Abstract: Effects of elevated CO₂ concentration on growth and CO₂ fixation of Phalaenopsis were studied
under elevated CO₂ [ (700 ±50) μmol·mol^-1 , (1 000 ±50) μmol·mol^-1 ] and ambient CO₂ concentra
tions [ (360 ±30) μmol·mol^-1 , control ] at 30 d ( short-term experiment) and 150 d ( long2term experi
ment) after exposure to the corresponding CO₂ concentrations. The results showed that the net CO₂ absorp tion
rate reached a maximum at 2 ∶00 A.M., with 134.11% in ( 700 ±50 ) μmol·mol^-1 and 435.3% in
(1 000 ±50) μmol·mol^-1 higher than control at 30 d, while the increase rate decreased with time. Elevated
CO₂ resulted in the increase of the accumulation of titratable acids ( TA ) which increased by 65.05% in
(700 ±50) μmol·mol^-1 and 119.42% in (1 000 ±50) μmol·mol^-1 at 30 d compared to control, but de
creased slightly thereafter. Elevated CO₂ treatment also resulted in the accumulation of carbohydrates ( soluble
sugar and starch) in leaves, and the accumulation rate in ( 1 000 ±50 ) μmol·mol^-1 was higher than in
(700 ±50) μmol·mol^-1. Compared with control, the fresh mass in (700 ±50) μmol·mol^-1 and (1 000 ±
50) μmol·mol^-1 increased by 23% and 49% at 60 d, and 50% and 94% at 150 d, respectively; the dry
mass in (700 ±50) μmol·mol^-1 and (1 000 ±50) μmol·mol^-1 was increased by 38% and 57% at 60 d,
and 19% and 64% at 150 d, respectively. These results demonstrated that elevated CO₂ has significant effect on the growth of Phalaenopsis.

Key words: Phalaenopsis, Elevated CO₂, Net CO₂ absorption rate, Growth