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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 1Texas 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 Ám2). Current research is focused on reconciling elevated CO2 effects on respiratory metabolism, cell ultrastructure and rates of leaf respiration in field-grown trees.



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