4326:
Effect of GA3 and Ethephon On Photosynthesis of Wild Rhododendron Delavayi Franch

Wednesday, August 4, 2010
Springs F & G
Yin Yi , School of Life Sciences, Guizhou Normal University, Guiyang, China
Donglin Zhang , Univ of Maine, Orono, ME
Xun Chen , Guizhou Academy of Science, Guiyang, Guizhou, China
Xiaorong Xu , Guizhou Normal University, Guizhou, China
Ximin Zhang , School of Life Sciences, Guizhou Normal University, Guiyang, Guizhou, China
Qingfa Song , School of Life Sciences, Guizhou Normal University, Guiyang, Guizhou, China
Yubin Zhang , School of Life Sciences, Guizhou Normal University, Guiyang, Guizhou, China
Flowering and growth of wild populations of Rhododendron delavayi Franch. could be regulated using GA3 and ethephon. To better understand their effect, diurnal photosynthesis was monitored using portable LI-6400 photosynthesis system. The photosynthetic active radiations at the site were between 127.4-1257.3 µmol•m-2•s-1 and the temperatures ranged from 16.3 and 27.4C. Ambient CO2 concentrations were 307.1-390.4 µmol•mol-1 and the relative humidity was 80.3% at 7:30am. The results indicated that both GA3 and ethephon did not alternate the trend of diurnal photosynthesis rates. Under the treatments of 100, 200 mg•L-1 and control (just pure water), the first peak rates were 11.60, 10.1, 8.29 µmolCO2•m-2•s-1 at 11:30am and the 2nd peak rates were 9.41, 9.42, 7.42 µmolCO2•m-2•s-1 at 3:30pm, respectively. However, ethephon treatments reduced the photosynthesis rates. As ethephon concentration increased from 100 to 200 mg•L-1, the photosynthesis rate were much lower. Transpiration rate showed similar trend as the photosynthesis rate under all treatments. But, the highest rate, 4.62 mmolH2O•m-2•s-1, occurred under the treatment of GA3 200 mg•L-1 at 1:30pm. Compared with the control, plants spayed with GA3 at 100 mg•L-1 increased water use efficiency (WUE), while reduced WUE at GA3 200 mg•L-1.  Stomata conductance and stomata limitation followed the same trend as the photosynthesis rates. When spaying GA3 on Rh. delavayi, intercellular CO2 concentrations (Ci) reduced. If ethephon was applied, Ci was higher than that of the control. It is possible that GA3 could improve the photosynthesis rates because GA3 regulated stomata function. Further studies are needed to address how did application of ethephon reduce the photosynthesis rates of Rh. delavayi.