Growth and Photosynthetic Responses of One C3 and Two C4 Chenopodiaceae Plants to Three CO2 Concentration Conditions

Growth and photosynthetic responses of one C3 and two C4 plants in the family Chenopodiaceaein three CO2 concentration ([CO2]) conditions-low (about 243 μmol mol-1, LC), present (about 378, PC), andhigh (about 465, HC)-were investigated in open top chambers. The relative growth rate (RGR) and netassimilation rate in the C3 plant, Chenopodium album, increased with increasing [CO2], though the RGR wasnot enhanced significantly in the HC condition. The leaf area ratio and leaf weight ratio of the C3 plant drasticallydecreased with increasing [CO2], suggesting that the C3 plant invests more biomass to leaves in lower [CO2]conditions. The two C4 plants, Atriplex glauca and A. lentiformis, showed relatively small changes in those growthparameters. These photosynthetic-pathway-dependent responses suggest that growth patterns of C3 and C4plants have been altered by past increases in atmospheric [CO2] but that there will be relatively little furtheralteration in the future high-CO2 world.