Growth of 27 herbs and grasses in relation to ozone exposure and plant strategy

Potted specimens of 27 Swedish native herbs and grasses were exposed to three different ozone concentrations, CF (charcoal filtered air), NF (non-filtered air) and NF+ (1.5 x non-filtered air) in open-top chambers from 2 July to 5 August 1994. The species represented a wide range of different plant strategies according to the C-S-R model. The results show that the stress-tolerators, S, had a smaller mean relative growth rate, (R) over bar, during the exposure period and also a smaller accumulation of biomass compared with other strategies. The species with the intermediate strategy, CSR, had a (R) over bar similar to that of the species with a large component of C, the competitor strategy, and/or R, the ruderal strategy, whereas the net accumulation of biomass was smaller in the CSR group. This difference between (R) over bar and net growth for the CSR species compared to the species of other strategies, can be explained by a slower growth for the CSR group during the establishment phase. In the present investigation the response to ozone was very small regardless of plant strategy, although there was a weak trend towards slower growth with higher ozone concentration, 18 out of 27 species having a greater growth in CF than in NF+. The growth of one typical stress-tolerant species, Festuca ovina L., was stimulated significantly by ozone. Visible injury, most likely caused by ozone, was noticed in three species, Dactylis glomerata L., Dactylis aschersoniana Graebn. and Phleum alpinum L. Although there were no major restrictions to plant growth in terms of water, nutrients or space in the present open-top chamber experiment, the variability in all climatic factors was as large as in the ambient air. This might harden the plants and make them less sensitive to ozone compared to plants grown in the laboratory under controlled and optimal conditions with low variability.