ACCLIMATION OF LOLIUM-TEMULENTUM TO ENHANCED CARBON-DIOXIDE CONCENTRATION

Acclimation of single plants of Lolium temulentum to changing [CO2] wa s studied on plants grown in controlled environments at 20 degrees C w ith an 8 h photoperiod. In the first experiment plants were grown at 1 35 mu mol m(-2) s(-1) photosynthetic photon flux density (PPFD) at m s 415 mu l l(-1) or 550 mu l l(-1) [CO2] with some plants transferred f rom the lower to the higher [CO2] at emergence of leaf 4. In the secon d experiment plants were grown at 135 and 500 mu mol m(-2) s(-1) PPFD at 345 and 575 mu l l(-1) [CO2]. High [CO2] during growth had little e ffect on stomatal density, total soluble proteins, chlorophyll a conte nt, amount of Rubisco or cytochrome f. However, increasing [CO2] durin g measurement increased photosynthetic rates, particularly in high lig ht. 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 d iscussed in relation to the limitation of growth by sink capacity and the modifications in the plant which allow the storage of extra assimi lates at high [CO2].