Does interspecific competition alter effects of early season ozone exposure on plants from wet grasslands? Results of a three-year experiment in open-top chambers.

Chronic effects of ozone on wet grassland species early in the growing season might be altered by interspecific competition. Individual plants of Holcus lanatus, Lychnis flos-cuculi, Molinia caerulea and Plantago lanceolata were grown in monocultures and in mixed cultures with Agrostis capillaris. Mesocosms were exposed to charcoal-filtered air plus 25 nl l(-1) ozone (CF+25), non-filtered air (NF), non-filtered air plus 25 nl l(-1) ozone (NF+25) and non-filtered air plus 50 nl l(-1) ozone (NF+50) early in the growing seasons of 2000 through 2002. Ozone-enhanced senescence and visible foliar injury were recorded on some of the target plants in the first year only. Ozone effects on biomass production were minimal and plant response to ozone did not differ between monocultures and mixed cultures. After three years, above-ground biomass of the plants in mixed culture compared to monocultures was three times greater for H. lanatus and two to four times smaller for the other species.

Monitoring the effects of atmospheric ethylene near polyethylene manufacturing plants with two sensitive plant species.

Data of a multi-year (1977-1983) biomonitoring programme with marigold and petunia around polyethylene manufacturing plants was analysed to assess plant responses to atmospheric ethylene and to determine the area at risk for the phytotoxic effects of this pollutant. In both species, flower formation and growth were severely reduced close to the emission sources and plant performance improved with increasing distance. Plants exposed near the border of the research area had more flowers than the unexposed control while their growth was normal. Measurements of ethylene concentrations at a border site revealed that the growing season mean was 61.5 g m(-3) in 1982 and 15.6 g m(-3) in 1983. In terms of number of flowers, petunia was more sensitive than marigold and adverse effects were observed within ca. 400 m distance from the sources for marigold and within ca. 460 m for petunia. The area at risk (ca. 870 m) for ethylene-induced growth reduction was also limited to the industrial zone. Plants were more sensitive to ethylene in terms of growth reduction than in terms of inhibition of flowering. In the Netherlands, maximum permissible levels of ethylene are currently based on information from laboratory and greenhouse studies. Our results indicate that these levels are rather conservative in protecting field-grown plants against ethylene-induced injury near polyethylene manufacturing plants.

Assessing effects of ambient ozone on injury and yield of bean with ethylenediurea (EDU): three years of plant monitoring at four sites in The Netherlands.

EDU (ethylenediurea) and non-EDU-treated bean plants (Phaseolus vulgaris L. cv. Lit) were exposed to ambient air at four rural sites in The Netherlands during the growing seasons of 1994 through 1996 to investigate the responses to ambient ozone. Ozone-induced foliar injury was observed each year and differences in injury between sites depended on year. On average, injury amounted to 27% in 1994, to 8% in 1995 and to 1% in 1996. Injury increased with increasing ozone exposure (AOT40) and the estimated AOT40 value corresponding with 5% injury was circa 3650 nl l(-1) h ozone. The highest ozone levels accumulated at each site for five consecutive days before injury exceeded the proposed short-term critical level for injury development. EDU reduced injury and its protective effect was positively related to the injury intensity in non-EDU-treated plants. Yield of green marketable pods (intermediate harvest) and mature pods (final harvest) was generally reduced in non-EDU-treated plants compared to EDU-treated plants and differences in yield reduction between harvests varied between years. The yield of mature pods was reduced in 1994 and 1996 while the yield of green pods was reduced in 1995 by ozone only. Since yield reduction was not correlated with AOT40. the EDU method was not valid to determine an ozone exposure-yield reponse relationship for bean.

Effects of ambient ozone on injury and yield of Phaseolus vulgaris at four rural sites in the Netherlands as assessed by using ethylenediurea (EDU).

To assess adverse effects of ambient ozone on injury and yield, EDU (ethylenediurea) and non-EDU-treated plants of bean (Phaseolus vulgaris L. cv. Lit) were exposed to ambient air at four rural sites in the Netherlands in 1994. After 6 wk of exposure, the proportion of leaves injured in non-EDU-treated plants was higher than that in plants treated with the antioxidant. A maximal degree of 35 % injury was observed. The highest ozone levels accumulated at each site for three consecutive days before injury clearly exceeded the proposed short-term critical level for injury development. Both injury in untreated plants and the protective effect of EDU differed between sites and were not related to the measured ozone levels. EDU increased the d. wt of dry (mature) pods after 11 wk of exposure but not of green (marketable) pods after 6 wk. The effect of EDU in enhancing dry pod yield did not differ between sites and was 20% on average. The proportional yield increases in EDU-treated plants compared with those of non-EDU-treated plants at the sites were not correlated with the measured ozone levels known to adversely affect bean yield. The available evidence, however, suggests that ambient ozone was involved in the observed yield increase by EDU. When the dry pods were harvested, EDU-treated plants had more leaves than non-EDU-treated ones. The effect of EDU in delaying senescence appears to be an important factor to consider when attempting to evaluate the effect of ambient ozone on pod weight in beans using the EDU approach.