M. Cui et al., CO2 EXCHANGE AND GROWTH OF THE CRASSULACEAN ACID METABOLISM PLANT OPUNTIA-FICUS-INDICA UNDER ELEVATED CO2 IN OPEN-TOP CHAMBERS, Plant physiology, 103(2), 1993, pp. 519-524
CO2 uptake, water vapor conductance, and biomass production of Opuntia
ficus-indica, a Crassulacean acid metabolism species, were studied at
CO2 concentrations of 370, 520, and 720 muL L-1 in open-top chambers
during a 23-week period. Nine weeks after planting, daily net CO2 upta
ke for basal cladodes at 520 and 720 muL L-1 Of CO2 was 76 and 98% hig
her, respectively, than at 370 muL L-1. Eight weeks after daughter cla
dodes emerged, their daily net CO2 uptake was 35 and 49% higher at 520
and 720 muL L-1 of CO2, respectively, than at 370 muL L-1. Daily wate
r-use efficiency was 88% higher under elevated CO2 for basal cladodes
and 57% higher for daughter cladodes. The daily net CO2 uptake capacit
y for basal cladodes increased for 4 weeks after planting and then rem
ained fairly constant, whereas for daughter cladodes, it increased wit
h cladode age, became maximal at 8 to 14 weeks, and then declined. The
percentage enhancement in daily net CO2 uptake caused by elevated CO2
was greatest initially for basal cladodes and at 8 to 14 weeks for da
ughter cladodes. The chlorophyll content per unit fresh weight of chlo
renchyma for daughter cladodes at 8 weeks was 19 and 62% lower in 520
and 720 muL L-1 Of CO2, respectively, compared with 370 muL L-1. Despi
te the reduced chlorophyll content, plant biomass production during 23
weeks in 520 and 720 muL L-1 of CO2 was 21 and 55% higher, respective
ly, than at 370 muL L-1. The root dry weight nearly tripled as the CO2
concentration was doubled, causing the root/shoot ratio to increase w
ith CO2 concentration. During the 23-week period, elevated CO2 signifi
cantly increased CO2 uptake and biomass production of O. ficus-indica.