Submitted to: Plant Cell and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2002
Publication Date: 5/1/2003
Citation: ZHAO, D., REDDY, K.R., KAKANI, V.G., READ, J.J., SULLIVAN, J.H. GROWTH AND PHYSIOLOGICAL RESPONSES OF COTTON (GOSSYPIUM HIRSUTUM L.) TO ELEVATED CARBON DIOXIDE AND ULTRAVIOLET-B RADIATION UNDER CONTROLLED ENVIRONMENTAL CONDITIONS. PLANT CELL AND ENVIRONMENT. 2003. v.26.p.771-782. Interpretive Summary: Carbon dioxide (CO2) is an important greenhouse gas and its increase in the atmosphere is known to enhance growth and photosynthesis in cotton, and other C3 crop species. As a result of stratospheric ozone depletion, ultraviolet-B radiation (280-320 nm) is expected to increase at ground level, and may cause plant damage due to inhibition of photosynthesis, degradation of protein, and increased oxidative stress. Plant sensitivity to UV-B radiation varies among species and is influenced by environment, including CO2. We conducted a growth chamber study to determine the interactive effects of CO2 and UV-B radiation on cotton growth and physiology. Six treatment levels were studied from plant emergence to maturity, and comprised 360 (ambient) and 720 mol CO2 mol-1 (elevated), and three daily UV-B intensities of 0, 8 (the present level commonly observed in southeastern USA) and 16 kJ m-2 within each CO2 level. Elevated CO2 increased leaf photosynthesis, water-soluble carbohydrate concentration, and plant dry matter accumulation. However, the detrimental effects of high UV-B on flower and fruit development could not be alleviated by elevated CO2. Decreased number of fruits in cotton exposed to UV-B radiation suggests breeding UV-B radiation-tolerant cultivars is important even in current ambient levels of CO2 and UV-B radiation. Results suggest plant physiological functions are most impaired by a doubling of present ambient levels of UV-B radiation.
Technical Abstract: Cotton (Gossypium hirsutum L.) response to projected climate change may involve either increases or decreases in growth and yield. We conducted studies in six Soil-Plant-Atmosphere-Research (SPAR) units to determine the interactive effects of carbon dioxide (CO2) and ultraviolet-B (UV-B) radiation on cotton physiology. Six treatments were comprised of two CO2 levels (360 and 720 mol mol-1) and three UV-B levels of 0 (control), 8, and 16 kJ m-2 d-1 biologically effective radiation within each CO2 level. Treatments were imposed from emergence to three weeks after first flower stage. Plant height, leaf area, dry weight accumulation, photosynthesis and leaf carbohydrates were greater at elevated CO2 than at ambient CO2. The highest UV-B level decreased leaf area, length of fruiting branches and plant height. Changes in height were related to decreased internode length rather than number of mainstem nodes. Fruit (boll) dry weight accumulation was most sensitive to UV-B,such that boll retention was significantly lower in 8 kJ m-2 d-1 UV-B radiation than controls, even though total dry matter and leaf photosynthesis did not differ between treatments. The highest UV-B level decreased total (43%) and fruit (88%) dry weight, possibly due to lower photosynthesis. Results indicate elevated CO2 did not ameliorate the adverse effects of UV-B radiation on cotton growth and physiology, particularly cotton fruit retention, which was most sensitive to UV-B radiation stress.