PARENT SESSION
Oral Session #58: Elevated CO₂. Presiding: A. Finzi.
Thursday, August 9, 2001. 8:00 AM to 12:00 PM. Madison Ballroom C.

The impact of elevated atmospheric CO₂ on the responses of a Florida scrub-oak ecosystem to the 1998 drought.

Drake, Bert¹, Dijkstra, Paul¹, Hungate, Bruce², Hymus, Graham¹, Li, Jiahong¹, Day, Frank³, Johnson, Dale⁴, Hinkle, C Ross⁵, ^{1 2 3 4 5}

ABSTRACT- We report results of a long-term study of plant and ecosystem responses of a Florida scrub-oak ecosystem to elevated atmospheric C_a during 1998 when precipitation was less than 10% of the previous ten-year average. We measured leaf photosynthesis, ecosystem gas exchange, shoot and fine root growth, and soil water content for the dominant oak species in this ecosystem prior to, during and after the drought was relieved by summer rain in plants exposed to normal ambient and elevated (ambient + 350 ppm) atmospheric C_a in large open top chambers (10 m²). Compared with plants exposed to normal ambient C_a, leaf photosynthesis was stimulated approximately 124% by elevated atmospheric C_a during drought in May but only 85 % in August after the drought had ended. Stimulation of annual shoot growth by elevated C_a doubled from 64% in 1997 prior to the drought to 121% during the drought in 1998. During the drought in spring of 1998, elevated C_a stimulated maximum rates of net ecosystem gas exchange 200 % compared to a stimulation of 100 % in August when the drought was relieved. Similar results were recorded for fine root growth. These results suggest that relative responses of trees to rising atmospheric C_a during water stress will be greater than responses to elevated C_a in unstressed plants.

KEY WORDS: Elevated CO₂, Drought, Ecosystem processes, Open-top chambers