PARENT SESSION
Contributed Oral Session 28: Plant Physiology: Effects of Ozone CO₂, and Cavitation
Monday, August 8, 1:30 PM - 5:00 PM, Meeting Room 519 B, Level 5, Palais des congrès de Montréal

Disturbance and elevated [CO₂] promote establishment of woody plants in grasslands.

EGERTON, JOHN^*,1, LOVEYS, BETH¹, BRUHN, DAN¹, PIPPEN, WAYNE¹, BALL, MARILYN¹, ¹ Cooperative Research Centre for Greenhouse Accounting, Canberra, ACT, Australia

ABSTRACT- A field experiment was established to investigate the role of disturbance (here defined as bare soil) and elevated [CO₂] on establishment of tree seedlings in grasslands. Snow gum (Eucalyptus pauciflora) seedlings were grown in open top chambers flushed with either ambient or elevated [CO₂]. Seedlings were planted into bare soil or pasture grass and growth was monitored for nearly 12 months. After the first major freezing event in autumn, seedlings growing in grass lost 59% of their canopy area while those growing in bare soil suffered negligible damage. Tree seedlings growing in bare soil initiated buds and commenced growth earlier in spring than their counterparts growing in grass, consistent with greater soil moisture and higher soil temperatures in the bare soil patches. At the conclusion of the experiment tree seedlings in bare soil under ambient CO₂ were nearly 50 times larger than those surrounded by grass. Tree seedlings growing in bare soil and in grass both benefited from elevated CO₂. However, the combined affects of bare soil and elevated CO₂ resulted in tree seedlings being 80 times larger at the completion of the experiment than seedlings surrounded by grass under ambient CO₂. These results provide evidence that combined effects of disturbance and increase in atmospheric [CO₂] could have promoted the recent invasion of grasslands by woody plants in many parts of the world.

Key words: elevated CO₂, disturbance, vegetation thickening, grass-tree interactions