Photosynthetica 2003, 41(3):365-372 | DOI: 10.1023/B:PHOT.0000015460.48593.00

Developmental Change in CO₂ Compensation Concentrations in Spartina alterniflora Results from Sigmoidal Photosynthetic CO₂ Responses

M.O. Bärlocher¹, D.A. Campbell¹, S. Al-Asaaed¹, R.J. Ireland¹

¹ Department of Biology, Mount Allison University, Sackville, Canada

We investigated seasonal patterns of photosynthetic responses to CO₂ concentrations in Spartina alterniflora Loisel, an aerenchymous halophyte grass, from a salt marsh of the Bay of Fundy (NB, Canada), and from plants grown from rhizome in controlled-environment chambers. From late May to August, CO₂ compensation concentrations (Γ) of field-grown leaves varied between 2.5-10.7 cm³(CO₂) m^-3, with a mean of 5.4 cm³(CO₂) m^-3. From September onwards field leaves showed CO₂ compensation concentrations from 6.6-21.1 cm³(CO₂) m^-3, with a mean of 13.1 cm³ m^-3 well into the C₃-C₄ intermediate range. The seasonal variability in Γ did not result from changing respiration, but rather from a sigmoidal response of net photosynthetic rate (P_N) to applied CO₂ concentration, found in all tested leaves but which became more pronounced late in the season. One explanation for the sigmoidal response of P_N to external CO₂ concentration could be internal delivery of CO₂ from roots and rhizomes to bundle sheath cells via the aerenchyma, but the sigmoidal responses in S. alterniflora persisted out to the tips of leaves, while the aerenchyma extend only to mid-leaf. The sigmoidicity persisted when CO₂ response curves were measured from low to high CO₂, or from high to low CO₂, and even when prolonged acclimation times were used at each CO₂ concentration.

Keywords: aerenchyma; bundle sheath; Carex; leaf age; leaf anatomy; net photosynthetic rate; seasonal changes; species differences; Zea

Published: September 1, 2003Show citation