Abstract

The objectives of this study were to quantify changes in leaf freezing resistance and carbohydrate concentrations caused by long-term (6 years) exposure to elevated CO 2 (ambient: 360 μl l −1 , elevated: 600 μl l −1 ) in five dominant plant species growing in situ in a native temperate grassland. Across all five species tested from three functional groups, the mean temperature at which all leaves were damaged ( T100 ) significantly ( P  = 0.016) increased from −9.6 to −8.5 °C under elevated CO 2  , and a similar marginally significant ( P  = 0.079) reduction was observed for the mean temperature that caused 50% leaf damage ( T50 ), from −6.7 to −6.0 °C. The mean temperature at which initial leaf damage was observed ( T0 ) was not significantly influenced by elevated CO 2  . Although concentrations of soluble sugars (+25%, P  = 0.042), starch (+53%, P  < 0.001), and total non-structural carbohydrates (TNC, +40%, P  < 0.001) were significantly higher under elevated CO 2  , leaf freezing resistance actually decreased under elevated CO 2  . Concentrations of soluble sugars were positively correlated with freezing resistance when viewed across all five community dominants, but within any individual species, no such relationships were found. We also found no evidence for our original hypothesis that increased concentrations of soluble sugars increase freezing resistance. Thus, future atmospheric CO 2 levels may instead increase the risk of late spring freezing damage. Furthermore, the strong differences in freezing resistance observed among the species, along with decreased freezing resistance, may increase the risk of losing species that have inherently weak freezing resistances from the plant community. Copyright 2001 Annals of Botany Company

Received: 11 January 2001 ; Accepted: 22 February 2001

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