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Carbon Dioxide and Water Fluxes of C3 Annuals and C3 and C4 Perennials at Subambient CO2 Concentrations

H. W. Polley, H. B. Johnson and H. S. Mayeux
Functional Ecology
Vol. 6, No. 6 (1992), pp. 693-703
DOI: 10.2307/2389966
Stable URL: http://www.jstor.org/stable/2389966
Page Count: 11
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Carbon Dioxide and Water Fluxes of C3 Annuals and C3 and C4 Perennials at Subambient CO2 Concentrations
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Abstract

1. The C3 annuals, Avena sativa and Brassica kaber, and C3 and C4 perennials, Prosopis glandulosa and Schizachyrium scoparium, respectively, were grown in a 38-m long chamber along a continuous gradient of daytime CO2 concentrations ([CO2]) from near the current 350 μ mol mol-1 to 150 (annuals) or 200 μ mol mol-1 (perennials). Diurnal CO2 and water fluxes were calculated for plant stands in five consecutive, 7.6-m lengths of the chamber arranged linearly along the [CO2] gradient. 2. The ratio of night respiration (RN) to daytime net assimilation (PD) was greatest in A. sativa/B. kaber exposed to mean [CO2] below 200 μ mol mol-1, while RN/PD differed little among five stands of P. glandulosal S. scoparium that were grown at mean [CO2] from 219 to 331 μ mol mol-1. 3. Evapotranspiration was reduced and water-use efficiency (WUE) was increased in A. satival B. kaber stands by higher [CO2]. 4. PD and WUE of P. glandulosal S. scoparium were not related to [CO2] across either of two growing seasons. Both PD and WUE, however, were greater at higher [CO2] in three of four stands when [CO2] was varied on consecutive days. 5. We conclude that past increases in atmospheric [CO2] have promoted higher WUE and increased carbon uptake in C3-dominated ecosystems.

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