Inhibition of flowering and reproductive success in spreading dogbane (Apocynum androsaemifolium) by exposure to ambient ozone

Ground-level ozone continues to be a cause for concern in terrestrial ecosystems in the northeastern United States and Canada. Spreading dogbane (Apocynum androsaemifolium L.) is one of many indigenous herbaceous plant species exhibiting foliar injury that are commonly monitored in ecosystem assessment programs. Details about possible effects of ambient ozone on reproductive components of these species are lacking. For 103 days, from 31 May to 10 September, A. androsaemifolium plants were grown in open-top chambers in either carbon-filtered air (CF), non-filtered air (NF) (approximately 1 x ambient), or chamberless ambient air plots (AA). Aspects of sexual reproduction were measured to determine whether impairment occurs in polluted air. Additionally, the ozone protectant chemical ethylenediurea (EDU) was applied to foliage to determine its effect on foliar injury. By the end of the experiment visible foliar injury was absent in CF air and nominal in the NF and AA treatments. Plants grown in CF-chamber air produced significantly more flowers and fruits than those grown in either NF-chamber air or AA plots. Flowers produced by plants grown in CF air also survived to mature fruits at a rate 1.7 x greater than plants in NF air and 1.5 x greater than plants in AA plots. We were unable to conclude whether EDU protected plants from foliar ozone injury due to the general lack of foliar injury in ozone-exposed plants. The results demonstrate that foliar injury is not necessarily required to elicit negative effects on sexual reproduction in A. androsaemifolium. Implications for the population biology of A, androsaemifolium related to adverse effects of chronic ozone exposure on sexual reproduction are discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.