Response of C3, C4, and intermediate Flaveria species to elevated CO2 and temperature

Numerous studies have shown positive responses of C₄ species to elevated CO₂, primarily due to increased water use efficiency under dry growth conditions.  However, the effects of elevated CO₂ and temperature on C₄ dicots species has only been examined in a few studies.  Extensive research on the CO₂ response of C₃ species has shown that dicots generally show larger increases in biomass accumulation in response to elevated CO₂ than monocots.  We compared the effects of elevated CO₂ and increased temperature on biomass accumulation, photosynthesis responses, and chlorophyll fluorescence in four dicot species in the genus Flaveria that utilize different photosynthetic cycles.  We found stronger responses to elevated CO₂ than expected under well-watered conditions in the C₄ species F. trinervia.  The treatments did not affect leaf nitrogen content or photosynthesis rates of F. trinervia but leaf area, above ground biomass, and WUE increased under elevated CO₂, suggesting lower rates of water loss for a given photosynthetic rate.  The other C₄ species, F. kochiana, grew very slowly and showed very little response to the environmental treatments.  Elevated CO₂ increased the above ground biomass of the intermediate species, F. ramosissima but increased temperature greatly reduced plant biomass.  In the C₃ F. pringlei, biomass accumulation increased in response to elevated CO₂ but growth was not reduced under high temperatures as predicted.  This result indicates that F. pringlei has a high capacity to acclimate and perform well under different growth conditions, a result supported by field observations that F. pringlei grows in a wide variety of habitat types.  There were species level correlations between leaf nitrogen content, photosynthetic rate, and biomass accumulation but these relationships were not consistent between different environmental treatments.