiration rates occurred but did not continue to increase with longer exposure periods. A reduction in total plant dry weight and leaf area of approximately 50% occurred after 22 days of treatment, whereas chlorophyll concentrations remained unaltered.Global UV irradiance on the earth's surface fluctuates with changes in solar altitude, cloud cover, stratospheric ozone concentration, and atmospheric turbidity. No appreciable UV radiation below 295 nm is received on the earth's surface due to absorption of UV radiation by the stratospheric ozone layer. A reduction of the stratospheric ozone column would result in a predictable shift in the terrestrial global spectrum to include shorter UV wavelengths below 295 nm (3,13). Such a reduction could result from catalytic interactions of ozone with oxides of nitrogen released in the stratosphere by aircraft (14, 16), halomethanes diffusing from the troposphere (6, 15, 22) or other man-induced perturbations of the stratosphere. Although the resulting shift in the global UV radiation spectrum resulting from partial ozone reduction would be small (3, 13), any added increment of shorter wavelength UV radiation might prove significant since it is effectively absorbed by chromophores such as nucleic acids and proteins (11).Historically, UV radiation photobiological research has dealt principally with monochromatic 254-nm radiation. From these studies, an array of deleterious effects on plants has been shown.These effects include such responses as reduced growth (25) partial ozone reduction does not, at the present time, appear plausible for three reasons. First, biological response to UV radiation tends to be highly wavelength-specific with respect to efficiency of photobiological action (5, 11). Second, the biologically potent waveband shorter than 280 nm would not be transmitted to the earth's surface even if the ozone column were reduced to 40% of its present thickness (13). Finally, there may be qualitative as well as quantitative differences in the response to 254-nm radiation and radiation in the 288-to 315-nm waveband as has been reported for Chlamydomonas reinhardi (23).This paper reports on evaluation of net photosynthesis, dark respiration, and growth of Rumex patientia L. exposed to UV irradiation corresponding to the global UV spectral irradiance which would occur with partial ozone reduction. The level of ozone reduction simulated was approximately 38% from normal, and resulted in an almost immediate detrimental effect on those plant processes wh...

Ultraviolet-B Radiation-induced Inhibition of Leaf Expansion and Promotion of Anthocyanin Production

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“…It appears that inhibition of expansion is not entirely due to reduction of photosynthetic rates (23). It is important to elucidate the physiological mechanisms involved in UV-B radiation inhibition of leaf expansion and how these may interact with mechanisms known to control leaf expansion.…”

Inhibition of Seagrass Photosynthesis by Ultraviolet-B Radiation

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