Growth and Photosynthetic Responses of One C3and Two C4Chenopodiaceae Plants to Three CO2Concentration Conditions

Abstract

Growth and photosynthetic responses of one <TEX>$C_3$</TEX> and two <TEX>$C_4$</TEX> plants in the family Chenopodiaceae in three <TEX>$CO_2$</TEX> concentration <TEX>$([CO_2])$</TEX> conditions-low (about <TEX>$243{\mu}mol\;mol^{-1}$</TEX>, LC), present (about 378, PC), and high (about 465, HC)-were investigated in open top chambers. The relative growth rate (RGR) and net assimilation rate in the <TEX>$C_3$</TEX> plant, Chenopodium album, increased with increasing <TEX>$[CO_2]$</TEX>, though the RGR was not enhanced significantly in the HC condition. The leaf area ratio and leaf weight ratio of the <TEX>$C_3$</TEX> plant drastically decreased with increasing <TEX>$[CO_2]$</TEX>, suggesting that the <TEX>$C_3$</TEX> plant invests more biomass to leaves in lower <TEX>$[CO_2]$</TEX> conditions. The two <TEX>$C_4$</TEX> plants, Atriplex glauca and A. lentiformis, showed relatively small changes in those growth parameters. These photosynthetic-pathway-dependent responses suggest that growth patterns of <TEX>$C_3$</TEX> and <TEX>$C_4$</TEX> plants have been altered by past increases in atmospheric <TEX>$[CO_2]$</TEX> but that there will be relatively little further alteration in the future high-<TEX>$CO_2$</TEX> world.