The Response of Temperate Tree Seedlings Grown in Elevated CO"2 to Extreme Temperature Events

Mean global temperatures have been predicted to increase in the next century; if so the frequency of extreme temperature events may also increase. Extreme temperatures may damage plant tissue and consequently limit the survival of certain plant species in a region. Elevated concentrations of CO 2 in the atmosphere alter plant allocation, physiology, and growth, and may accentuate or ameliorate the damage from extreme temperatures. In this paper we explore the interactive effects of atmospheric CO 2 concentration, nutrient levels, and exposure to extreme temperatures on seedlings of three species of temperate deciduous trees. A 1—d exposure to extreme heat (45°C) significantly decreased conductance the following day and decreased biomass as measured at both 35 and 105 d following the extreme temperature event, regardless of atmospheric CO 2 concentration. The most shade—tolerant species, striped maple, was most severely impacted by the extreme heat event in both CO 2 environments. Furthermore, striped maple seedlings grown in elevated CO 2 concentrations had a significantly greater decrease in biomass due to the extreme heat event as compared with striped maple plants grown in ambient CO 2 concentrations at 35 d after the heat event; however, at the end of the growing season at 105 d post treatment, this difference was not significant. A one—night exposure to low temperatures (4°C) did not affect biomass for any of these species. With an increase in global mean temperatures, the frequency of extreme temperature events, particularly hot weather events, may increase and may extend to shaded understory sites. If the frequency of extremely high temperatures increases, the role that temperature extremes may play in changing competitive interactions and thus affecting community composition may increase in importance, as these temperatures appear to severely alter plant survival and growth in some species.