Acclimation of single plants of Lolium temulentum to changing [CO2] was studied on plants grown in controlled environments at 20°C with an 8 h photoperiod. In the first experiment plants were grown at 135 μ;mol m−2 s−1 photosynthetic photon flux density (PPFD) at 415μl l−1 or 550μl l−1 [CO2] with some plants transferred from the lower to the higher [CO2] at emergence of leaf 4. In the second experiment plants were grown at 135 and 500 μmol m−2 s−1 PPFD at 345 and 575 μl l−1 [CO2].
High [CO2] during growth had little effect on stomatal density, total soluble proteins, chlorophyll a content, amount of Rubisco or cytochrome f. However, increasing [CO2] during measurement increased photosynthetic rates, particularly in high light. Plants grown in the higher [CO2] had greater leaf extension, leaf and plant growth rates in low but not in high light. The results are discussed in relation to the limitation of growth by sink capacity and the modifications in the plant which allow the storage of extra assimilates at high [CO2]