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Carbon Dioxide Exchange of C₃ and C₄ Tree Species in the Understory of a Hawaiian Forest

Robert W. Pearcy and Howard W. Calkin
Oecologia
Vol. 58, No. 1 (1983), pp. 26-32
Published by: Springer in cooperation with International Association for Ecology
Stable URL: http://www.jstor.org/stable/4216989
Page Count: 7
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Carbon Dioxide Exchange of C₃ and C₄ Tree Species in the Understory of a Hawaiian Forest
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Abstract

Field measurements of photosynthetic CO₂ exchange were made on saplings of a C₄ tree species, Euphorbia forbesii, and a C₃ tree species, Claoxylon sandwicense, in a shaded mesic forest on Oahu, Hawaii. Both species had light responses typical of those generally found in shade plants. Light saturated photosynthetic rates were 7.15 and 4.09 μmol m-2 s-1 and light compensation points were 6.3 and 1.7 μmol m-2 s-1 in E. forbesii and C. sandwicense, respectively. E. forbesii maintained a higher mesophyll conductance and a higher water use efficiency than C. sandwicense as is typically found in comparisons of C₄ and C₃ plants. Under natural light regimes, both species maintained positive CO₂ uptake rates over essentially the entire day because of low respiration rates and light compensation points. However, photosynthesis during sunflecks accounted for a large fraction of the daily carbon gain. The results show that the carbon-gaining capacity of E. forbesii is comparable to that of a C₃ species in a moderately cool, shaded forest environment. There appears to be no particular advantage or disadvantage associated with the C₄ photosynthetic pathway of E. forbesii in this environment.

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