The effects of elevated ozone and chronic drought on leaf pigments and abscisic acid contents in early and late-flush leaves of Shantung maple (Acer truncatum Bunge)

The changing color of leaves in autumn is not only necessary for the growth of foliage trees but is also important for urban landscape interests. Red color in maple leaves relates to the synthesis of anthocyanin and the degraded pigments.Ozone( O_3) is an important phytotoxic pollutant,which may affect the basic physiological functions of plants due to its highly reactive oxidative characteristics. The increased consumption of fossil fuels in China has led to increased emission of O_3 precursors and visible plant injury induced by high O_3 concentration frequently occurs around Beijing. In addition,trees are often subjected to periodic drought in North China with the frequency and the severity of drought events projected in the background of climate change. Drought in summer usually coincides with episodes of high O_3 concentrations,which,together,may affect plant growth including color expression and leaf senescence of foliage tree species in fall. Although numerous publications have reported the effects of elevated O_3 concentration or drought stress on trees,little is known about the possible interactions between anthocyanin and flavonoid in Asian maple species. To investigate the effects of chronic drought stress and elevated O_3 concentrations on leaf pigments and abscission of Shantung maple( Acer truncatum Bunge),we set up 12 open-top chambers with four treatments( AW: non-filtered ambient air and well watered; AW + 60: nonfiltered ambient air plus 60 n L / L O_3 and well watered; AD: non-filtered ambient air and drought; AD + 60: non-filtered ambient air plus 60 n L / L O_3 and drought) in a suburb of Beijing,China. Total chlorophyll( total Chl),carotenoid( Car),anthocyanin,flavonoid,and abscisic acid( ABA) contents in early and late-flush leaves were measured in October of the first year. Leaves that unfolded from July 1 to 7 were marked as early-flush leaves and the AOT40( The cumulative O_3 exposure,which was described as the accumulated hourly mean O_3 concentrations over 40 ppb during O_3 fumigation period)was 28.2 [mu]L L~(-1)h when harvested. Late-flush leaves unfolded from September 1 to 7 and the AOT40 was 14.2 [mu]L L~(-1)h when harvested. The results showed:( 1) For early-flush leaves,elevated O_3 significantly decreased the total Chl and Car contents by 21% and 29. 6%,respectively,increased anthocyanin and flavonoid relative contents by 34. 1% and 7. 3%,respectively,and increased ABA contents by 19. 8%. Drought stress decreased the tota