Long‐term response of photosynthesis to elevated carbon dioxide in a florida scrub‐oak ecosystem
2002
Ainsworth, Elizabeth A. | Davey, Phillip A. | Hymus, Graham J. | Drake, Bert G. | Long, Stephen P.
The response of photosynthesis was analyzed during canopy closure in a Florida scrub‐oak ecosystem exposed to elevated [CO₂] (704 μmol CO₂/mol air; concentration of CO₂). The species were measured on six occasions, covering different seasons, during the third and fourth year of exposure to elevated [CO₂]. The entire regrowth cycle of this community has been under elevated [CO₂], providing a rare opportunity to assess the differential responses of species during the critical phase of canopy closure. Measurements were taken in order to determine both season‐specific and species‐specific differences in the response of photosynthesis to elevated [CO₂]. Photosynthesis was measured with an open‐gas exchange system, and in vivo rates of Rubisco carboxylation (Vc,ₘₐₓ) and electron transport (Jₘₐₓ) were derived to assess changes in the photosynthetic capacity in the codominant, evergreen oak species. Quercus myrtifolia did not show any change in photosynthetic capacity with prolonged exposure to elevated [CO₂] during any season, and as a result the increase in photosynthesis due to the increased supply of CO₂ was sustained at 72%. The codominant, Q. geminata, showed a loss of photosynthetic capacity with growth at elevated [CO₂], such that during most measurement periods light‐saturated photosynthesis in leaves grown and measured at elevated [CO₂] was no higher than in leaves grown and measured at ambient CO₂. A third oak, Q. chapmanii, showed a response similar to that of Q. myrtifolia. This suggests that at the critical phase of canopy closure in a woody community, elevation of [CO₂] causes a species‐dependent and time‐dependent change in the capacity of the codominants to acquire carbon and energy.
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