Abstract, Ecological Society of America Annual Meeting, Snowbird, UT, August, 2000.

TISSUE, D.T.¹, J.D. LEWIS², K.L. GRIFFIN³, O.R. ANDERSON³, S.D. WULLSCHLEGER.^{4 1}Texas Tech University, Lubbock, TX ., ²Fordham University, Armonk, NY , ³Columbia University, Palisades, NY, ⁴Oak Ridge National Laboratory, Oak Ridge, TN.

Leaf respiration in sweetgum: direct and indirect effects of elevated CO₂.

Trees exposed to elevated CO₂ generally show increased rates of photosynthesis and growth, but the effects of CO₂ enrichment on leaf dark respiration are more variable. Direct (short-term) effects of elevated CO₂ on respiration are observed when CO₂ is rapidly increased, resulting in changes in respiratory metabolism, including enzyme activity. Indirect (long-term) effects on respiration are observed after long-term growth at elevated CO₂ and are mediated through elevated CO₂ effects on leaf growth rate, nonstructural carbohydrate concentration, and tissue composition. In this study, sweetgum trees were grown in a FACE facility in ambient (36 Pa) and elevated (55 Pa) CO2; measurements were taken using a LiCor 6400 (cuvette sealed with vacuum grease to reduce potential for leaks) in the second growing season of fumigation. Direct CO2 effects were observed as short-term increases in CO₂ reduced respiration by 14% (P<0.05), although this effect was fully reversible. Indirect CO₂ effects were also observed as dark respiration at growth CO₂ was reduced 14% on a leaf weight basis (P<0.01) and reduced 12% on a leaf area basis (P<0.1) in elevated CO₂. Despite reduced respiration, growth in elevated CO₂ increased the number of mitochondria by 140% (0.4 vs. 1.02 mitochondrion per 100 µm²). Current research is focused on reconciling elevated CO₂ effects on respiratory metabolism, cell ultrastructure and rates of leaf respiration in field-grown trees.