About |
(43 K) |
Effects of UV-B Radiation and Elevated Co2 on Cotton Plant Growth and Development
|
ABSTRACT Carbon dioxide concentration [CO2] and ultraviolet-B (UV-B, 280-320 nm) radiation at the Earths surface have been increasing due to human activities and depletion of stratospheric ozone. Changes in [CO2] and UV-B radiation directly or indirectly affect crop physiology, growth, development, and yield. Earlier studies have shown that elevated CO2 can increase photosynthesis of C3 crops, resulting in a significant increase in crop yields. Crop responses to UV-B depend on species, cultivar, UV-B dose, and duration of exposure. Cotton (Gossypium hirsiutum L.) responses to elevated CO2 have been well qualified, but little is known on the effects of increased UV-B radiation on cotton growth, development and physiology. Experiments were conducted in sunlit controlled environmental chambers known as Soil-Plant-Atmosphere-Research units in 2001 to determine interactive effects of atmospheric [CO2] and UV-B radiation on growth, development, and dry matter accumulation. Six treatments included two CO2 levels (360 and 720 μL L-1) and three biologically effective UV-B doses (0, 8, and 16 kJ m-2 d-1) within each CO2 level. Treatments were given from emergence through 3 weeks after the first flower stage. Results indicated that both elevated CO2 and UV-B radiation did not affect dates of squaring and flowering. Elevated CO2 increased plant height, leaf area, leaf net photosynthetic rate (Pn), and dry matter accumulation. Dry matter partitioning among plant organs, on the other hand, was not affected by [CO2]. High UV-B radiation (16 kJ m-2 d-1) mainly reduced plant height, fruiting branch length and leaf area. Decreased plant height was related to shorter internodes rather than the number of main-stem nodes. Fruit dry matter accumulation was most sensitive to UV-B radiation among plant organs. Under the UV-B of 8 kJ m-2 d-1, fruit dry weight was significantly lower than control (no UV-B) plants although there was no difference in total dry matter accumulation between the two treatments. The UV-B of 16 kJ m-2 d-1 reduced both total (43%) and fruit (88%) dry weights compared to the control. Reduction in total dry matter accumulation from the higher UV-B radiation was due to lower leaf Pn and smaller leaf area. Leaf Pn of plants treated with 8 kJ m-2 d-1 UV-B did not differ from that of control plants, whereas the Pn of plants exposed to 16 kJ m-2 d-1 UV-B decreased by 35% in 360 [.mu]L L-1 and 43% in 720 μL L-1 during fruiting. Decreased fruit dry weight from UV-B radiation was closely associated with higher fruit abscission or fewer bolls retained. Elevated CO2 did not alleviate the adverse effects of UV-B radiation on cotton growth and development. The plants grown under elevated CO2 (720 μL L-1) were even more sensitive to high UV-B radiation compared to the plants grown under ambient CO2 (360 μL L-1) level. |
©National Cotton Council, Memphis TN |
Document last modified May 20, 2002
|