title: Ecosystem carbon exchange in two terrestrial ecosystem mesocosms under changing atmospheric CO2concentrations.
abstract: The ecosystem-level carbon uptake and respiration were measured under different CO2concentrations in the tropical rainforest and the coastal desert of Biosphere 2, a large enclosed facility. When the mesocosms were sealed and subjected to step-wise changes in atmospheric CO2between daily means of 450 and 900 μmol mol-1, net ecosystem exchange (NEE) of CO2was derived using the diurnal changes in atmospheric CO2concentrations. The step-wise CO2treatment was effectively replicated as indicated by the high repeatability of NEE measurements under similar CO2concentrations over a 12-week period. In the rainforest mesocosm, daily NEE was increased significantly by the high CO2treatments because of much higher enhancement of canopy CO2assimilation relative to the increase in the nighttime ecosystem respiration under high CO2. Furthermore, the response of daytime NEE to increasing atmospheric CO2in this mesocosm was not linear, with a saturation concentration of 750 μmol mol-1. In the desert mesocosm, a combination of a reduction in ecosystem respiration and a small increase in canopy CO2assimilation in the high CO2treatments also enhanced daily NEE. Although soil respiration was not affected by the short-term change in atmospheric CO2in either mesocosm, plant dark respiration was increased significantly by the high CO2treatments in the rainforest mesocosm while the opposite was found in the desert mesocosm. The high CO2treatments increased the ecosystem light compensation points in both mesocosms. High CO2significantly increased ecosystem radiation use efficiency in the rainforest mesocosm, but had a much smaller effect in the desert mesocosm. The desert mesocosm showed much lower absolute response in NEE to atmospheric CO2than the rainforest mesocosm, probably because of the presence of C4plants. This study illustrates the importance of large-scale experimental research in the study of complex global change issues.
authors.affiliation: Columbia University/Biosphere 2 Center, PO Box 689, Oracle, AZ 85623, USA email: glin@bio2.edu, Fax: +1-520-896-6214, , , , , , US.
authors.forename: Guanghui
authors.initials: G
authors.lastname: Lin
authors.affiliation: Columbia University/Biosphere 2 Center, PO Box 689, Oracle, AZ 85623, USA email: glin@bio2.edu, Fax: +1-520-896-6214, , , , , , US.
authors.forename: John
authors.initials: J
authors.lastname: Adams
authors.affiliation: Columbia University/Biosphere 2 Center, PO Box 689, Oracle, AZ 85623, USA email: glin@bio2.edu, Fax: +1-520-896-6214, , , , , , US.
authors.forename: Blake
authors.initials: B
authors.lastname: Farnsworth
authors.affiliation: Columbia University/Biosphere 2 Center, PO Box 689, Oracle, AZ 85623, USA email: glin@bio2.edu, Fax: +1-520-896-6214, , , , , , US.
authors.forename: Yongdan
authors.initials: Y
authors.lastname: Wei
authors.affiliation: Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA, , , , , , US.
authors.forename: Bruno D V
authors.initials: BD
authors.lastname: Marino
authors.affiliation: Department of Plant Biology, Carnegie Institution of Washington, Stanford, CA 94305, USA, , , , , , US.
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Berry
keywords: Canopy photosynthesis; Coastal desert; Key words Atmospheric CO2; Net ecosystem exchange; Tropical rainforest