OZONE SENSITIVITY OF GRAPEVINE (VITIS-VINIFERA L.) - EVIDENCE FOR A MEMORY EFFECT IN A PERENNIAL CROP PLANT

Grapevine plants (cv. Welschriesling), cultivated in 50 l-containers, were exposed to different levels of ozone in open top-chambers. Ozone levels equivalent to ambient air did not affect grape yield significan tly. Based on treatments with four ozone levels, for a grape yield red uction of 10 % an ozone critical level of 27 ppm-h (AOT40) was calcula ted. Visual ozone effects were characterized by enhanced senescence of the leaves. The loss of green leaf area in ozone-fumigated plants cau sed severe reductions of carbohydrate import into the grapes. The degr ee of reduction was different in two consecutive year: in the first ye ar of ozone exposure, the critical level for a 10% reduction of monosa ccharide yield in the grapes was 21 ppm-h (AOT40), whereas in the seco nd year the critical level decreased to 11.5 ppm-h. Also measurements of chlorophyll fluorescence revealed a higher susceptibility to ozone in the second fumigation year. This increased sensitivity in consecuti ve years with high ozone doses could indicate a memory effect for the ozone dose in the previous year. But further experiments will be neces sary to rule out other possible causes (e.g. interactions of sink stre ngth and the size of the assimilate pool).