The impact of elevated carbon dioxide on the growth and gas exchange of three C4 species differing ce 171 (2006) 123–131in CO2 leak rates, Physiol. Plant 105

Recent work has suggested that the photosynthetic rate of also indicated that the response of leaf photosynthesis to certain C4 species can be stimulated by increasing CO2 con- elevated [CO2] was light dependent for all three C4 species. The stimulation of leaf photosynthesis at elevated [CO2] wascentration, [CO2], even under optimal water and nutrients. To determine the basis for the observed photosynthetic stimula- not associated with previously published values of CO2 leak rates from the bundle sheath, changes in the ratio of activitiestion, we tested the hypothesis that the CO2 leak rate from the bundle sheath would be directly related to any observed of PEP-carboxylase to RuBP carboxylase:oxgenase, or any stimulation in single leaf photosynthesis at double the current improvement in daytime leaf water potential for the species tested in this experiment. In spite of the simulation of leaf[CO2]. Three C4 species that differed in the reported degree of bundle sheath leakiness to CO2, Fla7eria triner7ia, Panicum photosynthesis, a significant increase in growth at elevated [CO2] was only observed for one species, F. triner7ia. Resultsmiliaceum, and Panicum maximum, were grown for 31–48 from this study indicate that leaf photosynthetic rates ofdays after sowing at a [CO2] of 350 ml l1 (ambient) or 700 ml l1 (elevated). Assimilation as a function of increasing certain C4 species can respond directly to increased [CO2] under optimal growth conditions, but that the stimulation of[CO2] at high photosynthetic photon flux density (PPFD, 1600 mmol m2 s1) indicated that leaf photosynthesis was whole plant growth at elevated carbon dioxide cannot be predicted solely on the response of individual leaves.not saturated under current ambient [CO2] for any of the three C4 species. Assimilation as a function of increasing PPF