AOBPreview originally published online on October 2, 2002
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Annals of Botany 90: 593-598, 2002
© 2002 Annals of Botany Company
Initial Net CO2 Uptake Responses and Root Growth for a CAM Community Placed in a Closed Environment
1 Biosphere 2 Center, Columbia University, Box 689, Oracle, AZ 85623, USA
* For correspondence at: Department of Organismic Biology, Ecology, and Evolution, University of California, Los Angeles, CA 90095-1606, USA. Fax +1 310 825 9433, e-mail psnobel{at}biology.ucla.edu
Received: 22 May 2002; Returned for revision: 25 June 2002; Accepted: 16 July 2002 Published electronically: 2 October 2002
To help understand carbon balance between shoots and developing roots, 41 bare-root crassulacean acid metabolism (CAM) plants native to the Sonoran Desert were studied in a glass-panelled sealable room at day/night air temperatures of 25/15 °C. Net CO2 uptake by the community of Agave schottii, Carnegia gigantea, Cylindropuntia versicolor, Ferocactus wislizenii and Opuntia engelmannii occurred 3 weeks after watering. At 4 weeks, the net CO2 uptake rate measured for south-east-facing younger parts of the shoots averaged 1·94 µmol m–2 s–1 at night, considerably higher than the community-level nocturnal net CO2 uptake averaged over the total shoot surface, primarily reflecting the influences of surface orientation on radiation interception (predicted net CO2 uptake is twice as high for south-east-facing surfaces compared with all compass directions). Estimated growth plus maintenance respiration of the roots averaged 0·10 µmol m–2 s–1 over the 13-week period, when the community had a net carbon gain from the atmosphere of 4 mol C while the structural C incorporated into the roots was 23 mol. Thus, these five CAM species diverted all net C uptake over the 13-week period plus some existing shoot C to newly developing roots. Only after sufficient roots develop to support shoot water and nutrient requirements will the plant community have net above-ground biomass gains.
Key words: Agave schottii, Carnegiea gigantea, CO2 uptake, crassulacean acid metabolism, Cylindropuntia versicolor, Ferocactus wislizenii, Opuntia engelmannii, plant community, respiration, roots.
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