Document: JAC-3-34-13

Elevated CO₂ concentrations enhance frost damage to eucalypt seedlings under field conditions.

EGERTON, J.J.G.*, C.J.HOLLY, W.E.PIPPEN and M.C.BALL

Australian National University. ¹

Abstract:
Elevated CO₂ concentrations can adversely affect acclimation to freezing temperatures in temperate evergreens, but the mechanism(s) is unknown. One possibility is that reduction in foliar nitrogen concentrations induced by growth under elevated CO₂ concentrations could adversely affect freezing tolerance. We tested this hypothesis by growing seedlings of snow gum (Eucalyptus pauciflora) under field conditions in three nitrogen treatments in open-topped chambers flushed with either ambient air or air enriched with CO₂ to twice normal levels (350 and 700 ppm, respectively). Plants were subject to several light frosts of 0 to -1 ^oC in the first three weeks of growth in autumn. However, minimum temperature on 25 April dropped to -6.4 ^oC at seedling canopy height within the chambers. Three days later, seedlings growing under ambient [CO₂] had lost an average of 0.4% of total leaf area to freeze-induced necrosis. In contrast, seedlings grown under elevated [CO₂] lost an average of 33% of total leaf area. Freeze-induced injury under elevated [CO₂] was partially alleviated by nitrogen nutrition, with the median loss in leaf area for plants grown under high, medium and low nitrogen regimes being 24, 31 and 44%, respectively. All plants grew vigorously in autumn, with the most rapidly growing plants in the highest nitrogen treatment suffering the least freeze damage. Leaves without visible freezing injury also showed a greater loss in F_v/F_m under elevated [CO₂], with values averaging 0.686 and 0.425 under ambient and elevated [CO₂], respectively. These results confirm earlier reports of enhanced susceptibility to freeze damage in plants grown under elevated [CO₂], and have far reaching consequences for prediction of plant performance in a future high [CO₂] world.

Keywords: Eucalyptus, elevated [CO₂], frost, freeze-induced damage, Nitrogen, open-top chambers, chorophyll fluorescence.

This abstract is being presented at: 8:00 AM in session:
Oral Session #40: Elevated CO₂ In Forest Systems.