Response of subterranean clover (Trifolium subterraneum) to ozone in relation to plant age and light conditions during exposure

Abstract

Potted subterranean clover (Trifolium subterraneum) plants of different ages were exposed to 70 nl l −" ozone for 6 h, either during the light or during the dark period in a laboratory-based climate chamber. There was limited visible leaf injury on plants which were 14-20 and 28-34 d old and no significant decrease in biomass after daytime ozone exposure. The oldest leaves of 22-26 d old plants exhibited severe visible injury, which was associated with a significant reduction in biomass in 24-26 d old plants. Thus, ozone-induced visible injury of different magnitude developed in all plants, but was associated with biomass reduction only during a limited period of the plant's lifespan. Apart from modifying ozone uptake by plants, climatic conditions are important as growth modifiers. It is suggested that subterranean clover plants of defined developmental stages should be used in bioindication of ozone. Night ozone exposure injured significantly fewer leaves than day exposure. However, some leaves developed visible injury even after night ozone exposure. Night uptake of ozone may be of more importance in northern than in central and southern Europe, because summer nights are short and, for a certain period, never completely dark.

Visible foliar injury and infrared imaging show that daylength affects short-term recovery after ozone stress in Trifolium subterraneum

“…Plants of different ages were used to determine whether a dim night-time light effect on ozone sensitivity occurred consistently regardless of plant age. The clover species Trifolium subterraneum L. was investigated as it is very ozone sensitive, developing characteristic necrotic spots, is used as an ozone bioindicator, and has been used as an experimental plant within the United Nations Economic Commission for Europe International Co-operative Programme (UNECE ICP Crops) ( Pihl Karlsson et al , 1995 a , b , 2003; Sild et al , 1999 ; Bermejo et al , 2003 ; Gimeno et al , 2004 a , b ).…”