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.

Chronic effects of vapour phase di-n-butyl phthalate (DBP) on six plant species.

A fumigation experiment was performed in which six plant species representing the European flora were exposed to a range of DBP concentrations. Controlled amounts of DBP-saturated air were injected into the ingoing air-streams of plant fumigation chambers, maintaining constant concentrations there for a period of up to 76 days. The target concentrations were a control, 0.8, 1.5, 3.5, and 10.0 microg m(-3). The variation in sensitivity between plant species to atmospheric DBP was quantified on the basis of whole plant biomass in order to derive no-observed-effect-concentrations (NOECs). Significant dose-response relationships, based on realised concentrations, were thus derived using non-linear regression, resulting in NOECs of 0.51 microg m(-3) for Trifolium repens, 0.96 microg m(-3) for Brassica campestris, 1.87 microg m(-3) for Phaseolus vulgaris and 2.21 microg m(-3) for Plantago major. A significant effect was also observed for Holcus lanatus at 12.4 microg m(-3) DBP, but due to the variation at lower levels of DBP exposure, no dose-response relationship could be derived. No significant effect on growth of current year needles in Picea abies was observed, even at the highest level of DBP, 13.7 microg m(-3). Based on statistical extrapolation according to Aldenberg and Slob [Ecotox. Environ. Safety, 25 (1993) 48], an overall predicted no-effect concentration (PNEC) for the plant-atmosphere compartment of 0.33 microg m(-3) DBP was calculated. The PNEC was calculated using the mean and standard deviation of the NOEC for four of the tested species and an extrapolation factor. In addition to changes in leaf colour, leaf crinkling and growth reduction, a number of not quantified observations are described, indicating that DBP affects the physiology as well as the morphology of these species.

Influence of NH3 and SO2 on the growth and competitive ability of Arnica montana L. and Viola canina L.

The effects of atmospheric NH3 and SO2 separately and in combination on the growth and competitive ability of three species of the Violion caninae alliance were investigated. Growth and nutrient concentrations of Viola canina and Arnica montana in mixed culture with Agrostis capillaris were examined in relation to that in monoculture. Seedlings were transplanted into heathland topsoil in pots and placed in open-top chambers for 9 months from autumn to summer, where they were exposed to ambient air, 90 µ m-3 SO2 , 50 µg m-3 NH3 and to the combination of NH2 and SO2 . In the NH3 + SO2 treatment, a more-than-additive increase in nitrogen and sulphur concentrations was observed indicating co-deposition. NH3 influenced the nutritional status of V. canina the most, increasing the nitrogen, phosphorus, and magnesium concentrations and reducing those of potassium and calcium. NH3 fumigation significantly stimulated shoot growth of all three species and root growth of A. capillaris, while SO2 reduced only the root growth of A. capillaris. The relative yield of V. canina was reduced by 20-30% in the presence of the air pollutants. The relative yield of A. montana was stimulated by 30-40% in treatments including SO2 compared with that in ambient air or NH3 alone. The competitive ability of both dicotyledons in mixed culture with A. capillaris was strongly reduced by NH3 and was unaffected by SO2 . The consequences of exposure to NH3 and SO2 for the survival and maintenance of threatened species in heathland vegetation are discussed.

Adaptation of grasses in the Netherlands to air pollution.

In three separate experiments, the response of three populations of Agrostis capillaris L., Nardus stricta L., and Lolium perenne L., from areas differing in ambient air pollution concentrations, were examined in experimental fumigations using SO2 , O3 , NO2 and NH3 . Growth of A. capillaris generally increased following the fumigations, except at the highest pollutant concentrations (120 µg m-3 O3 , alone or combined with 150 µg m-3 SO2 and 35 µg m-3 NO2 ). Growth of each population of N. stricta was stimulated by the SO2 and NH3 combination, but was significantly increased only in the populations originating from the most heavily polluted of the three areas. The growth of L. perenne was not inhibited by any air pollutant or combination of pollutants. Despite a low growth rate in clean air and a large amount of within-population variation, biomass production was significantly stimulated by the highest pollutant mixture. The response of each species to the experimental treatments depended in part on the location from which it originated. This site-dependent (population) response differed between species, suggesting that the selective processes induced by these air pollutant concentrations were insufficient for a clear-cut adaptation to gaseous air pollutants.