Differences in ozone response between two Finnish wild strawberry populations

Abstract

The sensitivity of two Finnish wild strawberry ( Fragaria vesca) populations of seed origin (Kainuu 64°N, 27°E; Etelä-Häme 61°N, 25°E) to slightly elevated tropospheric O 3 was studied during two summers in open-top chambers (OTC; NF=non-filtered air and NF+O 3=non-filtered air+supplemental O 3) and on open-field plots (AA=ambient air). The hypothesis was that the southern Finnish population may be less O 3 sensitive, as the ambient O 3 levels are higher there and, consequently, some selection may already have occurred. The seedlings were moved to an experimental field and planted into a mixture of humus and sand (3:1) without growing pots on 11 June 1998. In the northern areas, elevated O 3 concentrations are episodic, and we hence fumigated the NF+O 3 plants for 8 h a day on 5 days a week as follows: ambient air+30 ppb in June, ambient air+20 ppb in July and ambient air+10 ppb in August. The accumulated exposure over a threshold of 40 ppb reached 5040 ppb h in the NF+O 3 OTCs in June–August 1998, but only 1156 ppb h by mid-August in 1999, when the fumigations were started on 23 June. During the first summer, the shoot (−16%) and root (−13%) biomasses in the NF+O 3 strawberries of the Kainuu population decreased, whereas those in the NF+O 3 strawberries of the Etelä-Häme population increased (+22 and +20%, respectively). However, there was no difference in the runner biomass between the populations. On the whole, the AA plants had the highest biomass in summer 1998. This pointed to a noteworthy chamber effect. In 1999, the proportion of fruiting plants was markedly higher in the NF+O 3-treated Kainuu population than in the Etelä-Häme population. The average number of red, yellow and brown leaves was also higher in the NF+O 3 plants of the Kainuu population than in those of the Etelä-Häme population or in the NF plants of the Kainuu population. However, the differences were not statistically significant due to large variation in the number of discoloured leaves between the individual plants in the NF+O 3 treatment, particularly in the Kainuu population. The results thus suggest that the Kainuu population was more sensitive to O 3 than the Etelä-Häme population and responded to an O 3 exposure far below the proposed critical level of 7000 ppb h.